The ABS discussion thread

[dadu]

You beat me to it, upon reading NeoT's post i could remember reading the same somewhere (poor guy took beating in between) but you found the source, before I could

Originally Posted by Samurai

Just googled for 4WD and ABS, and found these links. It is indeed a good thing ABS doesn't work with 4x4.

http://www.4x4abc.com/4WD101/ABS_parttime.html
http://www.4x4abc.com/4WD101/ABS_offroad.html

[Samurai]

Originally Posted by suman

Samurai, we could be going OT here so I'll stop after this one - ABS prevents a wheel lock-up & it is not necessarily only under turning conditions so I'm not sure I understood.

I was talking about usefulness. If you are going in straight line, it doesn't matter whether wheels lock or not. In fact non-ABS brakes provide faster stopping in straight lines. Only real use of ABS is that it allows you to brake even while turning, a non-ABS brake would lock the wheels and you won't have steering control.

Originally Posted by suman

Also, in 4H mode, you can (and are allowed) to accelerate a fair bit; you could also be engaging it on tarmac (though not recommended for long stretches) so why wouldn't ABS work - or why would it make more of a racket ? Yes, in 4L you would be crawling but 4H?

I think this article has addressed it: http://www.4x4abc.com/4WD101/ABS_parttime.html

Regarding the ABS racket, I was refering to 4H. Actually my experience is from driving cars with ABS in 6-7 inches deep snow. The ABS gets so confused it keeps recoiling like a gun even if you mildly press the brakes.

[suman]

Originally Posted by Samurai

In fact non-ABS brakes provide faster stopping in straight lines.

Not if the wheels lock-up - I've experienced it in non-ABS vehicles so differ with you on that one

About conditions in snow, I dunno - you're the expert, I haven't driven in 6 inch snow yet & whatever little I have hasn't been on an ABS vehicle

[arunforu1]

Yes ABS is of little help in soft deep snow over a hardsurface(eg fresh snow on tarmac/pavemnet/concrete).SPECIFIC CASE

case 1: vehicle with ABS: As soon as you apply brakes, wheels tends to lock-up very quickly & ABS makes pedal recoil very fast(fast juddering) & keeps on juddering untill vehicle stops fully. & belive me the distance is quite considerable as wheels tends to lock-up &slip(due to low coefficient of friction on snow).And ABS prevents it from locking causing frequent rleasing & grabbing of brakes.

Case 2: Vehicle without ABS: As sson as you apply brakes, the wheels locks up obviously at that very moment(due to low coefficient of friction).But in the process they immediately plough through snow surface & make contact with hard ground(with good coeeficient of friction) & stops the vehicle.

Note: In very deep snow its not advisable to drive, as you will fall short of ground clearance before need to put brakes on.

[cheap_deal]

^^ you need good SNOW tyres to drive in areas with heavy snow. All season are crap, i have first hand experience of driving an bmw 330i with dsp, abs etc with all seasons and i was getting outbraked by kia drivers who had abs and snow tyres.

[dadu]

Suman, I have to agree with Samurai here, although having read many articles on ABS and it quoting stopping distance is almost same in ABS/non-ABS vehicles, but still my practical sense does not allow me to believe that.

Its all about physics and friction, the immediate friction (which ABS reduces) between the rubber and road will make it stop slightly faster and hence the screech and burned rubber marks on the road under straight line condition.

You can also do a test, mark a line on a clear straight road and then drive a non-abs car at 20km speed and once you reach that line brake hard for an immediate stop, mark the stopping distance, now try that with a car equipped with an ABS, same make. You'll get the answer.

I also found this :

According to RCMP and Transport Canada research, some ABS work exceptionally well, but others, particularly in some domestic cars, trucks and SUVs, take longer to stop the vehicle - longer, in fact, than conventional brakes under identical conditions.

Source

Originally Posted by Samurai

In fact non-ABS brakes provide faster stopping in straight lines.

Originally Posted by suman

Not if the wheels lock-up - I've experienced it in non-ABS vehicles so differ with you on that one

[suman]

Originally Posted by dadu

You can also do a test, mark a line on a clear straight road and then drive a non-abs car at 20km speed and once you reach that line brake hard for an immediate stop, mark the stopping distance, now try that with a car equipped with an ABS, same make. You'll get the answer.

Errr, it would not be as simple as you would need the same model & make and apart from that, you are relying on the human element in terms of pedal pressure & how hard the brake pedal is pressed - would need to be the same.

Its a ridiculous waste of time & energy and not required IMHO. Lets talk more about this once you've had some practical experiences on non-ABS cars locking up & crashing and ABS cars stopping in time (I've experienced both) - till such tiem it will only be theory & more theory

[csentil]

I don't know if the claim is that ABS will shorten your braking distance. I don't think so. ABS allows you to have control of your vehicle when braking hard. That is what it is meant for.

[arunforu1]

Originally Posted by csentil

I don't know if the claim is that ABS will shorten your braking distance. I don't think so. ABS allows you to have control of your vehicle when braking hard. That is what it is meant for.

Yes ABS will shorten the distance in case of very hard braking, where wheel-lockup is sure(eg hard braking on a wet road).

Simple physics behind it: coefficient of static friction is always more than coeffcient of kinetic friction.

As long as wheel is rolling(not locked up), there is no sliding between road & tire surface & hence no kinectic friction.

But as soon as you puch brakes hard, wheels get lock up & start skidding/sliding causing coefficient of friction(grip) to reduce greately. But in a vehicle with ABS, wheel locking is prevented by ABS system & hence provide more normal rate of coefficient of friction(grip is more than sliding). Hnece the smaller stopping distance , with bonus of control remaining intact.

try it at higher speeds, as at lower speeds, you will hardly manage to lock-up wheels in a non-ABS vehicle.

[tsk1979]

Actually on Tarmac, if your wheels lock up at high speed, the rubber melts. So at that point you are just gliding on liquid rubber.
Thats why when you hit the brakes you get sudden deceleration, but after a little while you don't slow down very fast.
In conditions like off road, dust etc., ABS is very very bad and increases stopping distance

[1100D]

Forget total gravel roads, how effective will ABS be on a road sprinkled with intermittent sand/pebbles/loose tarmac and dry grippy surface (kind of surface conditions we are used to seeing in India). I guess, ABS will release the brake on the sand and not utilise the intermittent grippy tarmac fully for braking. However, ABS wil definitely help keeping the vehicle from spinning out.

However without ABS you would intermittently slip on sand, grab on tarmac. However since these forces may act on one side only at a time, the vehicle may spin out of control.

Most ABS accidents IMO takes place because of an unplaced beleif that an ABS equipped car would save them from any situation.

[csentil]

Originally Posted by arunforu1

Yes ABS will shorten the distance in case of very hard braking, where wheel-lockup is sure(eg hard braking on a wet road).

Simple physics behind it: coefficient of static friction is always more than coeffcient of kinetic friction.

As long as wheel is rolling(not locked up), there is no sliding between road & tire surface & hence no kinectic friction.

But as soon as you puch brakes hard, wheels get lock up & start skidding/sliding causing coefficient of friction(grip) to reduce greately. But in a vehicle with ABS, wheel locking is prevented by ABS system & hence provide more normal rate of coefficient of friction(grip is more than sliding). Hnece the smaller stopping distance , with bonus of control remaining intact.

try it at higher speeds, as at lower speeds, you will hardly manage to lock-up wheels in a non-ABS vehicle.

I'm sorry if my post wasn't clear. What I meant to say was that I don't think car companies claim that ABS shortens the braking distance. As tsk and 1100D pointed out it can even increase braking distance. What ABS does is helps you maintain control over the car by preventing wheel lock so that one can steer.

[Thad E Ginathom]

They would be foolish to claim that it shortens the stopping distance.

But it does matter, even in a straight line, if the wheels lock, because maximum braking efficiency is just before they lock. That is what ABS sets out to maintain. Locked wheels means less efficient braking.

If this was all there was to it, it might even be safe to claim that it decreases braking distance ---- but there are surface conditions, as others have posted, on which it might have the opposite effect.

I think there is a confusion with cadence braking, where the human tries, by fast jabbing of the breaks to achieve the same effect.

I am away from my bookshelf, but IIRC, the UK Police driving manual states that, for emergency stopping in a straight line (my copy would have been written, I think, before ABS was common), not to try cadence braking, but to lock the brakes and skid to a halt.

The human foot cannot do better than this.

But, I suspect that ABS can!

[dadu]

It was the simplest I could think of but all these tests under various conditions are done by the various safety testing agencies around the world and that is when they publish their theory.

God forbid to push anyone into real life situations, but as I posted by someone here, most ppl think it helps them stop faster so they can drive faster and thats when they get into it.

Originally Posted by suman

Its a ridiculous waste of time & energy and not required IMHO. Lets talk more about this once you've had some practical experiences on non-ABS cars locking up & crashing and ABS cars stopping in time (I've experienced both) - till such tiem it will only be theory & more theory

Thats the point, steer away with ABS,in a straight line stop on non-wet paved surface, ABS or Non ABS doesnt make much difference, at high speeds both might not be able to stop in time.

Originally Posted by csentil

What ABS does is helps you maintain control over the car by preventing wheel lock so that one can steer.

thad, It would be interesting to know what the police manual states actually, if you can find and post the contents, thanks.

Originally Posted by Thad E Ginathom

I am away from my bookshelf, but IIRC, the UK Police driving manual states that, for emergency stopping in a straight line (my copy would have been written, I think, before ABS was common), not to try cadence braking, but to lock the brakes and skid to a halt.

[Thad E Ginathom]

Well, I'll be away from home for a while...

Actually, my copy is old and if I spot a more up-to-date one in a bookshop, I might invest (I'm in UK at the moment). It should take ABS etc into account now, and it would be interesting to see.