Engine braking vs ABS on icy roads.

[Savij]

Which one is better for traction and control? I'm not talking about clutch wear or anything like that, just controlling the car.


I was talking with a guy at work about this short, icy (when it snows) section of road that's pretty steep with a sharp curve near the bottom. He said you should always engine brake on any icy hill. I am of the opinion that you want to avoid using engine braking since you get less control, and are more likely to lose traction compared to just using the brake pedal. I don't see the point to using it on a short little hill where there is no chance of overheating the brakes.

If you have a FWD car I can picture the rear end getting unstable and sliding out since only the front wheels are slowing the car down. I could see a RWD car as being a little bit better with engine breaking on the straight part of the hill since at worst the rear end will lose traction but won't be trying to go faster than the front on the straight. Even then, it's more likely to lose traction than using the brakes.

I can't comment on an AWD car trying to engine brake since I'm having trouble figuring out how the "power" would be routed when the engine is trying to slow the car down. I suppose this one could be ok since the AWD might act like an ABS system and transfer "power" away from the wheels that lose traction.

Am I missing something? Is there any situation where you would want to use engine braking to slow the car down when the normal brakes work?

 

[thomsbrain]

A FWD car is more likely to understeer in this situation than oversteer. You're taxing traction at the front wheels by engine-braking, while the rears are left to devote maximum traction to lateral forces. RWD is more likely to oversteer.

I think you'd probably get the best braking performance by using ABS brakes (especially with modern brake force distribution) and leaving the car in neutral. People sometimes recommend engine braking because it is very light and progressive and prevents you from jamming the brake pedal and locking the wheels. With ABS, that's not so much of an issue anymore.

Regarding AWD systems or cars with limited slip differentials, it would depend on the design of the differentials. Some differentials are designed to balance wheel speed under engine braking (would help make things stable), and some are not, depending on the handling needs of the car when they were designing it. I would expect that most FWD cars with LSDs do not use the limited-slip function under engine braking because it would increase understeer while slowing down, which is a negative trait that already affects FWD cars. They are usually doing everything they can to reduce understeer rather than promote it.

 

[Zenmervolt]

ABS, if invoked, lengthens stopping distances in snow, ice, gravel, and sand. You should not count on it to stop your car quickly. However, the huge benefit is that you retain a greater amount of control (regardless of advertising claims, even with ABS, some control is lost when the system is invoked) and in most cases this is preferable to the shorter stopping distance offered by locked brakes.

In your scenario, I would still advocate engine braking if possible since it encourages a driver to keep speeds low in those conditions if it is to be useful. The biggest problem with things like ABS and traction control is that people think that these aids make them invincible, which actually tends to result in people getting into minor accidents that would have otherwise been easily avoidable.

ZV

 

[spidey07]

The only problem with engine braking is on very slick conditions is you can actually CAUSE wheel slippage and severe loss of traction. Now it takes REALLY slick roads to do it but I've done it plenty of times. Basically traction is so minimal that the compression of the engine actually overcomes traction and your wheels move slower than the road. To compensate you need to be in a higher gear but you may be moving too slowly to be in that gear. In that case you'll have to control your wheels with the clutch.

 

[LTC8K6]

I was taught to always brake in neutral on ice. It has always worked well for me.

In gear, the drive wheels always seem to lock up on ice and then you are along for the ride.

In the scenario given, you need to be able to turn, which is a crapshoot on ice no matter what. Have good snow tires and hope the ABS will let you turn, I guess.

If you are talking about actual ice, as in a glazed over surface, all bets are off.

If it's just snow and slush, or rough ice, a competent driver should be okay whatever the car.

 

[bruceb]

I think engine braking would be better for most cars. And on ice or snow, I always try to anticipate upcoming turns, so I can very gently ease the steering into the turn. It is not a guarantee you won't slide, but it does lessen the chance of it. Same for braking, try to anticipate it and very gently on the brake pedal.