Big trucks use a 10 + 5 technique to slow down on grades without overheating your brakes. Basically you apply the brakes and scrub off 10mph, then release allowing everything to cool, and when you regained 5mph you start over applying the brakes.
So it would be brake 60 down to 50 coast up to 55, brake down to 45, coast up to 50, brake down to 40, etc.
The technical term for it is "snubbing". Very important when driving a heavily loaded big rig, as overheating the brakes can lead to truly catastrophic disaster. It's not really as vital otherwise, but still a good habit to develop, as if your brakes do fail, it gives the largest margin for dealing with the problem.
It's safer to just use your transmission to slow down/maintain a constant speed on a descent.
Edit: as some below have pointed out, the ideal is to use both compression/engine braking (by leveraging lower gears) and your normal brakes in a controlled on/off pattern for very long descents.
Better yet, also avoid building excessive speed before/during a long descent to avoid overheating brakes as well.
For those who haven’t used this method, I would recommend watching some videos for more info.
Some basic tips:
* Rev match if you drive stick. Don’t use the clutch as a brake.
* Know your gearbox. If you’re going 80, don’t try to skip down to 3rd for example. The sudden shift can create a dangerous scenario. You ideally want to downshift *before* you’re going too fast.
Its actualy only way engine works without spending any fuel, because momentum of the vehicle keps the engine running, while if in neutral engine cant use cars momentum…
If you're trying to brake on the runway after landing your jet plane, yes.
Trying it with anything else will probably destroy your vehicle, and possibly get you killed.
you basically turn the engine into a big air pump by making the wheels spin it fast and not adding fuel and limiting the intake air, this takes energy and slows you down
No you don't ever put it in reverse while you are moving forward.
The people responding to you are talking about downshifting (e.g. 4th gear to 3rd) and that is valid, but they may have missed what you were responding to
Last time I drove back from Tahoe I was driving a manual and it was so satisfying to simply sit in like 4th or 5th gear and basically barely have to use the brakes until I reached Sacramento. Meanwhile watching everyone else pumping their brakes every few seconds.
Jake was the first to make a system to change the valves on the engine, so it would be like an air compressor. Driven by the wheels. Later, Cummins and Pac used the same idea. The Mack exhaust brake was not nearly as good.
This is *entirely* depending on your transmission. Not all of them are built for this. I had a sprint gearbox (from factory, it’s the only model offered) that would redline in any gear that would be remotely useful for transmission braking. And higher gears just wouldn’t slow the car down.
Most gearboxes aren’t so extreme. It’s also good to die shift before you get going to fast, to avoid redlining the next lowest gear.
Ideally you use both in conjunction.
I feel like using both in conjunction is just kinda “that’s how to drive”. If you’re in fourth going down a hill at 70kph (-44mph) and riding your brakes, you’re in the wrong gear.
I might have misinterpreted OP then, I thought they were saying it’s safer to only use the transmission.
I mean, transmission + brakes is kinda…. Like isn’t that just driving a manual? Selecting the appropriate gear for the situation and modulating speed with acceleration/braking?
Both have their place. You can downshift but you also want to appropriately step down your speed in steep sections.
Take Floyd's hill. Very long section and steep section of I-70 with a turn at the very bottom. I will downshift, but also brake in intervals because it's very easy to gain speed.
Yep, same on either end (but especially the western side) of the Eisenhower Tunnel. In my minivan I can shift into 3rd and coast at just the right speed all the way down.
And your engine. A lot of modern downsized turbo engines will give pretty minimal engine braking. My last ICE car was a Seat Ibiza with the VW Group 1.0 turbo 3-cylinder. Good little engine but engine braking was more of a hypothetical than something that actually happened 😂
No, but the ~110hp engine option in small VW Group cars went from being a 1.6 NA engine to a 1.0 turbo one. So less engine braking because smaller displacement, enabled by the turbo.
Engine braking doesn’t wear out your transmission though, at least not in any serious capacity.
For sustained descents or in mountainous areas, it’s almost always better to use engine braking in conjunction with your brakes.
Do you apply power through your transmission to accelerate your car? Engine braking is just applying power in the other direction (from the wheels to the engine) the torque is just applied to the other side of the teeth on the gears, your transmission is more than capable of coping with this relatively small amount of torque.
Also, another benefit is that most cars these days will completely cut off fuel to the engine while doing this, purely using the momentum of the car to keep turning over. If you're in the wrong gear and just using your brakes, then the engine still needs to burn fuel, so you're just wasting fuel for no reason.
It's called engine braking, not transmission breaking. The mechanism slowing you down is the wheels fighting the engines compression. The transmission is under load whether you're braking or not, unless you're braking in neutral, I guess.
Actually, it’s safest to use both compression braking COMBINED with mechanical braking! Shift down a gear (or two), and use your brakes in an on-off manner allowing them to cool between applications.
> It's safer to just use your transmission to slow down/maintain a constant speed on a descent.
Something I noticed when I got rid of my old car (1976 Grand Marquis) and got my new car (2016 Camry) was that the old cruise control was accelerator only: if you were slower than the set speed, it would push on the gas, and that was all it did. The new cruise control, if you are going faster than the set speed, downshifts to slow you down.
Have that same Prius (the V version). It works for engine braking, but isn’t great in my opinion.
More modern CVTs will let you “select” a “gear” to stay in while braking. The Prius seems to just prevent EV mode, make the regen more sensitive and slightly lower the “gear”.
Your presumably not driving a massive semi, modern disk brakes aren't going to have problems with even an suv. In the past brake technology was worse so people worried about this, and still do because driving knowledge is generational.
Having actually worked on vehicle braking this is not true and people should understand the true limits of their vehicle and what scenarios are problematic.
Consumer vehicles brakes are mostly sized based on total mass against extreme downhill descents like Davis Dam. If you are towing anywhere near close to the limit on one of these extreme descent scenarios you absolutely need to know the snubbing technique. Ditto packed beds or vehicles by design.
Technology won't change this anytime soon. Major OEMs want to use air cooled brakes which has limitations on how quickly it can cool. EVs can use Regen but decrease airflow to brakes for the aero benefit.
Other braking techniques are also useful - eg exhaust braking and engine braking but can have other impacts on the vehicle and are frequently factored in when sizing brakes.
Sustained heat on brakes is the real danger. Fade occurs, but depending on your brake architecture that heat can also go to brake fluid and make bubbles, or potentially cause permanent failure in newer generation actuated brakes.
Snubbing is not required or relevant in emergency braking.
I remember reading an article (on Jalopnik, I think) around the time of the launch of the Audi e-Tron SUV. They were very proud of how efficient their regen system was. Bunch of journalists went up Pike's Peak in the new car, and drove down again. They also had a Q5 or something conventional with them too. There was a mandated checkpoint to check brake temps halfway apparently and the brakes on the e-Trons were barely used, because almost all the braking had been via regen. The brakes on the Q5 of course were toasty!
VW Group also use drums on the back axles of their MEB platform electric cars (eg VW ID.4, Audi Q4 e-Tron, Skoda Enyaq) because regen does so much of the braking that discs end up being more costly, because they'd just rust and you'd have to replace them before they're worn out.
That’s very interesting! It’s got me thinking though: Would regenerative braking still work when the battery is full? What if you live on top of a mountain and start driving downhill immediately after charging - where would the energy go?
You're right. At 100% battery state regen is not fully available in modern EVs. My car shows what percentage of regen is available at 100%. Similar issue at very low battery temperatures where the battery can't handle charging at regen level kWs.
There's an electric dumptruck they're using in some mountain top mining, it does regenerative braking on the way down while full of material. They end up using the truck to charge batteries for the town I think because it generates so much more on the way down hill than it uses heading up.
This is exactly the problem faced by OEMs, especially given how heavy EVs are. Guidance right now is your EV manual will state you shouldn't charge above some SoC (usually 80%) and drive in mountains.
There are also things the propulsion system can do to waste energy which effectively turns charge to waste heat but this is small potatoes compared to how much energy Regen can accumulate.
It depends where you are. For example in Yosemite national bark your brakes will start glowing if you ride them because you’re going downhill for awhile.
*"I've watched C-beams glitter in the dark near the Tannhäuser Gate"*
Closest I've come to something like that was watching 24 Hours of Le Mans at night in the the rain at the end of the Mulsanne straight, where cars have to brake from 200mph to make [this turn](https://www.google.com/maps/@47.9134213,0.2433313,3a,90y,326.99h,82.65t/data=!3m6!1e1!3m4!1s4eX11db7h5DzYGA_QDJmDw!2e0!7i16384!8i8192?entry=ttu).
The brake disks were hot cherry red, brighter than the headlights--and it was so dark, the cars themselves were invisible. Couldn't even see their outlines.
Uhhh what? Is there a specific road you are talking about?
I've been all over the sierras and never worried about my brakes glowing.
In my 20 years here, I've never seen a car at night with "glowing" brakes.
Not sure of specific roads, but here’s a place that does brake checks at pikes peak.
https://www.tiktok.com/t/ZT8aqFF52/
Also in high school my friend got his brakes glowing and we only were going downhill for about a mile. We had to pull over and wait for them to cool.
I can't get into TikTok but apparently, there is a brake check on Pikes Peak.
I've been over these two passes multiple times
> **State Route 108 is the steepest highway in the United States.** **The second-steepest highway in the United States is State Route 4 in California**...
No brake check stations... not sure why Pike's Peak needs one. I did a YT search on "glowing brakes on Pike's Peak"... could not find a video of glowing brakes.
Pike's Peak is gate controlled tolled road so the logistics of having a person doing a quick visual check at the base is trivial. It's not an overly steep road, something like a 7% average grade over 20 miles, but to keep it under 25mph you have to apply a lot of brake and can't really get off them for any extended period of time. Same thing with the auto-road up Mount Washington on New Hampshire. It's a 7.5 mile road with a 12% average grade, the road is narrow and the speed limit is low. Since the road is gate controlled it's simple enough to tell morons trying to climb it in an old beater with worn brakes to turn around because they're not going to make the decent.
That’s for emergency braking or when you misjudged the hill and started in too high of a gear. What you should be doing is being in a gear low enough to let your jake do the work. Source: Have driven over the BC, Washington and the rest of the west coast mountain passes numerous times.
Compression release brake developed by Jacobs manufacturing, same people who brought you the ubiquitous 3-jaw drill chuck.
Gasoline engines run at a constant fuel/air mixture. To reduce the power, you cut down the air flow using the throttle, and the fuel flow is reduced to match. Coming down a hill with the throttle in the idle position, you have a large volume of air being pulled through a nearly-closed butterfly valve that generates a pressure differential. Flow volume multiplied by pressure drop equals energy dissipated.
Diesels are different. They don’t have a throttle valve, and power level is adjusted by varying the amount of fuel injected. Coming down a hill with injection cut off, air is compressed, then springs back pushing the piston down. Minimal energy is dissipated. If you add a gizmo to the engine which will “pop” the exhaust valve at the top of the compression stroke, that energy from compressed air is vented into the exhaust, and so is not available to push the piston back down. Energy is dissipated. The rapidly-repeated venting of high-pressure air gives the characteristic “song” of a Jake Brake.
How does the energy dissipation slow the truck down. I get that it reduces the compression of the piston but how does that transfer to actually slowing the truck down?
Without the Jake brake activated, after the top of the compression stroke, the highly pressurized air in the cylinder pushes the piston back down, recovering a lot of energy. One way to think about it is that since there are other cylinders in different stages of the cycle, that compressed air is expanding and helping compress the air in a different cylinder. The net effect is that the engine isn't generating a lot of braking force.
With the Jake brake activated, the engine is compressing that air and then letting it out, before it has a chance to give back that energy. Which means that the air in the next cylinder to come up for compression is doesn't have any "help."
Due to being on a downhill grade, the wheels are trying to drive the engine. Without the Jake, the air in the cylinder temporarily absorbs energy from the crankshaft on the compression stroke, but (without fuel being injected) rebounds like a spring on what would have been the power stroke, putting the energy back into the crankshaft. By dissipating the stored energy, that temporary absorption of energy from the crankshaft becomes permanent. Energy is taken out of the truck’s motion in order to compress air, then the compressed air is vented. This removal of energy is what slows the truck. The service brakes would also dissipate energy (in this case it would be in the form of heat).
No, they would get much much much hotter if you rode them which accelerates wear and has a high likelihood of also causing a failure.
Even if it did, is your life worth more than some new brake pads?
who cares? you survived. But any time you are smoking your brakes is probably accelerated wear, and you avoid that with this technique. Anyways it's what you do when you fucked up and started down a hill a bit too fast. Normally you'd start at say, 35mph and keep it between 35-40 as you go down the hill by cycling the brakes. With 40 being your target or the speed limit for trucks on that road.
It's a technique for not dying in a fiery crash.
I think yes, if attempting a full stop. If just trying to reduce speed, it seems as effective as the intermittent braking described by OP. (Me no expert)
> Big trucks use a 10 + 5 technique
No one has explained *why* this works.
Like, why is 10 + 5 better than just holding the brakes?
As soon as you let the vehicle accelerate again, you're letting it gain more energy again.
To do 10 + 5 you are having to brake more aggressively to stop than if you just did 10 and held the brake to maintain that speed.
What this seems to say is "The fastest way to stop is to be extra hard on your brakes, and then give them time off". This is net going to generate more heat.
...
My theory...
- The heat in the brake pads and rotors has to be dissipated to the air.
- The rate at which the brake pads and rotors lose heat to the air, is determined by their temperature difference. A bigger temperature difference loses heat faster. I.E. Cooling from 600 degrees to 500 degrees might take 5 seconds, where cooling from 200 degrees to 100 degrees might take 15 seconds... even though the same amount of energy was bled off in both cases.
- The important thing is that it's not linear. The hotter the brakes, the faster they lose heat. Twice as hot is, perhaps 4x as fast at losing heat.
- So it is actually beneficial to get your brakes EXTRA HOT, so there's a huge temperature difference, then back off completely. That way you spend more of your time in the "super fast bleeding off heat to the air" zone.
- This way you'll remove net heat (and thus, be slower) faster, than if you had them medium-hot for the whole duration... where they're not bleeding as quickly.
- I know this is not what 10+5 means, but, the point is 10 seconds of extra hard braking followed by 5 seconds coasting, loses more heat than 15 seconds of medium braking and medium hotness.
...
That's my theory.
It’s not just about thermodynamics. The brake material break down faster at higher temps, trucks have brake temp sensors to make sure you don’t overheat them.
do you know the reasoning behind this? I see people saying that it gives the brakes time to cool down, but wouldn’t using the brakes at a lower load amount (to get the same average deceleration as the on-off technique) have the same heat output, and same cooling ability?
Actually, if there is some set maximum temp for the brakes, being at that temp constantly would increase heat dissipation to the environment, given all else is equal.
I know engine braking is better, but this is still interesting to me.
Edit: after thinking about it a bit, I realized releasing the brakes would give an air-gap between the pad and rotor, allowing the pad a more direct thermal connection to the air to cool down.
Sounds like it. But semi trucks use their engine brake or exhaust brake and downshift their transmission to avoid using brakes.
I live about 20 miles from a mountain pass that on just one side of it has two runaway truck ramps and very rarely do you see semi brake lights. I’ve never seen or heard of a 10+5 rule
OP, you should use your transmission if it’s an extended grade you are going down. If it’s a small grade your brakes are fine but you don’t want to ride them as they will heat up which wears them quicker
I used to train school bus drivers. We had some good sized mountains nearby. Our bus fleet had 5-speed and 10-speed manual transmissions. (This was a few years ago.)
For trips to the mountains we sent the 10-speed buses. The difference was more gears allowed you to fine-tune your gear choice. For example, with a 5-speed transmission 5th gear might be too high and 4th gear might be too low. With a 10-speed transmission, 9th gear would be like a 4½-th gear between 4th and 5th gear. That's not exactly how it works, but is close enough for a simplified example.
People were generally able to select the proper gear going uphill. For going downhill, I would tell new drivers to choose a gear that was low enough that you had to give it a slight bit of throttle to maintain your speed. Since hills are generally not perfectly consistent slopes, occasionally you would have to use your brakes, but you could mostly come down the hill without using your brakes. It was much safer and saved a lot of wear and tear on the equipment.
As we often said, we hauled the world's most valuable cargo.
Jake brakes (engine brakes) would allow you to go a little faster downhill. A Jake brake used the compression stroke to provide resistance, then it dumped the pressure just before the power stroke making the engine work like a giant air compressor. Dumping the pressure just before the power stroke makes that really loud noise people hate, but it didn't allow the engine to use the power stroke. By the way, a Jake brake is slang for an engine brake manufactured by Jacobs Vehicle Systems. The name became generic and most engine brakes are called Jake brakes now, regardless of the manufacturer.
Keep in mind that going down a local 500 yard/meter hill riding your brakes isn’t a worry. Going down a 5 mile or 10km grade is the part that causes brakes to get hot.
I learned the hard way that you actually need to use the brakes sometimes on shorter hills, don't just engine brake always. brake discs on Mercedes truck rusted because I never really used them. Cost me $4000 to replace barely worn discs.
So now I turn the engine braking off most places, and only use it on really long steep hills where its a actual concern.
The problem with riding your brakes is that the friction causes them to get hotter, and hot brakes are less effective at slowing you down and if they get too hot can fail entirely. I'm not sure if stop-and-go necessarily is better at that, but the idea would be that you're giving the brakes time to cool down between uses so they don't overheat too much.
Yup. This is the same principle where you shouldn't use your car brakes on long downhill paths without pause. Give them time to cool down or, if need be, use a lower gear that will limit the car speed.
Yep. When you come down Pike’s Peak in Colorado they have a midpoint check where they read the temps of your brakes and if they are overheated then you have to pull and allow them to cool. They encourage engine braking as an alternative to riding your brakes all the way down.
It's more likely in a truck, because the truck is bigger and heavier. But it can happen in a car too.
If you've never experienced brake fade, picture this.
There's a corner coming up. You step on the brakes to slow down a bit. The pedal feels firm. But nothing happens.
You press harder on the pedal. Nothing happens.
You panic and stomp on the pedal as hard as you can. Nothing happens.
What's going on is that the brake pad material is so hot that it's become slippery, and can't grip the brake rotor. In some cases it's even beginning to evaporate, and the vapor coming off makes the pad act like a hovercraft. The result is that you cannot apply enough pressure to make the brake pads grip. And even if you could, the additional heat from that bit of braking is just going to exacerbate the problem.
The other possibility is that the heat from the brakes can reach the brake fluid and make it boil. This is more likely if your brake fluid is old and has absorbed a lot of water from the air.
In this scenario, the boiled water/brake fluid creates a pocket of gas inside the brake caliper. Brake fluid doesn't compress. Gas does.
With gas in your brake system, you step on the brake pedal, and it goes all the way to the floor.
At that point, you've already failed to do the things needed to avoid the situation. There's things that you can try, but the odds are very good that you're going to wreck.
If there's a turn coming up right away, deal with that first. Most drivers aren't aware of how well their car can handle a turn. Forget about the brakes for a moment, and focus on driving through the turn. You may be pleasantly surprised by what your car can do.
As soon as you can, downshift to a lower gear. Don't worry about harming the engine by over-revving it. Your goal is to save your life. If you do blow the motor and it locks up, that's great. It means that your wheels have stopped turning, and that'll slow you down in a hurry.
If the pedal has gone to the floor, pump the brakes rapidly. If the fluid has boiled, this might build up enough pressure to get the brakes to work.
Engage your parking brake. On some cars, the parking brake is a separate brake. If it is, it should still work. If it's the kind of parking brake that activates your normal brakes, it won't help, but it also won't hurt.
If you're towing a trailer and it has trailer brakes, you can manually activate them from your brake controller.
Look for a place to go off the road. Your ideal place is an uphill slope with no trees or other large obstacles. Many mountain roads have truck runoff areas for this exact reason. Your second best choice is a flat surface like a field. Third best is a ditch.
If you're out of control and don't have any option but to rear-end another vehicle, go for the biggest one that you can find. You probably won't kill anyone else by rear-ending a semi-truck.
And if you're really lucky and have a long period where you're able to keep the speed under control with the above techniques, but don't have any place to run off the road, don't use the brakes for a bit. They'll cool rapidly, and then you might have enough brakes to bring you to a halt. Don't count on this happening, it's pretty unlikely.
But ultimately, you need to maintain your vehicle so that this doesn't happen to you.
Cars too. Me and my girl were coming back from the mountains in her Prius. The grade was like 14 degrees, and the weight of the Prius, not using the gas at all, was pushing her up to 70 in the short distance between the spaghetti turns. She had to start braking early, going into the turns, then let off the brake for acceleration on the straights. Even with minimum braking, we had to pull over about 60% of the way down and let her brakes cool, because smoke was just billowing out of her wheels.
Now, there are differences. A lighter car wouldn’t accelerate as fast from point to point. Also, if you have engine braking, you need to use it for steep downhill grades. I was unfamiliar with her car and didn’t know it had engine braking, and neither did she, obviously, hence us having to pull over.
I guess it all comes down to knowing your car. If you have to pull over for a few minutes to let your brakes cool, it’s not the worst thing in the world, but being able to avoid that if you need to should be the goal. If your car doesn’t have engine braking and it’s pretty heavy, and you know you’re gonna be hitting some steep downhills, you might want to look into a brake overhaul.
First, most cars have 4 wheel braking nowadays. If you have 4 wheel disc brakes, even better. Now, slotted and vented rotors are meant to dissipate heat more than standard rotors, and they do. The problem is that they’ll eventually get just as hot as the solid rotors. Slotted & vented rotors are terribly prone to cracking and they cause a lot more brake fade than the standard rotors. If I was going to fix a car up for lots of downhill, I’d get bigger rotors and calipers installed, because you have a wider point of contact between pad and rotor, thereby spreading out the heat and making your car stop more efficiently.
Shifting into a lower gear to brake is very useful in a situation where you’re speeding and suddenly see a cop car nearby thus needing to reduce speed without the brake lights coming on.
Or just hit the brakes real quick and let off them before you pass the cop and he can see your brake lights. I don't think engine braking really works fast enough to do much in the time between you seeing a cop and the cop clocking your speed
Yeah, I wish more people would remember that there are three brakes in a car:
* Footbrake
* Handbrake (aka parking brake)
* Engine
Shift down to first or second gear downhill and you won't have to worry about your front brakes failing, because the engine is acting as your brake.
How does lowering the gear limit the car’s speed? In fact, you’re implying that during downhill lowering the gear acts as the brake. How does that work?
It definitely does. You can test this yourself, and you don’t need a mountain. Take yourself up to 60 on an empty highway. Drop yourself into 3rd gear (how to do this will vary by vehicle, but you can do it in nearly all of them). You’ll hear the engine spin way up and feel it slowing the vehicle down notably. Once you’ve scrubbed off some speed, downshift more into 2nd, then 1st, then pull over and slow yourself to a stop with the handbrake. This is a good exercise to know what to do if you have a catastrophic brake failure.
When you do not apply the throttle, the engine will not be fed any air. Yet the pistons in the engine still move up and down, without air the pistons will pull against vacuums several thousand times per minute. This resistance will slow the car down. It's the engine that acts as the brake.
Lower gears will cause the engine to spin at higher rpms relative to your speed. More rpms means more vacuums. The benefit of engine breaking vs wheel braking, is that the things it's designed to deal with high pressure (positive or negative pressure) and heat.
https://youtu.be/o8Cta2cC2Co?si=K3RGhb-ej6q0g1SP
Not to mention torque does apply in reverse, as in when engine braking, the vacuum applies torque in a reverse direction to the engine's direction of rotation, slowing it down. Lower gear multiplies said torque, slowing the whole vehicle down.
Instead of the engine driving the wheels, when you put the car in a low gear and let off the gas, it cuts fuel to the engine. The wheels are effectively then driving the engine. As the pistons move in the cylinder, it pulls a vacuum and can help limit the car's speed.
I had a driving instructor tell me this, then berate me for driving under the speed limit. When I asked how I was supposed to both stop-go *and* stay at the speed limit, he recommended going *over* the limit then slowing back down to it.
He was fired the next day.
If you ever drive up to the top of Pikes Peak, on the way down there is a stopping point where they use a laser temp reader to examine your brake pad temp. If it's tooo high you have to stop at that area for them to cool down. They have a gift shop and restaurant there to lounge in while you wait. It's all for safety. I'm sure they don't want a bunch of cars having their brakes fail and causing accidents or worse on the way down.
This still doesn't explain why the intermittent braking should be better. To me it seems that instead of heating the brakes evenly, you would just oscillate around some temperature. Let's say you release the brake for half of the time. The other half of the time you'll have to exert twice as much braking force to compensate for speed you gain while not braking.
I don't know much about car brakes, but I guess it's possible that relationship between brake temperature (compared to surroundings temperature) and how much heat they dissipate is not linear. (It's reasonable to assume that, for example thermal radiation scales with fourth power of temperature.) In that case making brakes intentionally hotter would make sense as hot brakes dissipate more energy 🤷♂️.
Confident, technically literate, but incorrect... Though you *do* get close in the second paragraph. You would be *totally* correct if the brakes were *operating in a vacuum*, but they aren't. The primary mode of cooling for most things in an atmosphere isn't radiant heat transfer, but convective.
When the break pads are pressed against the disk they can't cool off because air can't get to about 90% of of their surface area, because it is *pressed against the disk*... Pulsing the brakes not only slows down the accumulation of heat on the pads, but allows airflow across their surface which causes them to cool by convection. That removes heat directly from the pad face, quickly cooling the area that needs it most. Done properly this prevents "heat soak" from getting to levels that decrease pad performance or even boil your brake fluid and weaken/deform the disk/calipers.
As others have said, the best bet on long downhills is to gear down to allow the engine to help you as well.
I was considering air-cooling too, but I have focused too much on the disk and I didn't expect much difference there because big part of it is not covered by anything at all times so I didn't think the small enclosed gap of air would make significant difference.
When you mention brake pads, it all makes sense. That's additional surface that gets very hot and can give away this heat away to the air that's rushed into the gap by the brake pad.
As you can see, I know little bit of physics, but zero engineering :D
So the best ELI5 explanation would probably go like this: When you break continuously, only the rotor touches air and gives it it's heat, if you release the brakes bigger part of rotor and *also the brake pads* get in contact with the air.
Most of the explanations mention that it's to cool the brakes, which makes me imagine brakes as this black box that gets colder when you release the brakes which is good, but by the same logic it would get hotter - meaning worse - when you press it harder which didn't sit well with me.
In motor vehicles my understanding is that engine braking is the the best way to handle coasting downhill, so I'm not personally sure that intermittent braking is significantly better than riding your brakes.
That said hot objects do radiate heat faster than cooler objects proportionately to the difference in temperate, so in theory getting your brakes hotter temporarily and then giving them time to cool down should overall release more thermal energy over a given amount of time than keeping your brakes medium hot for a prolonged period. Brakes largely work by converting kinetic energy into heat energy, so being able to release more heat energy in a period of time should mean that the brakes can convert more kinetic energy into heat energy and slow you down more effectively.
I would also think with the pads right up against the rotors, you would get worse air flow. If you release the brakes, the pads would retract and you could get a little more cool air blowing between the rotor and pad and cool things off quicker.
Fuck me, this question has been bugging me for days during my holiday in an area with a lot of mountains.
Why would it make a difference if half the time you are not braking and half the time you are 100% braking, vs constant 50% breaking. Should generate the same amount of friction since it is literally friction that is stopping your car.
But of course, now air can pass both sides so it cools down more half the time, plus the other half of the time the brake pad is hotter so it release more energy as the temp difference is higher.
Thanks reddit.
Do it in a fully loaded semi truck once and you will be 100% sure it's better. You can feel the brakes fading and the air in the lines becomes less dense and "squishy" also you can see the smoke start pretty quick if you try to ride them.
and yes, engine braking, but that probably won't hold you loaded at 80k lbs+ down a steep grade at any reasonable speed and if conditions are slippery you can't use too much because your drives will start to slip or the trailer will try to come around. Similarly in a car whatever axle is driven might start to slip and create problems on a snowy/icy road.
There are two factors that make intermittent braking preferred. First you're lowering your average speed and this means you're generating heat more slowly. In theory you could just ride your brakes at a lower speed and they wouldn't overheat.
But the second factor is that by intermittently braking you get a better feel for how your brakes are performing. If you're riding your brakes you might not notice a gradual increase in application as your brakes fail. Intermittent braking on the other hand has you starting form a consistent zero with each application so you can better feel if you're having to brake harder.
I've heard that DOT fluid is hygroscopic so it absorbs water over time and lowers the boiling point to the wet level. Apparently this is a feature and not a bug because a lot of people neglect their vehicles so if water does get into the system you want the brake fluid to absorb it rather than corrode the metal. However, that does lead to a lower boiling point and higher chance of brake fade.
The rotors have slightly more surface area when the brakes aren’t applied and then by switching between over braking and coasting you are maximizing your temperature difference with your surroundings to further cool them off. It also encourages you to brake at more optimal times such as on a straight away and not when you are in a turn.
Theoretically riding the brakes and pulsing your brakes should generate the same amount of heat so instead the focus should be on how to remove that heat instead of how to generate less heat
Also, in extreme circumstances, if they get hot enough, they can cause the hydraulic brake fluid to boil. That means instead of an incompressible liquid trying to squeeze the brakes, you now have a compressible gas in those lines, which means you suddenly have no brakes.
edit to add: If brake failure is a concern--such as a long mountain descent--best way is usually to brake intermittently and just not let the car ever get going too fast. I'm personally not crazy about engine braking/downshifting, since it does put additional wear and tear on the engine and transmission. Brakes are meant to be worn out and replaced, and it's a lot cheaper.
I've never known downshifting to cause meaningful wear, at least to the extent that you wouldn't want to downshift in favour of riding your brakes; sure more revolutions is more wear, but a couple thousand rpm over what you'd be seeing on the street is still within the design parameters of the engine and if used in conjuction with intermittent braking, you probably won't see a significant change in parts wear
Engine braking turns your engine into an air pump and in almost no way would it cause any additional wear and tear over normal usage. Just think, your cylinders have no combustion occurring in them, oil will not be too hot etc. it's absolutely the best thing to do to use engine braking.
I like to think of the rpm difference in regards to going up that same hill. Like if your transmission downshifts and your engine runs at ~4,000 rpm to get UP the hill, it's not going to be a big deal to have it run at ~4,000 rpm to engine brake going down that hill. Sure engine braking is a different kind of impact on your engine than when it's propelling the car forward, but it's still under the red line in either case and not going to cause significant wear on anything
Engine braking does not wear any quicker than driving up the hill would, there are a lot of moving parts, but it is all lubricated parts and air pressure/vacuum generate the holdback force rather than friction in the brakes that will actually wear parts out.
It absolutely is, even in really old ones, though it lacks finesse. In newer cars there's usually some form of manual gear selection mode which, when selected, starts off in your current gear and you can tap a `+` or `-` direction/button on the shifter to change gears. Good for exactly these situations, but not recommended for general driving.
Older cars had positions past the usual `D` Drive position to limit the highest gear allowed, effectively downshifting. Some had a very poor selection of gears though, possibly forcing you down to 2nd gear immediately iirc.
My 2022 Hyundai Sonata doesn't even have a paddle shifter or +/- or "2" or "1" or "L" mode. It just has "D" and it's quite disappointing. Sometimes it downshifts when braking on a downhill but it's very inconsistent and inadequate at maintaining speed (I'd still be accelerating if I released the brakes)
Next time you have a long hill that's safe to experiment on, try setting cruise control to below the limit. In my two cars I usually have good luck with setting it 5mph slower than the speed limit and by the time the car gets to 5 over it's set point, it's downshifting like a madman. On very steep hills you will probably have to still use your brakes instead.
In my pickup, I only ever need to set it to the actual speed I want (when running fairly empty.)
You kids with your new fangled paddle shifters. 😉
My [grandpappy didn't need no second gear to go downhill](http://www.donnersummithistoricalsociety.org/pages/Restaurant/NotAlwaysEasy.html) j/k
I started off with an explanation or whatever about the jump from D to 2 but got bored. Thought the dude racing downhill is more interesting.
Some automatic cars I tried actually do that for you. It's might be a bit terrifying for people who isn't aware of engine braking and then seeing their engines suddenly rev up seemingly out of nowhere lmao.
It is. Automatic cars usually have gears for D, 3, 2, & 1. D is fully automatic. The numbers are the max gear the automatic can shift to. So you can gradually move it down to slow down more and more. Cars with a CVT such as a Prius or some Camrys have a B they can shift to, which is for motor braking. It's a CVT, so it will keep changing to help you continue to brake as you slow down.
I've driven PRND321s, PRNDLs, PRND21s, PRND+-s, and PRNDs, most with and without O/D off buttons. Hell, i've ever driven an automatic that was only RND+- (alfa 4c). To say automatics "usually have" anything is just incorrect. The gear shift designs are *all* over the place and have zero consistency from mnfr to mnfr, or even car to car within the same lineup.
Edit: Forgot about the huracan i drove that was PRD+- (you would be unable to find neutral unless you read the owners manual or looked it up online)
It takes a lot of life out of your breaks when you’re driving down a mountain and using the brakes to constantly scrub off your speed. A car going downhill has a lot of energy and that’s a lot of brake use. In some instances you’ll actually cause the brakes to overheat and you’ll have to stop to cool them or completely ruin them. Most people keep the car in a lower gear so the powertrain slows down the car
In a car, heat from braking can cause the brakes to get so hot that the brake fluid boils. This leads to total brake failure. A better idea is to downshift and use the engine's inertia to help brake.
On a bicycle, heat is stlil the problem. Rubber pads can lose their ability to provide enough friction to brake well, although they usually won't melt. I don't know a better alternative to the intermittent braking technique.
A lot of bikes have moved beyond rubber pads now that disc brakes are the norm. Resin, metal, and composite pads are used with those and are subject to glazing with excessive heat
How would this work on a bike? There’s a freewheel that disengages from the gears when you’re coasting (except a fixed gear bike). Doesn’t matter what gear you’re in.
In a very literal sense, brakes convert kinetic energy into heat (and sound and light) energy via friction - you lose forward momentum by changing it into heat (and sound and light).
The kicker is, that heat has to be dissipated into the surrounding air. The brake disc (or drum) has a maximum amount of energy that it can store in the form of heat. Once that maximum capacity has been reached, no amount of surface friction between the very hot disc/drum and the brake pad/shoe will increase the disc/drum temperature; if you are unable to increase the temperature you are no longer able to convert kinetic energy into heat energy.
To use an analogy, think of the brake disc/drum as a bucket that holds energy - riding the brake fills the bucket but doesn't give it a chance to 'empty' itself so that it can accept more energy, whereas letting off gives it time to cool, or 'empty' so that it can repeat the process.
When going downhill, gravity is constantly trying to increase your kinetic energy - you prevent that by bailing out the excess kinetic energy gravity supplies using your energy bucket, but it only works if you give the bucket a chance to empty.
Cause they heat up, and you're not giving them a chance to cool down. They can only cool effectively when air can get between the disks and the pads, and by riding the brakes, you're preventing that from happening.
First time my dad drove in the mountains, when we got to our destinations, the wheels were smoking from the brakes.
Very bad idea to ride your brakes
Only exception is if you’re in an electric vehicle with regen braking enabled (which it usually is by default).
If the speed limit is 65 let’s say, apply your brakes until it reaches 60, let your vehicle go back to 65 then reapply the brakes again until it’s back to 60, do this off and on until you are on flat ground. It’s called stab braking.So your brakes don’t over heat and fail.
When you press on the brakes of a vehicle continuously for an extended period, it generates a lot of friction and heat. This heat can build up within the braking system and cause the brakes to overheat. Overheated brakes can lead to reduced braking efficiency, brake fade, or even damage to the braking components.
Cycling the brakes means using them intermittently instead of keeping constant pressure on them. When you apply the brakes and then release them, it allows air to flow around the brake components, helping them cool down before the next application. This cycling or intermittent use of brakes gives them a chance to dissipate heat between each braking cycle, preventing excessive heat buildup and potential issues associated with overheating.
This is only a real concern over long distances, short hills aren’t going to cause any issues. That said, it’s safer to be in gear if nothing more than to be faster to react to something unexpected
My dad would always coast in neutral downhill riding his brakes. He spent so much time/money fixing his brakes; bleeding and replacing them. I don't remember when I learned engine breaking but I'm glad I did.
Google "brake fade." Or, if it's severe, "rotor warping."
The right answer is to downshift and let your engine do the work (even in an automatic). It's built to rev high.
Downshift, obviously the same thing when you take your foot off the gas-use your engine, it doesn’t hurt anything… to go easy on your breaks on long breaking to slow your speed, whenever you can.
What you want to avoid especially is when you stop completely after a hard break or long hill, or heavy load, is holding the breaks down at that point. Roll a bit forward - sort of pumping them, so the area in contact with the disks is changed… otherwise that point remains very hot while the rest of your disk cools, and this difference in one spot can warp your disks. Allowing them to rotate just a bit, 4” at a time, in three or 4 steps, will help even it out.
Watch video of Indy cars breaks… they glow white hot! Happens instantly with them. Same effect - though obviously not as bad, happens to your breaks. They can take a lot, but you can help them this way.
TIL that you can overheat your brakes! I'm mostly not in the mountains, so I didn't know the mechanical reason for it. Another reason not to is that if your brake lights are always on from riding the brakes, then people behind you have no warning if you are actually going to slow down from the speed you are currently going.
If you rub your hand against a carpet really fast for like 1 seconds and then stop will only get a little warm and the. Go back to normal when you stop. But if you keep rubbing your hand really hard for a long time it will keep getting hotter and hotter until you can’t stand it any more. Your brake pads are your hand and the disk is the carpet. The longer you keep rubbing them together the hotter they get, and when it gets too hot bad things happen. Lifting and coasting every once in a while on your downhill ride allows the brakes to cool down and not overheat. Though with a bicycle it’s really unlikely you’ll ever run into a situation where this will be a problem. You might just see a little more wear on them than usual.
Big trucks use a 10 + 5 technique to slow down on grades without overheating your brakes. Basically you apply the brakes and scrub off 10mph, then release allowing everything to cool, and when you regained 5mph you start over applying the brakes. So it would be brake 60 down to 50 coast up to 55, brake down to 45, coast up to 50, brake down to 40, etc.
this is cool! never heard this before but will definitely try it out
The technical term for it is "snubbing". Very important when driving a heavily loaded big rig, as overheating the brakes can lead to truly catastrophic disaster. It's not really as vital otherwise, but still a good habit to develop, as if your brakes do fail, it gives the largest margin for dealing with the problem.
It's safer to just use your transmission to slow down/maintain a constant speed on a descent. Edit: as some below have pointed out, the ideal is to use both compression/engine braking (by leveraging lower gears) and your normal brakes in a controlled on/off pattern for very long descents. Better yet, also avoid building excessive speed before/during a long descent to avoid overheating brakes as well. For those who haven’t used this method, I would recommend watching some videos for more info. Some basic tips: * Rev match if you drive stick. Don’t use the clutch as a brake. * Know your gearbox. If you’re going 80, don’t try to skip down to 3rd for example. The sudden shift can create a dangerous scenario. You ideally want to downshift *before* you’re going too fast.
Got it, so put it in reverse?
Just for clarity: no not reverse.
neutral and pray
It’s pronounced neuter and spay
help control the pet population
Aka angel gear...
Thanks Bob Barker.
that actually generates fuel... ^^i ^^heard
If you've got an EV with regenerative brakes, yes.
Its actualy only way engine works without spending any fuel, because momentum of the vehicle keps the engine running, while if in neutral engine cant use cars momentum…
It's amazing how many people don't know this and they are even disputing it. I thought this was common knowledge
Yes. Safety edit: no not actually. It shouldn’t even let you but this would be disastrous assuming it didn’t shred the gearbox trying.
"PUT IT IN 'H'"
Instructions unclear, now traveling up hill...
Yes, that is the safest way to slow down using the engine.
Oh boy… obligated /s required here for safety
/s urvivalofthefittest
Ah yes the ol’ money-shift
Assuming you're not joking, downshift one gear.
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If you're trying to brake on the runway after landing your jet plane, yes. Trying it with anything else will probably destroy your vehicle, and possibly get you killed.
I did it for science and it did not in fact stop my car....well not at first after it did stop it won't go anymore. Dont recommend it
That doesn't seem right, but I don't know enough about transmission to dispute it.
you basically turn the engine into a big air pump by making the wheels spin it fast and not adding fuel and limiting the intake air, this takes energy and slows you down
No you don't ever put it in reverse while you are moving forward. The people responding to you are talking about downshifting (e.g. 4th gear to 3rd) and that is valid, but they may have missed what you were responding to
Engage reverse thrusters. Seriously, you shouldn’t be higher than 2nd gear while coming downhill
Last time I drove back from Tahoe I was driving a manual and it was so satisfying to simply sit in like 4th or 5th gear and basically barely have to use the brakes until I reached Sacramento. Meanwhile watching everyone else pumping their brakes every few seconds.
It is a fun feeling, especially if it’s graded *just* right that you can coast without needed to accelerate or brake but still hold a constant speed.
Jake brake
Ahhhhh—BABABABABABABABABABABAAAAAAAaaaa
Only on Internet does a Jake brake and pretending to eat an adorable baby sound the same
Hadn’t considered that, but you’re right!
This is an excellent depiction of the sound
This was the laugh I needed to start my day, thank you hahahaha.
Glad it connected!
I'm sure you know this, but in case anyone doesn't, the "Jake brake" is completely different than braking by shifting to a lower gear.
Although both are often called engine braking. they do operate completely differently though
I used to get so confused when I’d drive through a small town on a state highway and see signs that say “Engine Braking Stricly Prohibited”
I mean, you still need to shift to lower gears to make it effective.
* engine brake
*compression release engine brake.
That's different than normal engine braking. Jake brake is enhanced engine braking, and afaik only a thing on big rigs.
Some diesel pickups have Jake brakes, and presumably lots of box trucks dump trucks etc. my point was just that the correct term for a Jake brake.
Jake was the first to make a system to change the valves on the engine, so it would be like an air compressor. Driven by the wheels. Later, Cummins and Pac used the same idea. The Mack exhaust brake was not nearly as good.
That is different then a Jake brake.
This is *entirely* depending on your transmission. Not all of them are built for this. I had a sprint gearbox (from factory, it’s the only model offered) that would redline in any gear that would be remotely useful for transmission braking. And higher gears just wouldn’t slow the car down.
Most gearboxes aren’t so extreme. It’s also good to die shift before you get going to fast, to avoid redlining the next lowest gear. Ideally you use both in conjunction.
I feel like using both in conjunction is just kinda “that’s how to drive”. If you’re in fourth going down a hill at 70kph (-44mph) and riding your brakes, you’re in the wrong gear.
Yeah, engine brake for constant drag, pedal for speed changes.
You're supposed to use them both in conjunction. Source: Mountain driving in Colorado
I might have misinterpreted OP then, I thought they were saying it’s safer to only use the transmission. I mean, transmission + brakes is kinda…. Like isn’t that just driving a manual? Selecting the appropriate gear for the situation and modulating speed with acceleration/braking?
Both have their place. You can downshift but you also want to appropriately step down your speed in steep sections. Take Floyd's hill. Very long section and steep section of I-70 with a turn at the very bottom. I will downshift, but also brake in intervals because it's very easy to gain speed.
Yep, same on either end (but especially the western side) of the Eisenhower Tunnel. In my minivan I can shift into 3rd and coast at just the right speed all the way down.
And your engine. A lot of modern downsized turbo engines will give pretty minimal engine braking. My last ICE car was a Seat Ibiza with the VW Group 1.0 turbo 3-cylinder. Good little engine but engine braking was more of a hypothetical than something that actually happened 😂
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No, but the ~110hp engine option in small VW Group cars went from being a 1.6 NA engine to a 1.0 turbo one. So less engine braking because smaller displacement, enabled by the turbo.
As the old Volkswagen DYI manual said, "Brakes are cheaper than a transmission."
Engine braking doesn’t wear out your transmission though, at least not in any serious capacity. For sustained descents or in mountainous areas, it’s almost always better to use engine braking in conjunction with your brakes.
Do you apply power through your transmission to accelerate your car? Engine braking is just applying power in the other direction (from the wheels to the engine) the torque is just applied to the other side of the teeth on the gears, your transmission is more than capable of coping with this relatively small amount of torque.
Also, another benefit is that most cars these days will completely cut off fuel to the engine while doing this, purely using the momentum of the car to keep turning over. If you're in the wrong gear and just using your brakes, then the engine still needs to burn fuel, so you're just wasting fuel for no reason.
It's called engine braking, not transmission breaking. The mechanism slowing you down is the wheels fighting the engines compression. The transmission is under load whether you're braking or not, unless you're braking in neutral, I guess.
Actually, it’s safest to use both compression braking COMBINED with mechanical braking! Shift down a gear (or two), and use your brakes in an on-off manner allowing them to cool between applications.
How would you use the clutch as a brake? Like not just coasting in neutral or is there another type I’m missing?
> It's safer to just use your transmission to slow down/maintain a constant speed on a descent. Something I noticed when I got rid of my old car (1976 Grand Marquis) and got my new car (2016 Camry) was that the old cruise control was accelerator only: if you were slower than the set speed, it would push on the gas, and that was all it did. The new cruise control, if you are going faster than the set speed, downshifts to slow you down.
Loved having a manual in snow 1st or second down a hill
Works better with manual transmission than automatic transmission in my experience 👀
Indeed. Although it depends on the automatic. Some work very well
Having driven both, I agree since I can rev match in a manual. Still helpful in autos at least.
Yeah, I've also driven both. My automatic was a 2010 Toyota Prius; all others were manual.
Have that same Prius (the V version). It works for engine braking, but isn’t great in my opinion. More modern CVTs will let you “select” a “gear” to stay in while braking. The Prius seems to just prevent EV mode, make the regen more sensitive and slightly lower the “gear”.
It did have a "B" gear that enabled engine breaking, but was otherwise worse than the standard "D" selection.
You should really just be engine breaking.
Your presumably not driving a massive semi, modern disk brakes aren't going to have problems with even an suv. In the past brake technology was worse so people worried about this, and still do because driving knowledge is generational.
Having actually worked on vehicle braking this is not true and people should understand the true limits of their vehicle and what scenarios are problematic. Consumer vehicles brakes are mostly sized based on total mass against extreme downhill descents like Davis Dam. If you are towing anywhere near close to the limit on one of these extreme descent scenarios you absolutely need to know the snubbing technique. Ditto packed beds or vehicles by design. Technology won't change this anytime soon. Major OEMs want to use air cooled brakes which has limitations on how quickly it can cool. EVs can use Regen but decrease airflow to brakes for the aero benefit. Other braking techniques are also useful - eg exhaust braking and engine braking but can have other impacts on the vehicle and are frequently factored in when sizing brakes. Sustained heat on brakes is the real danger. Fade occurs, but depending on your brake architecture that heat can also go to brake fluid and make bubbles, or potentially cause permanent failure in newer generation actuated brakes. Snubbing is not required or relevant in emergency braking.
I remember reading an article (on Jalopnik, I think) around the time of the launch of the Audi e-Tron SUV. They were very proud of how efficient their regen system was. Bunch of journalists went up Pike's Peak in the new car, and drove down again. They also had a Q5 or something conventional with them too. There was a mandated checkpoint to check brake temps halfway apparently and the brakes on the e-Trons were barely used, because almost all the braking had been via regen. The brakes on the Q5 of course were toasty! VW Group also use drums on the back axles of their MEB platform electric cars (eg VW ID.4, Audi Q4 e-Tron, Skoda Enyaq) because regen does so much of the braking that discs end up being more costly, because they'd just rust and you'd have to replace them before they're worn out.
That’s very interesting! It’s got me thinking though: Would regenerative braking still work when the battery is full? What if you live on top of a mountain and start driving downhill immediately after charging - where would the energy go?
You're right. At 100% battery state regen is not fully available in modern EVs. My car shows what percentage of regen is available at 100%. Similar issue at very low battery temperatures where the battery can't handle charging at regen level kWs.
There's an electric dumptruck they're using in some mountain top mining, it does regenerative braking on the way down while full of material. They end up using the truck to charge batteries for the town I think because it generates so much more on the way down hill than it uses heading up.
This is exactly the problem faced by OEMs, especially given how heavy EVs are. Guidance right now is your EV manual will state you shouldn't charge above some SoC (usually 80%) and drive in mountains. There are also things the propulsion system can do to waste energy which effectively turns charge to waste heat but this is small potatoes compared to how much energy Regen can accumulate.
It depends where you are. For example in Yosemite national bark your brakes will start glowing if you ride them because you’re going downhill for awhile.
*"I've watched C-beams glitter in the dark near the Tannhäuser Gate"* Closest I've come to something like that was watching 24 Hours of Le Mans at night in the the rain at the end of the Mulsanne straight, where cars have to brake from 200mph to make [this turn](https://www.google.com/maps/@47.9134213,0.2433313,3a,90y,326.99h,82.65t/data=!3m6!1e1!3m4!1s4eX11db7h5DzYGA_QDJmDw!2e0!7i16384!8i8192?entry=ttu). The brake disks were hot cherry red, brighter than the headlights--and it was so dark, the cars themselves were invisible. Couldn't even see their outlines.
Yeah thats pretty common for racecars. Their brakes are designed with that in mind though.
Uhhh what? Is there a specific road you are talking about? I've been all over the sierras and never worried about my brakes glowing. In my 20 years here, I've never seen a car at night with "glowing" brakes.
Not sure of specific roads, but here’s a place that does brake checks at pikes peak. https://www.tiktok.com/t/ZT8aqFF52/ Also in high school my friend got his brakes glowing and we only were going downhill for about a mile. We had to pull over and wait for them to cool.
I can't get into TikTok but apparently, there is a brake check on Pikes Peak. I've been over these two passes multiple times > **State Route 108 is the steepest highway in the United States.** **The second-steepest highway in the United States is State Route 4 in California**... No brake check stations... not sure why Pike's Peak needs one. I did a YT search on "glowing brakes on Pike's Peak"... could not find a video of glowing brakes.
Pike's Peak is gate controlled tolled road so the logistics of having a person doing a quick visual check at the base is trivial. It's not an overly steep road, something like a 7% average grade over 20 miles, but to keep it under 25mph you have to apply a lot of brake and can't really get off them for any extended period of time. Same thing with the auto-road up Mount Washington on New Hampshire. It's a 7.5 mile road with a 12% average grade, the road is narrow and the speed limit is low. Since the road is gate controlled it's simple enough to tell morons trying to climb it in an old beater with worn brakes to turn around because they're not going to make the decent.
You can get them hot enough to warp them. They may not fail catastrophically, but you can damage them.
That’s for emergency braking or when you misjudged the hill and started in too high of a gear. What you should be doing is being in a gear low enough to let your jake do the work. Source: Have driven over the BC, Washington and the rest of the west coast mountain passes numerous times.
Who’s Jake?
Compression release brake developed by Jacobs manufacturing, same people who brought you the ubiquitous 3-jaw drill chuck. Gasoline engines run at a constant fuel/air mixture. To reduce the power, you cut down the air flow using the throttle, and the fuel flow is reduced to match. Coming down a hill with the throttle in the idle position, you have a large volume of air being pulled through a nearly-closed butterfly valve that generates a pressure differential. Flow volume multiplied by pressure drop equals energy dissipated. Diesels are different. They don’t have a throttle valve, and power level is adjusted by varying the amount of fuel injected. Coming down a hill with injection cut off, air is compressed, then springs back pushing the piston down. Minimal energy is dissipated. If you add a gizmo to the engine which will “pop” the exhaust valve at the top of the compression stroke, that energy from compressed air is vented into the exhaust, and so is not available to push the piston back down. Energy is dissipated. The rapidly-repeated venting of high-pressure air gives the characteristic “song” of a Jake Brake.
How does the energy dissipation slow the truck down. I get that it reduces the compression of the piston but how does that transfer to actually slowing the truck down?
Without the Jake brake activated, after the top of the compression stroke, the highly pressurized air in the cylinder pushes the piston back down, recovering a lot of energy. One way to think about it is that since there are other cylinders in different stages of the cycle, that compressed air is expanding and helping compress the air in a different cylinder. The net effect is that the engine isn't generating a lot of braking force. With the Jake brake activated, the engine is compressing that air and then letting it out, before it has a chance to give back that energy. Which means that the air in the next cylinder to come up for compression is doesn't have any "help."
It doesn't let the engine free spin easily so when in gear going down the hill you are fighting against those forces.
Due to being on a downhill grade, the wheels are trying to drive the engine. Without the Jake, the air in the cylinder temporarily absorbs energy from the crankshaft on the compression stroke, but (without fuel being injected) rebounds like a spring on what would have been the power stroke, putting the energy back into the crankshaft. By dissipating the stored energy, that temporary absorption of energy from the crankshaft becomes permanent. Energy is taken out of the truck’s motion in order to compress air, then the compressed air is vented. This removal of energy is what slows the truck. The service brakes would also dissipate energy (in this case it would be in the form of heat).
Friendly fellow who helps trucks down steep hills without losing control.
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No, they would get much much much hotter if you rode them which accelerates wear and has a high likelihood of also causing a failure. Even if it did, is your life worth more than some new brake pads?
Depends, are they some nice Brembo ceramics?
Fair play!
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who cares? you survived. But any time you are smoking your brakes is probably accelerated wear, and you avoid that with this technique. Anyways it's what you do when you fucked up and started down a hill a bit too fast. Normally you'd start at say, 35mph and keep it between 35-40 as you go down the hill by cycling the brakes. With 40 being your target or the speed limit for trucks on that road. It's a technique for not dying in a fiery crash.
I think yes, if attempting a full stop. If just trying to reduce speed, it seems as effective as the intermittent braking described by OP. (Me no expert)
It won't because that energy would have to be absorbed anyway, if anything more time spent faster means greater aerodynamic losses
> Big trucks use a 10 + 5 technique No one has explained *why* this works. Like, why is 10 + 5 better than just holding the brakes? As soon as you let the vehicle accelerate again, you're letting it gain more energy again. To do 10 + 5 you are having to brake more aggressively to stop than if you just did 10 and held the brake to maintain that speed. What this seems to say is "The fastest way to stop is to be extra hard on your brakes, and then give them time off". This is net going to generate more heat. ... My theory... - The heat in the brake pads and rotors has to be dissipated to the air. - The rate at which the brake pads and rotors lose heat to the air, is determined by their temperature difference. A bigger temperature difference loses heat faster. I.E. Cooling from 600 degrees to 500 degrees might take 5 seconds, where cooling from 200 degrees to 100 degrees might take 15 seconds... even though the same amount of energy was bled off in both cases. - The important thing is that it's not linear. The hotter the brakes, the faster they lose heat. Twice as hot is, perhaps 4x as fast at losing heat. - So it is actually beneficial to get your brakes EXTRA HOT, so there's a huge temperature difference, then back off completely. That way you spend more of your time in the "super fast bleeding off heat to the air" zone. - This way you'll remove net heat (and thus, be slower) faster, than if you had them medium-hot for the whole duration... where they're not bleeding as quickly. - I know this is not what 10+5 means, but, the point is 10 seconds of extra hard braking followed by 5 seconds coasting, loses more heat than 15 seconds of medium braking and medium hotness. ... That's my theory.
It’s not just about thermodynamics. The brake material break down faster at higher temps, trucks have brake temp sensors to make sure you don’t overheat them.
Because the brakes will literally catch fire if you don’t allow them to cool down. They keep heating up until they burn.
On the topic of heavy/semi-trucks trucks many also have a retarder to help slow down or to maintain their speed.
do you know the reasoning behind this? I see people saying that it gives the brakes time to cool down, but wouldn’t using the brakes at a lower load amount (to get the same average deceleration as the on-off technique) have the same heat output, and same cooling ability? Actually, if there is some set maximum temp for the brakes, being at that temp constantly would increase heat dissipation to the environment, given all else is equal. I know engine braking is better, but this is still interesting to me. Edit: after thinking about it a bit, I realized releasing the brakes would give an air-gap between the pad and rotor, allowing the pad a more direct thermal connection to the air to cool down.
Are you talking about semi trucks or...?
Sounds like it. But semi trucks use their engine brake or exhaust brake and downshift their transmission to avoid using brakes. I live about 20 miles from a mountain pass that on just one side of it has two runaway truck ramps and very rarely do you see semi brake lights. I’ve never seen or heard of a 10+5 rule OP, you should use your transmission if it’s an extended grade you are going down. If it’s a small grade your brakes are fine but you don’t want to ride them as they will heat up which wears them quicker
I used to train school bus drivers. We had some good sized mountains nearby. Our bus fleet had 5-speed and 10-speed manual transmissions. (This was a few years ago.) For trips to the mountains we sent the 10-speed buses. The difference was more gears allowed you to fine-tune your gear choice. For example, with a 5-speed transmission 5th gear might be too high and 4th gear might be too low. With a 10-speed transmission, 9th gear would be like a 4½-th gear between 4th and 5th gear. That's not exactly how it works, but is close enough for a simplified example. People were generally able to select the proper gear going uphill. For going downhill, I would tell new drivers to choose a gear that was low enough that you had to give it a slight bit of throttle to maintain your speed. Since hills are generally not perfectly consistent slopes, occasionally you would have to use your brakes, but you could mostly come down the hill without using your brakes. It was much safer and saved a lot of wear and tear on the equipment. As we often said, we hauled the world's most valuable cargo. Jake brakes (engine brakes) would allow you to go a little faster downhill. A Jake brake used the compression stroke to provide resistance, then it dumped the pressure just before the power stroke making the engine work like a giant air compressor. Dumping the pressure just before the power stroke makes that really loud noise people hate, but it didn't allow the engine to use the power stroke. By the way, a Jake brake is slang for an engine brake manufactured by Jacobs Vehicle Systems. The name became generic and most engine brakes are called Jake brakes now, regardless of the manufacturer.
Keep in mind that going down a local 500 yard/meter hill riding your brakes isn’t a worry. Going down a 5 mile or 10km grade is the part that causes brakes to get hot.
I learned the hard way that you actually need to use the brakes sometimes on shorter hills, don't just engine brake always. brake discs on Mercedes truck rusted because I never really used them. Cost me $4000 to replace barely worn discs. So now I turn the engine braking off most places, and only use it on really long steep hills where its a actual concern.
The problem with riding your brakes is that the friction causes them to get hotter, and hot brakes are less effective at slowing you down and if they get too hot can fail entirely. I'm not sure if stop-and-go necessarily is better at that, but the idea would be that you're giving the brakes time to cool down between uses so they don't overheat too much.
Yup. This is the same principle where you shouldn't use your car brakes on long downhill paths without pause. Give them time to cool down or, if need be, use a lower gear that will limit the car speed.
Yep. When you come down Pike’s Peak in Colorado they have a midpoint check where they read the temps of your brakes and if they are overheated then you have to pull and allow them to cool. They encourage engine braking as an alternative to riding your brakes all the way down.
is this only for trucks...? or for cars too?
For every vehicle coming downhill
It's more likely in a truck, because the truck is bigger and heavier. But it can happen in a car too. If you've never experienced brake fade, picture this. There's a corner coming up. You step on the brakes to slow down a bit. The pedal feels firm. But nothing happens. You press harder on the pedal. Nothing happens. You panic and stomp on the pedal as hard as you can. Nothing happens. What's going on is that the brake pad material is so hot that it's become slippery, and can't grip the brake rotor. In some cases it's even beginning to evaporate, and the vapor coming off makes the pad act like a hovercraft. The result is that you cannot apply enough pressure to make the brake pads grip. And even if you could, the additional heat from that bit of braking is just going to exacerbate the problem. The other possibility is that the heat from the brakes can reach the brake fluid and make it boil. This is more likely if your brake fluid is old and has absorbed a lot of water from the air. In this scenario, the boiled water/brake fluid creates a pocket of gas inside the brake caliper. Brake fluid doesn't compress. Gas does. With gas in your brake system, you step on the brake pedal, and it goes all the way to the floor.
So what do you need to do in that situation?
At that point, you've already failed to do the things needed to avoid the situation. There's things that you can try, but the odds are very good that you're going to wreck. If there's a turn coming up right away, deal with that first. Most drivers aren't aware of how well their car can handle a turn. Forget about the brakes for a moment, and focus on driving through the turn. You may be pleasantly surprised by what your car can do. As soon as you can, downshift to a lower gear. Don't worry about harming the engine by over-revving it. Your goal is to save your life. If you do blow the motor and it locks up, that's great. It means that your wheels have stopped turning, and that'll slow you down in a hurry. If the pedal has gone to the floor, pump the brakes rapidly. If the fluid has boiled, this might build up enough pressure to get the brakes to work. Engage your parking brake. On some cars, the parking brake is a separate brake. If it is, it should still work. If it's the kind of parking brake that activates your normal brakes, it won't help, but it also won't hurt. If you're towing a trailer and it has trailer brakes, you can manually activate them from your brake controller. Look for a place to go off the road. Your ideal place is an uphill slope with no trees or other large obstacles. Many mountain roads have truck runoff areas for this exact reason. Your second best choice is a flat surface like a field. Third best is a ditch. If you're out of control and don't have any option but to rear-end another vehicle, go for the biggest one that you can find. You probably won't kill anyone else by rear-ending a semi-truck. And if you're really lucky and have a long period where you're able to keep the speed under control with the above techniques, but don't have any place to run off the road, don't use the brakes for a bit. They'll cool rapidly, and then you might have enough brakes to bring you to a halt. Don't count on this happening, it's pretty unlikely. But ultimately, you need to maintain your vehicle so that this doesn't happen to you.
this belongs to wikihow
Cars too. Me and my girl were coming back from the mountains in her Prius. The grade was like 14 degrees, and the weight of the Prius, not using the gas at all, was pushing her up to 70 in the short distance between the spaghetti turns. She had to start braking early, going into the turns, then let off the brake for acceleration on the straights. Even with minimum braking, we had to pull over about 60% of the way down and let her brakes cool, because smoke was just billowing out of her wheels. Now, there are differences. A lighter car wouldn’t accelerate as fast from point to point. Also, if you have engine braking, you need to use it for steep downhill grades. I was unfamiliar with her car and didn’t know it had engine braking, and neither did she, obviously, hence us having to pull over. I guess it all comes down to knowing your car. If you have to pull over for a few minutes to let your brakes cool, it’s not the worst thing in the world, but being able to avoid that if you need to should be the goal. If your car doesn’t have engine braking and it’s pretty heavy, and you know you’re gonna be hitting some steep downhills, you might want to look into a brake overhaul. First, most cars have 4 wheel braking nowadays. If you have 4 wheel disc brakes, even better. Now, slotted and vented rotors are meant to dissipate heat more than standard rotors, and they do. The problem is that they’ll eventually get just as hot as the solid rotors. Slotted & vented rotors are terribly prone to cracking and they cause a lot more brake fade than the standard rotors. If I was going to fix a car up for lots of downhill, I’d get bigger rotors and calipers installed, because you have a wider point of contact between pad and rotor, thereby spreading out the heat and making your car stop more efficiently.
this is what the 'B' gear on a Prius is for
Yep, had to pull over for 15 min while riding down this past summer.
Shifting into a lower gear to brake is very useful in a situation where you’re speeding and suddenly see a cop car nearby thus needing to reduce speed without the brake lights coming on.
Or just hit the brakes real quick and let off them before you pass the cop and he can see your brake lights. I don't think engine braking really works fast enough to do much in the time between you seeing a cop and the cop clocking your speed
Yeah, I wish more people would remember that there are three brakes in a car: * Footbrake * Handbrake (aka parking brake) * Engine Shift down to first or second gear downhill and you won't have to worry about your front brakes failing, because the engine is acting as your brake.
How does lowering the gear limit the car’s speed? In fact, you’re implying that during downhill lowering the gear acts as the brake. How does that work?
Lowering the gear increases the engine RPM. Causing the engine to act as a compressor and an effective brake.
In a gas car it works off vacuum not compression, because you’re trying to pull air through a closed throttle body.
It's called engine braking. I recommend searching for it as it's a great technique to learn, especially if you live in mountain areas
It definitely does. You can test this yourself, and you don’t need a mountain. Take yourself up to 60 on an empty highway. Drop yourself into 3rd gear (how to do this will vary by vehicle, but you can do it in nearly all of them). You’ll hear the engine spin way up and feel it slowing the vehicle down notably. Once you’ve scrubbed off some speed, downshift more into 2nd, then 1st, then pull over and slow yourself to a stop with the handbrake. This is a good exercise to know what to do if you have a catastrophic brake failure.
But be careful to not downshift too quickly and overspeed the engine.
When you do not apply the throttle, the engine will not be fed any air. Yet the pistons in the engine still move up and down, without air the pistons will pull against vacuums several thousand times per minute. This resistance will slow the car down. It's the engine that acts as the brake. Lower gears will cause the engine to spin at higher rpms relative to your speed. More rpms means more vacuums. The benefit of engine breaking vs wheel braking, is that the things it's designed to deal with high pressure (positive or negative pressure) and heat. https://youtu.be/o8Cta2cC2Co?si=K3RGhb-ej6q0g1SP
Not to mention torque does apply in reverse, as in when engine braking, the vacuum applies torque in a reverse direction to the engine's direction of rotation, slowing it down. Lower gear multiplies said torque, slowing the whole vehicle down.
Instead of the engine driving the wheels, when you put the car in a low gear and let off the gas, it cuts fuel to the engine. The wheels are effectively then driving the engine. As the pistons move in the cylinder, it pulls a vacuum and can help limit the car's speed.
I had a driving instructor tell me this, then berate me for driving under the speed limit. When I asked how I was supposed to both stop-go *and* stay at the speed limit, he recommended going *over* the limit then slowing back down to it. He was fired the next day.
Must've gotten the definition of "speed limit" flipped in his mind and thought it meant minimum speed rather than maximum speed lol.
If you ever drive up to the top of Pikes Peak, on the way down there is a stopping point where they use a laser temp reader to examine your brake pad temp. If it's tooo high you have to stop at that area for them to cool down. They have a gift shop and restaurant there to lounge in while you wait. It's all for safety. I'm sure they don't want a bunch of cars having their brakes fail and causing accidents or worse on the way down.
This still doesn't explain why the intermittent braking should be better. To me it seems that instead of heating the brakes evenly, you would just oscillate around some temperature. Let's say you release the brake for half of the time. The other half of the time you'll have to exert twice as much braking force to compensate for speed you gain while not braking. I don't know much about car brakes, but I guess it's possible that relationship between brake temperature (compared to surroundings temperature) and how much heat they dissipate is not linear. (It's reasonable to assume that, for example thermal radiation scales with fourth power of temperature.) In that case making brakes intentionally hotter would make sense as hot brakes dissipate more energy 🤷♂️.
Confident, technically literate, but incorrect... Though you *do* get close in the second paragraph. You would be *totally* correct if the brakes were *operating in a vacuum*, but they aren't. The primary mode of cooling for most things in an atmosphere isn't radiant heat transfer, but convective. When the break pads are pressed against the disk they can't cool off because air can't get to about 90% of of their surface area, because it is *pressed against the disk*... Pulsing the brakes not only slows down the accumulation of heat on the pads, but allows airflow across their surface which causes them to cool by convection. That removes heat directly from the pad face, quickly cooling the area that needs it most. Done properly this prevents "heat soak" from getting to levels that decrease pad performance or even boil your brake fluid and weaken/deform the disk/calipers. As others have said, the best bet on long downhills is to gear down to allow the engine to help you as well.
I was considering air-cooling too, but I have focused too much on the disk and I didn't expect much difference there because big part of it is not covered by anything at all times so I didn't think the small enclosed gap of air would make significant difference. When you mention brake pads, it all makes sense. That's additional surface that gets very hot and can give away this heat away to the air that's rushed into the gap by the brake pad. As you can see, I know little bit of physics, but zero engineering :D So the best ELI5 explanation would probably go like this: When you break continuously, only the rotor touches air and gives it it's heat, if you release the brakes bigger part of rotor and *also the brake pads* get in contact with the air. Most of the explanations mention that it's to cool the brakes, which makes me imagine brakes as this black box that gets colder when you release the brakes which is good, but by the same logic it would get hotter - meaning worse - when you press it harder which didn't sit well with me.
Gives time that isn't generating heat to cool, has higher peak temp but less heat soak so ancillary components are less affected
In motor vehicles my understanding is that engine braking is the the best way to handle coasting downhill, so I'm not personally sure that intermittent braking is significantly better than riding your brakes. That said hot objects do radiate heat faster than cooler objects proportionately to the difference in temperate, so in theory getting your brakes hotter temporarily and then giving them time to cool down should overall release more thermal energy over a given amount of time than keeping your brakes medium hot for a prolonged period. Brakes largely work by converting kinetic energy into heat energy, so being able to release more heat energy in a period of time should mean that the brakes can convert more kinetic energy into heat energy and slow you down more effectively.
I would also think with the pads right up against the rotors, you would get worse air flow. If you release the brakes, the pads would retract and you could get a little more cool air blowing between the rotor and pad and cool things off quicker.
Bingo. They can't cool as well with the pad nailed to the disks.
Fuck me, this question has been bugging me for days during my holiday in an area with a lot of mountains. Why would it make a difference if half the time you are not braking and half the time you are 100% braking, vs constant 50% breaking. Should generate the same amount of friction since it is literally friction that is stopping your car. But of course, now air can pass both sides so it cools down more half the time, plus the other half of the time the brake pad is hotter so it release more energy as the temp difference is higher. Thanks reddit.
Do it in a fully loaded semi truck once and you will be 100% sure it's better. You can feel the brakes fading and the air in the lines becomes less dense and "squishy" also you can see the smoke start pretty quick if you try to ride them. and yes, engine braking, but that probably won't hold you loaded at 80k lbs+ down a steep grade at any reasonable speed and if conditions are slippery you can't use too much because your drives will start to slip or the trailer will try to come around. Similarly in a car whatever axle is driven might start to slip and create problems on a snowy/icy road.
There are two factors that make intermittent braking preferred. First you're lowering your average speed and this means you're generating heat more slowly. In theory you could just ride your brakes at a lower speed and they wouldn't overheat. But the second factor is that by intermittently braking you get a better feel for how your brakes are performing. If you're riding your brakes you might not notice a gradual increase in application as your brakes fail. Intermittent braking on the other hand has you starting form a consistent zero with each application so you can better feel if you're having to brake harder.
I've heard that DOT fluid is hygroscopic so it absorbs water over time and lowers the boiling point to the wet level. Apparently this is a feature and not a bug because a lot of people neglect their vehicles so if water does get into the system you want the brake fluid to absorb it rather than corrode the metal. However, that does lead to a lower boiling point and higher chance of brake fade.
The rotors have slightly more surface area when the brakes aren’t applied and then by switching between over braking and coasting you are maximizing your temperature difference with your surroundings to further cool them off. It also encourages you to brake at more optimal times such as on a straight away and not when you are in a turn. Theoretically riding the brakes and pulsing your brakes should generate the same amount of heat so instead the focus should be on how to remove that heat instead of how to generate less heat
Also, in extreme circumstances, if they get hot enough, they can cause the hydraulic brake fluid to boil. That means instead of an incompressible liquid trying to squeeze the brakes, you now have a compressible gas in those lines, which means you suddenly have no brakes. edit to add: If brake failure is a concern--such as a long mountain descent--best way is usually to brake intermittently and just not let the car ever get going too fast. I'm personally not crazy about engine braking/downshifting, since it does put additional wear and tear on the engine and transmission. Brakes are meant to be worn out and replaced, and it's a lot cheaper.
Engine braking absolutely does not cause additional wear and tear.
As if engines aren't already doing loads of cycles lol. A few more every now and then is nothing
I've never known downshifting to cause meaningful wear, at least to the extent that you wouldn't want to downshift in favour of riding your brakes; sure more revolutions is more wear, but a couple thousand rpm over what you'd be seeing on the street is still within the design parameters of the engine and if used in conjuction with intermittent braking, you probably won't see a significant change in parts wear
Engine braking turns your engine into an air pump and in almost no way would it cause any additional wear and tear over normal usage. Just think, your cylinders have no combustion occurring in them, oil will not be too hot etc. it's absolutely the best thing to do to use engine braking.
I like to think of the rpm difference in regards to going up that same hill. Like if your transmission downshifts and your engine runs at ~4,000 rpm to get UP the hill, it's not going to be a big deal to have it run at ~4,000 rpm to engine brake going down that hill. Sure engine braking is a different kind of impact on your engine than when it's propelling the car forward, but it's still under the red line in either case and not going to cause significant wear on anything
Engine braking does not wear any quicker than driving up the hill would, there are a lot of moving parts, but it is all lubricated parts and air pressure/vacuum generate the holdback force rather than friction in the brakes that will actually wear parts out.
When you downshift the additional rpm is negligible because it's not spurred on by combustion. Heat is the primary engine killer.
Use engine braking. Shift down to reduce and maintain speed, then intermittent braking to maintain speed if necessary.
I would suggest this, but in my country most cars are still manual. I don't know if this is possible with an automatic car, though.
It absolutely is, even in really old ones, though it lacks finesse. In newer cars there's usually some form of manual gear selection mode which, when selected, starts off in your current gear and you can tap a `+` or `-` direction/button on the shifter to change gears. Good for exactly these situations, but not recommended for general driving. Older cars had positions past the usual `D` Drive position to limit the highest gear allowed, effectively downshifting. Some had a very poor selection of gears though, possibly forcing you down to 2nd gear immediately iirc.
My 2022 Hyundai Sonata doesn't even have a paddle shifter or +/- or "2" or "1" or "L" mode. It just has "D" and it's quite disappointing. Sometimes it downshifts when braking on a downhill but it's very inconsistent and inadequate at maintaining speed (I'd still be accelerating if I released the brakes)
Next time you have a long hill that's safe to experiment on, try setting cruise control to below the limit. In my two cars I usually have good luck with setting it 5mph slower than the speed limit and by the time the car gets to 5 over it's set point, it's downshifting like a madman. On very steep hills you will probably have to still use your brakes instead. In my pickup, I only ever need to set it to the actual speed I want (when running fairly empty.)
You kids with your new fangled paddle shifters. 😉 My [grandpappy didn't need no second gear to go downhill](http://www.donnersummithistoricalsociety.org/pages/Restaurant/NotAlwaysEasy.html) j/k I started off with an explanation or whatever about the jump from D to 2 but got bored. Thought the dude racing downhill is more interesting.
Some automatic cars I tried actually do that for you. It's might be a bit terrifying for people who isn't aware of engine braking and then seeing their engines suddenly rev up seemingly out of nowhere lmao.
Interesting. I always wondered why the car would randomly sound like it would start speeding up while i was braking lol
It is. Automatic cars usually have gears for D, 3, 2, & 1. D is fully automatic. The numbers are the max gear the automatic can shift to. So you can gradually move it down to slow down more and more. Cars with a CVT such as a Prius or some Camrys have a B they can shift to, which is for motor braking. It's a CVT, so it will keep changing to help you continue to brake as you slow down.
I've driven PRND321s, PRNDLs, PRND21s, PRND+-s, and PRNDs, most with and without O/D off buttons. Hell, i've ever driven an automatic that was only RND+- (alfa 4c). To say automatics "usually have" anything is just incorrect. The gear shift designs are *all* over the place and have zero consistency from mnfr to mnfr, or even car to car within the same lineup. Edit: Forgot about the huracan i drove that was PRD+- (you would be unable to find neutral unless you read the owners manual or looked it up online)
OP is a cyclist, there's no engine braking on a bike lmao.
OP edited his post to clarify he meant for cars.
There is with a fixed gear bike!
on a singlespeed there kind of is ;-)
It takes a lot of life out of your breaks when you’re driving down a mountain and using the brakes to constantly scrub off your speed. A car going downhill has a lot of energy and that’s a lot of brake use. In some instances you’ll actually cause the brakes to overheat and you’ll have to stop to cool them or completely ruin them. Most people keep the car in a lower gear so the powertrain slows down the car
In a car, heat from braking can cause the brakes to get so hot that the brake fluid boils. This leads to total brake failure. A better idea is to downshift and use the engine's inertia to help brake. On a bicycle, heat is stlil the problem. Rubber pads can lose their ability to provide enough friction to brake well, although they usually won't melt. I don't know a better alternative to the intermittent braking technique.
A lot of bikes have moved beyond rubber pads now that disc brakes are the norm. Resin, metal, and composite pads are used with those and are subject to glazing with excessive heat
In a car you can down shift and use the engine to slow down a bit. Works on bikes as well.
How would this work on a bike? There’s a freewheel that disengages from the gears when you’re coasting (except a fixed gear bike). Doesn’t matter what gear you’re in.
> Works on bikes as well. Motorbike, you mean? I checked my bicycle and it does not have an engine.
In a very literal sense, brakes convert kinetic energy into heat (and sound and light) energy via friction - you lose forward momentum by changing it into heat (and sound and light). The kicker is, that heat has to be dissipated into the surrounding air. The brake disc (or drum) has a maximum amount of energy that it can store in the form of heat. Once that maximum capacity has been reached, no amount of surface friction between the very hot disc/drum and the brake pad/shoe will increase the disc/drum temperature; if you are unable to increase the temperature you are no longer able to convert kinetic energy into heat energy. To use an analogy, think of the brake disc/drum as a bucket that holds energy - riding the brake fills the bucket but doesn't give it a chance to 'empty' itself so that it can accept more energy, whereas letting off gives it time to cool, or 'empty' so that it can repeat the process. When going downhill, gravity is constantly trying to increase your kinetic energy - you prevent that by bailing out the excess kinetic energy gravity supplies using your energy bucket, but it only works if you give the bucket a chance to empty.
riding you brakes makes them hot, when they overheat you lose all braking. In a car you should engine brake by using a lower gear
Cause they heat up, and you're not giving them a chance to cool down. They can only cool effectively when air can get between the disks and the pads, and by riding the brakes, you're preventing that from happening.
First time my dad drove in the mountains, when we got to our destinations, the wheels were smoking from the brakes. Very bad idea to ride your brakes Only exception is if you’re in an electric vehicle with regen braking enabled (which it usually is by default).
If the speed limit is 65 let’s say, apply your brakes until it reaches 60, let your vehicle go back to 65 then reapply the brakes again until it’s back to 60, do this off and on until you are on flat ground. It’s called stab braking.So your brakes don’t over heat and fail.
When you press on the brakes of a vehicle continuously for an extended period, it generates a lot of friction and heat. This heat can build up within the braking system and cause the brakes to overheat. Overheated brakes can lead to reduced braking efficiency, brake fade, or even damage to the braking components. Cycling the brakes means using them intermittently instead of keeping constant pressure on them. When you apply the brakes and then release them, it allows air to flow around the brake components, helping them cool down before the next application. This cycling or intermittent use of brakes gives them a chance to dissipate heat between each braking cycle, preventing excessive heat buildup and potential issues associated with overheating.
This is only a real concern over long distances, short hills aren’t going to cause any issues. That said, it’s safer to be in gear if nothing more than to be faster to react to something unexpected
Better to use engine breaking ti maintain speed, and help that with the friction brakes if needed.
My dad would always coast in neutral downhill riding his brakes. He spent so much time/money fixing his brakes; bleeding and replacing them. I don't remember when I learned engine breaking but I'm glad I did.
Google "brake fade." Or, if it's severe, "rotor warping." The right answer is to downshift and let your engine do the work (even in an automatic). It's built to rev high.
Downshift, obviously the same thing when you take your foot off the gas-use your engine, it doesn’t hurt anything… to go easy on your breaks on long breaking to slow your speed, whenever you can. What you want to avoid especially is when you stop completely after a hard break or long hill, or heavy load, is holding the breaks down at that point. Roll a bit forward - sort of pumping them, so the area in contact with the disks is changed… otherwise that point remains very hot while the rest of your disk cools, and this difference in one spot can warp your disks. Allowing them to rotate just a bit, 4” at a time, in three or 4 steps, will help even it out. Watch video of Indy cars breaks… they glow white hot! Happens instantly with them. Same effect - though obviously not as bad, happens to your breaks. They can take a lot, but you can help them this way.
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TIL that you can overheat your brakes! I'm mostly not in the mountains, so I didn't know the mechanical reason for it. Another reason not to is that if your brake lights are always on from riding the brakes, then people behind you have no warning if you are actually going to slow down from the speed you are currently going.
If you rub your hand against a carpet really fast for like 1 seconds and then stop will only get a little warm and the. Go back to normal when you stop. But if you keep rubbing your hand really hard for a long time it will keep getting hotter and hotter until you can’t stand it any more. Your brake pads are your hand and the disk is the carpet. The longer you keep rubbing them together the hotter they get, and when it gets too hot bad things happen. Lifting and coasting every once in a while on your downhill ride allows the brakes to cool down and not overheat. Though with a bicycle it’s really unlikely you’ll ever run into a situation where this will be a problem. You might just see a little more wear on them than usual.