Emergency Stop..

Minstadave said:
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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My car has this. It's really quite alarming how quickly it stops when you mash the pedal!
 
The vast majority of drivers aren't driving Gods like ourselves and in the event of a situation requiring an emergency stop they will just attempt slam the pedal through the bulkhead. That's when ABS helps.
 
In a straight line on an even road surface with even tyre wear, even brake wear and excellent reflexes: without ABS. For all other situations: with ABS. Ideally you want all the braking technologies, in which case mash the pedal as hard and fast as you can, and steer out of the way.
 
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Pedal 100% to the floor in an emergency stop, and let the ABS sort of the grip. I've had plenty of situations where I've had to stop quickly on wet and loose surfaces driving a large van, and it's impressive how quickly ABS gets 3.5 tonnes to stop.
 
I've never had to do a real emergency stop in my five years of driving and don't have abs. I've always thought it was best to pump (i.e.skid) steer pump steer. However you stop much quicker when you're not skidding so I assume the quickest way for me to stop is to find the sweet spot in terms of how much pressure I should put on the break peddle without locking up (also enabling me to steer)? I might do a few emergency stop practices today...
 
I always understood that the point of ABS (other than being able to steer when braking) is that it took the wheels to the point of losing friction and then re-applies the brakes. Effectively cadence braking several times a second for optimum braking by keep traction (and not skidding).
 
Full braking, and use the ABS. I'd encourage you (somewhere safe of course) to try steering under ABS to understand the difference it made. Years ago I was given a morning of driving on an airfield, and one of the things I did was a 50mph > 0mph slalam course both with and without ABS to demonstrate the point - hugely educational (and fun!).
 
Freefaller said:
I always understood that the point of ABS (other than being able to steer when braking) is that it took the wheels to the point of losing friction and then re-applies the brakes. Effectively cadence braking several times a second for optimum braking by keep traction (and not skidding).
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In order for the ABS system to notice the wheel is loosing friction it has to have lost friction. ie be turning slower than the rest of the wheels. - I think.
 
Modern ABS kicks in before the wheel locks fully, ie at just the point the wheel slows turning below the speed of the vehicle.

Older ABS would just cadence brake as the wheels locked.

ABS is less effective in an emergency stop but it allows you to retain control of the steering as in most cases being able to avoid a hazard is better than just straight line braking.
 
Much as I like to think im calm and collected when conducting an emergency stop, the general procedure is pretty much always the same....stand on pedal, clench bum, swear loudly.
 
The biggy is even with the brake peddle jammed to the floor for all you're worth, ABS allows you to still steer the car and keep control which is a life saver. Cadence braking was quite a common practice before the advent of ABS.

Locking the wheels means you've lost steering control and the car carries on in a straight line from the point where they lock.
 
OP you seem to be making a couple of assumptions about braking and ABS systems in forming your opinion...

1. That optimum braking is achieved with zero slip
2. That ABS systems work by causing a wheel to completely lock then releasing it, rinse and repeat

Both aren't correct - optimum friction between the tyre and wheel for braking occurs with a certain amount of slip, just like optimum cornering grip occurs at a certain amount of sideways slip (slip angle).

Modern ABS systems react on the deceleration of the wheel well before it fully locks locks so can keep the tyre close to the optimum amount of slip. Essentially a modern ABS system can keep all four wheels individually at the point of threshold braking. No human, even the best racing driver in the world can match that.
 
Conscript said:
Much as I like to think im calm and collected when conducting an emergency stop, the general procedure is pretty much always the same....stand on pedal, clench bum, swear loudly.
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You missed out press horn and express feeling towards other driver :p
 
Liampope said:
OP you seem to be making a couple of assumptions about braking and ABS systems in forming your opinion...

1. That optimum braking is achieved with zero slip
2. That ABS systems work by causing a wheel to completely lock then releasing it, rinse and repeat

Both aren't correct - optimum friction between the tyre and wheel for braking occurs with a certain amount of slip, just like optimum cornering grip occurs at a certain amount of sideways slip (slip angle).

Modern ABS systems react on the deceleration of the wheel well before it fully locks locks so can keep the tyre close to the optimum amount of slip. Essentially a modern ABS system can keep all four wheels individually at the point of threshold braking. No human, even the best racing driver in the world can match that.
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Well now I know, which was one of the points of me starting the thread.
Thanks to all for your contributions.
 
I had to emergency stop in an ABS-less Fiat once on a wet road because somebody stalled as they were pulling out. It was quite scary, I was going about 50, slammed the brakes on and could hear the wheels skidding straight away but in that slow motion few seconds I thought just holding the pedal would be best.

Luckily the kid in the car manages to start up and move before I skid into him, he'd have been mashed up pretty bad if he hadn't.
 
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