Emergency Stop..

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Presuming you have ABS:

I've often heard the best way to stop is, "•press as hard as you can on the brake pedal and keep full pressure applied until you come to a stop."


But.... the most friction is gained on stationary surfaces (ie not skidding).
and there has to be a skid (however small) for ABS to kick in, right?

So surely the quickest way to stop is to break as hard as possible without ABS kicking in?


As a complication to that, I guess the rear wheels could be causing the ABS to come on in which case it would be best to keep pressing as hard as possible? Can you detect the difference in ABS working on the front / rear?

Thoughts?
 
Hyburnate said:
Not sure on this but wouldn't repetitive pressing on the brake (pumping it) cause the ABS not to come on? :confused:
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My understanding is that the ABS will always and only come on if the wheels are turning at a speed slower than the car is moving.

"Pumping" would make no difference and is never recommended
 
I was taught to brake as hard and fast and possible.

I got marked down for it on my test! The examiner said the car would have locked up if it hadn't had ABS. I was very miffed about that.. especially seeing as I knew the car had ABS :p
 
ABS doesn't necessarily make you stop quicker. Its purpose is to allow you to remain in control while under heavy braking by preventing the wheels from locking up (If the wheels lock, you cannot steer!)

On a dry road, locked wheels will stop quicker than ABS. On an icy road ABS may well prevent you from stopping at all! (I have had this somewhat disconcerting experience! :eek: !)
 
Orionaut said:
On a dry road, locked wheels will stop quicker than ABS.
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This is 100% wrong. There is less friction on a moving surface. (so the mostly on, slight off nature of ABS would be better than locked)


But that's nothing to do with my question. My question is presuming you have ABS, should you press the brake as hard as possible (forcing ABS to come on) or press it as hard as you can but just before ABS kicks in.

For sake of argument lets say it's a dry road in a straight line but in reality variables like that wouldn't make a difference to my question.
 
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Hard as possible. ABS can break individual wheels, a human can't.

By breaking at limit of a wheel locking up you are limiting the braking effect of the other 3 tyres
 
( |-| |2 ][ $;25401877 said:
So surely the quickest way to stop is to break as hard as possible without ABS kicking in?
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The problem is determining how hard one can brake before the ABS starts working.

Simon said:
Hard as possible. ABS can break individual wheels, a human can't.

By breaking at limit of a wheel locking up you are limiting the braking effect of the other 3 tyres
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This. Often I can feel when a wheel or wheels are about to lock up, but the ABS beats me to reducing the amount braking applied.
 
a lot of cars have brake assist, if you brake hard it depresses the brake peddle to the maximum and lets the ABS get the job done. So I reckon just braking hard is the way to go.
 
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Simon said:
Hard as possible. ABS can break individual wheels, a human can't.

By breaking at limit of a wheel locking up you are limiting the braking effect of the other 3 tyres
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This makes perfect sense to me. Though state for example the fronts are more likely to lock, is the extra breaking gained by the rear enough to counter-act the slight skidding of the fronts?

Rroff said:
In a real emergency stop you'll rarely get to pump the brakes anyhow.
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Who said anything about pumping, I'm thinking from more of a theoretically view. Although yes I accept human error in not pushing hard enough is ruled out by just slamming them on.
 
I had to do an emergency stop today (moron turning right out of a turning without looking right), and I pressed the brake as hard as I could and it felt like a lifetime before the car actually stopped.
 
Simon said:
Hard as possible. ABS can break individual wheels, a human can't.

By breaking at limit of a wheel locking up you are limiting the braking effect of the other 3 tyres
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This is EBD, not ABS, and far from every ABS equipped car has this capability. Does make a massive difference though, really very impressive indeed.
 
( |-| |2 ][ $;25402157 said:
This is 100% wrong. There is less friction on a moving surface. (so the mostly on, slight off nature of ABS would be better than locked)


But that's nothing to do with my question. My question is presuming you have ABS, should you press the brake as hard as possible (forcing ABS to come on) or press it as hard as you can but just before ABS kicks in.

For sake of argument lets say it's a dry road in a straight line but in reality variables like that wouldn't make a difference to my question.
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IIRC, "Optimum" braking is with the wheels rotating at about 85% of the free rolling speed (#) because the contact surface with locked wheels will melt and the molten rubber is actually a lubricant. But in practice locked wheels at any normal speed on a dry road represents pretty good braking and engaged ABS will likely be less effective.

(#) But no ABS will achieve that really.

Back to the original question. I have found that braking on ice is better if you lift off and stop the ABS from operating. I imagine that the same will also apply on non-icy surfaces!
 
Drive a car with decent ABS and might change your view. Although I agree on Ice and snow it is better to have no ABS
 
Orionaut said:
But in practice locked wheels at any normal speed on a dry road represents pretty good braking and engaged ABS will likely be less effective.
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In one of the few Top Gear tests which I feel is actually relevant to real-world use, Jeremy's 72 tonne, rubbish, Volvo 760 with ABS actually destroyed the cars of May and Hammond in a brake test. Hammond's brakes were made of chocolate, but May's Audi just locked up and cruised past the much heavier 760. Locked wheels are good for the camera and perhaps the court, but in terms of actual benefit, there is none for anyone who's able to maintain a degree of rational in an situation (I've been there on a bike).
 
The real advantage of ABS is not that it helps you to stop the car more quickly, but that it prevents the wheels from locking (and skidding) and therefore allowing you to steer while under heavy braking.
 
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