Viewing 40 posts - 1 through 40 (of 94 total)
  • Engine Braking?
  • walleater
    Member

    I live in an area that can get very snowy / icy in the winter. There was a predictable on-line argument recently with everyone telling everyone else how to go down hill in these conditions. Common practice is to gear down, but someone who claimed to be a winter driving instructor stated that when engine braking (assuming a 2wd car I guess but I don’t know as I didn’t get involved in the discussion), the force is only acted on one wheel, unlike braking. Is this true and does anyone have a definitive link to show this? I’ve tried looking it up and as always it’s just endless opinion and no facts to back anything up (yay internet!).

    kerley
    Member

    It will be acted on both wheels but the diff may mean it is not a dead 50/50.

    Premier Icon Cougar
    Subscriber

    I guess it’s the same principle as accelerating. You’re applying power through a differential, so if one wheel spins then there’s no power getting to the other one. So with engine braking you’re applying a braking force to both wheels so long as one of them isn’t sliding.

    Premier Icon Stoner
    Subscriber

    A traditional differential will result in only one wheel receiving driving force, then one might assume that if the engine is acting as a retarding force rather than a drive force, then it too, acts only on one wheel.

    In drive, when one wheel loses traction, “all” drive force goes to the spinning wheel.

    Engine braking, when one wheel locks up, say, Im not sure what happens to the other though! Brain going fuzzy…

    Premier Icon Cougar
    Subscriber

    … in any case, engine braking will only apply to (usually) the front two wheels, where as the middle pedal goes to all four.

    Plus, y’know, ABS. It’s not 1980 any longer.

    Premier Icon Cougar
    Subscriber

    A traditional differential will result in only one wheel receiving driving force

    If that were the case we’d all be driving in circles.

    Flaperon
    Member

    Engine braking in icy conditions seems mad to me. Foot brake, and if any hint of loss of traction, clutch down.

    It’s like the advice to pull away in second gear. Why? It’s not like you need any less torque to move away from a standing start in 2nd than 1st.

    Premier Icon maccruiskeen
    Subscriber

    If that were the case we’d all be driving in circles

    we do anyway – otherwise we’d never get home

    Premier Icon ta11pau1
    Subscriber

    Descending hills in a lower gear, means higher revs and more engine braking, which controls your speed.

    That’s why it’s a good idea. Because your speed will be lower, you need less actual braking which means less chance of locking up/losing control.

    Go down a hill in 4th gear, with no braking.
    Then do the same hill in 2nd gear with no braking. Your speed will be lower the 2nd time.

    Premier Icon Cougar
    Subscriber

    It’s like the advice to pull away in second gear. Why?

    Probably because it makes it more difficult for people who can’t drive very well to accidentally rev the tits off it.

    Premier Icon maccruiskeen
    Subscriber

    Arguably though what you want is control not out and out stopping power.   Using the engine means you’re apply very gentle braking and trying to avoid a situation where any of the wheels are sliding so that the car is more likely to go where you point it. That’s the idea of abs too but under engine power the wheels are trying to turn (and in fwd are turning in the direction you’re pointing them) rather than just being prevented from locking

    Premier Icon Mary Hinge
    Subscriber

    My Volvo xc60 doesn’t do engine braking!

    It has some fancy economy gizmo that let’s it keep rolling.

    So braking it is.

    It has a hill descent button though for when it gets proper slippery.

    Premier Icon scotroutes
    Subscriber

    Gotta be careful though. If you start slowing down sharply by using the engine and not the brakes then you risk a following driver ploughing into you.

    Premier Icon ta11pau1
    Subscriber

    Cars don’t have enough engine braking to slow them quickly, motorbikes on the other hand…

    Come off the throttle in 1st gear on my 1000cc vtwin and it feels like you’ve chucked an anchor out the back!

    But for the OP, engine braking will almost never be powerful enough to lock up a wheel, so it will be acting on all the driven wheels.

    Premier Icon Drac
    Subscriber

    Ooooh! A driving thread.

    Back in a minute off for tea and biscuits.

    Premier Icon jeffl
    Subscriber

    Like people have said above, engine braking will slow the rate of rotation of the wheels down. Where as using the brakes will cause the wheels to stop rotating completely on a low friction surface (ice), thus causing a skid. Then the ABS will kick in and modulate the braking force.

    Premier Icon iainc
    Subscriber

    ^^ engine braking on ice can cause a skid too, which is more awkward than a braking skid in an ABS situation.

    Premier Icon binners
    Subscriber

    Can I raise a practical question at this point?

    How would it work on a conveyor belt?

    Cougar

    Subscriber

    … in any case, engine braking will only apply to (usually) the front two wheels, where as the middle pedal goes to all four.

    Plus, y’know, ABS. It’s not 1980 any longer.

    Anyone who’s ever raced a car with ABS on track will know that it’s not actually very good at stopping you when grip is at a premium. I ended up taking it off one of my production-based race cars years ago.

    JP

    B.A.Nana
    Member

    down steep hills in snow I’ve always let it free in 1st gear and feathered the hand brake. No idea if it’s best practice but always worked so far

    Premier Icon jamesoz
    Subscriber

    Cars don’t have enough engine braking to slow them quickly,

    I’ve had the ‘pleasure’ of driving ’90s non turbo diesel fords when they were new. If you popped them into first and lifted the clutch when nearly stopped they would lock the front axle on a damp road.

    My 951 broke the bellhousing at the gearbox end of the torque tube because of engine braking combined with a paddle clutch and hamfisted driver.

    Premier Icon howsyourdad1
    Subscriber

    *Waves from Sweden*

    Government advice is to use a lower gear and use the motor as a brake. You reduce the risk of locked wheels, or , as they put it..

    Samma grundregler gäller som när du kör på hala vägar i övrigt. Försök att behålla väggreppet och undvik att hjulen låser sig. Moderna bilar har antisladdsystem som gör att tekniken känner av om ett hjul börjar slira. Då bromsar det hjulet in så att kraften och friktionen fördelas på alla de drivande hjulen.

    I utförsbackar är det bättre att köra på en lägre växel, eftersom du då kan utnyttja motorbromsen. Då minskar risken att hjulen låser sig. Det är alltid bra att försöka motorbromsa, både ur säkerhetssynpunkt och ur miljösynpunkt.

    Premier Icon jamesoz
    Subscriber

    I’d go with the Swedes on this one

    Premier Icon jimmy
    Subscriber

    Will a car skid through engine braking on ice?

    Has shades of aeroplanes on tread mills.

    Premier Icon hot_fiat
    Subscriber

    Modern ABS is linked to the throttle and will tickle it open a tad when engine braking if it detects a wheel starting to slip.

    walleater
    Member

    Will a car skid through engine braking on ice?

    Has shades of aeroplanes on tread mills.

    I feared that ha ha.

    My ‘wisdom’ was to engine brake in order to get to a general speed (or lack of), and then fine tune with the brake. But I did slide going down a reasonably steep hill (that others were spinning out on going up, and the road got closed shortly after). I was wondering if it was more the engine braking, actual braking (with ABS), driver, tires or a combination of all that caused the sliding 😀 I kept the vehicle under control by finding deeper snow right by the kerb and keeping the tiyres next to the kerb in the that. It’d be a good road to experiment on if it wasn’t for the fact that you’d crash into oncoming traffic due to it having a bend near the bottom!

    cubist
    Member

    It’s like the advice to pull away in second gear. Why? It’s not like you need any less torque to move away from a standing start in 2nd than 1st.

    In regular comfort mode my car never uses 1st to pull away. Automatic use fluid drive rather than a clutch plate so your not going to burn that out. Its slower to spin the engine up in 2nd so the power is put down smoother. In Icy conditions where smooth acceleration/braking is especially important slower revving makes it easier even in lower power cars.

    Premier Icon molgrips
    Subscriber

    So the point about engine braking is that it applies gentle braking force to the front wheels and they never actually stop, so in the old days this was a nice way to slow gently on ice. However you can’t really control the braking force very well, so you could still have one wheel slip, and if that happens you’ve suddenly got nothing. Also, all the braking goes through the front wheels so they have to do twice the work, meaning they are more likely to slip in the first place. All it does is apply retarding force to the wheels same as braking, but it’s uncontrolled and only on two wheels. So a bit of a bad idea really.

    With ABS, the car applies braking force to all four wheels, and it modulates them independently i.e. if one skids, it reduces the force on that one until it grips again – the others are unaffected. It is possible to be unable to stop even with ABS, but this means that there just wasn’t enough grip to slow down any quicker.

    The flaw with ABS is that if all four wheels lock, the car thinks you’re stopped, so it does nothing and you slide on. However, with modern cars they have ESP which means it knows you’re still moving, and in which direction, so it can continue to modulate the brakes to maximise grip. This doesn’t mean that you will always be able to stop, of course – there is a limit to the available grip – ESP just maximises it better than you can as a driver.

    The reason you need to turn ESP off on a racing track is that you are not trying to stop, you’re trying to corner, and a certain amount of slip is desired by the driver and it needs to be predictable. And you can’t predict it with the computer controlling the brakes for you. I think some racing cars have ABS but I’d bet it’s set up rather differently.

    superfli
    Member

    I’ve spun a car numerous times through engine braking (on a track). Any sudden change in velocity or direction will cause an in balance and possible skid.
    Not saying what’s best, just avoid a skid

    submarined
    Member

    Having had a DC2 Integra and an FD RX7 with lightened flys through multiple Winters, I can confirm it’s a) possible and b) pretty****ingscary to lock up wheels on ice/snow through engine braking.
    Never had it on a car with a normal fly though.

    In response to the original question, jack up a 2wd car without an LS and leave one of the driven wheels on the ground, make sure it’s in neutral, and you can turn the other driven wheel no probs.
    Which logically extrapolates that yeah, one will lock up in the op’s scenario.

    Also, on snow, lock up are better for stopping in a straight line than ABS.

    CountZero
    Member

    Will a car skid through engine braking on ice?

    Yes, if you shift down and just dump the clutch – the trick is shifting down and feeding the clutch in slowly, so there’s no jolt that could unsettle the car; keeping everything smooth is golden. I’ve been using engine braking in every car I’ve owned since I started driving, in the mid-70’s, and I’ve only lost control once, where a junction had flooded then frozen, and I had to turn 90 degrees right. I slowed up gradually coming up to the junction, but as soon as I turned the wheel, the car just carried on until the grass verge stopped it.
    Required some rocking back and forth to get clear, but I could easily have had the car do a 360 and go through the hedge if I’d just used the brakes, I’d got it down to walking speed just using the engine.

    Premier Icon molgrips
    Subscriber

    the trick is shifting down and feeding the clutch in slowly, so there’s no jolt that could unsettle the car; keeping everything smooth is golden.

    But you can brake just as gently. And you’ll get braking force from four wheels not two.

    The brakes are for stopping, the engine is for going.

    submarined
    Member

    The brakes are for stopping, the engine is for going.

    I see this trotted out a lot
    Imho it’s bad advice in areas with big descents. Getting halfway down a hill with glowing, overheated brakes that are starting to boil the fluid because they’ve been dragged the whole way isn’t a nice feeling.
    When I was leaning to drive I cooked my brakes doing exactly that in the bloody South Downs.

    Premier Icon colp
    Subscriber

    @howsyourdad1

    We all know all you said there was CD rack and meatballs

    Also, on snow, lock up are better for stopping in a straight line than ABS.

    That’s true for deep snow (and sand) where you can build up a pile of powder in front of your tyres to create a larger surface area. But 1) most of the snow we encounter here is hard-pack or only a few cm so that doesn’t apply and 2) ABS helps you maintain control of steering as you’re slowing down.

    In modern cars with ABS and brakes that don’t overheat too readily, it doesn’t make any sense to force all your braking to be done via the wheels you also wish to steer with. So assuming a FWD car which most people have, advice to use engine braking is daft. IMO which is of no consequence at all.

    Premier Icon jamesoz
    Subscriber

    The brakes are for stopping, the engine is for going.

    I see this trotted out a lot
    Imho it’s bad advice in areas with big descents. Getting halfway down a hill with glowing, overheated brakes that are starting to boil the fluid because they’ve been dragged the whole way isn’t a nice feeling.
    When I was leaning to drive I cooked my brakes doing exactly that in the bloody South Downs.

    Hence the ‘use low gear’ signs on steep descents.

    crikey
    Member

    Latest VW DSG gearboxes will coast when you take your foot off the throttle, but if you brake going downhill, the engine will brake for you…

    They only make the things, perhaps they know how they should work…

    Premier Icon iainc
    Subscriber

    My auto changes down gears when going slowish down steep hills, so I guess the electronics think that’s wise. Newish Audi Quattro.

    Premier Icon Alex
    Subscriber

    Engine braking in icy conditions seems mad to me. Foot brake, and if any hint of loss of traction, clutch down.

    I have an auto so I feel this advice probably won’t help me, however…

    … I also have a BMW so when faced with ice and snow, the only driver activated control that is of any use are the hazard warning lights. Closely followed by the airbag 😉

    I asked my recently full licensed offspring what they were taught. They both responded with ‘nothign at all’.

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