The ABS discussion thread!!

[suman]

Originally Posted by anupmathur

You probably mean 4WD Low Ratio. That is the mode used for 'crawling'.
In 4WD High Ratio there really is no constraint on the speed you should do.
But again the caveat applies that it should be used on roads with some slip.

That is exactly the point I was making a few pages ago -

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.

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?

[Samurai]

Originally Posted by anupmathur

You probably mean 4WD Low Ratio. That is the mode used for 'crawling'.
In 4WD High Ratio there really is no constraint on the speed you should do.

I was obviously referring to 4WD Low, why else would I say crawling?

Originally Posted by suman

The problem with this thread is that most people (please note bold highlight under most) commenting are being theoretical & will throw various articles & links at you without actually having experienced it in real life. Pointless getting into futile discussions with them so I'm out of this thread. To me, ABS is like - a no-brainer!

Hope you don't count me in that most , I have driven alteast 100,000miles (160,000Kms) on ABS enabled cars. At least 20% of that in snow and icy conditions.

I would take ABS over non-ABS anyday. I am only trying to stop the overhyping of ABS. This is from another thread:

Originally Posted by Samurai

Talking about misconceptions, one should also be aware that in the slippery conditions ABS only helps the driver retain steering control, it won't manage to stop significantly better if there is no friction. If there is no way to steer into, results will be same. Actually there have been lots of cases where ABS equipped drivers have steered fatally into oncoming traffic or jump off bridges (bridges become iced faster than regular roads) where as non-ABS car drivers harmlessly banged into the backs of cars in the front. Steering away is not always the better option, it could get worse too.

[dadu]

Suman, I agree with you on some part and disagree on the other, since personal experience do form an opinion but personal experiences also differ from person to person and there are human factors involved.

Articles supported with research and statistics form a benchmark for everyone and negate the human factors involved like panicing, oversteering and not applying a firm foot.

Mechanical devices cannot react to human factors and are made to just follow a certain path and do a job.

Fortunately I was able to find such a research by "United States department of Transportation, National Highway Traffic Safety Administration, Vehicle Research and Test Center" and hope it answers all our questions (Its long and I am still reading it).

Light Vehicle Antilock Brake Systems (ABS) Research

Originally Posted by suman

The problem with this thread is that most people (please note bold highlight under most) commenting are being theoretical & will throw various articles & links at you without actually having experienced it in real life.

[comfortfreak]

Originally Posted by androdev

Your professor must be nominated for a Nobel prize! Who was that monkey who invented the wheel and forced on us?

To sir with love,
The wheel can be stopped from rotating by any brake - stone age stuff. The goal is to stop the vehicle and also to keep it steerable. The is where the ABS help.

Correct, but irrelevant. Static friction is for moving something from rest. Our goal is the opposite of it.

Not to argue with gurus but I think the whole point of braking is to kill the momentum of the vehicle with the friction between road and tyre. Static friction is what has to be overcome to move a tyre from rest AS WELL AS to keep the tyre rolling. Ie static friction tries to bring a rolling tyre to stop. Sliding friction tries to bring a sliding tyre to stop. If sliding friction is less than static friction then it is logical that the vehicles momentum can be killed faster by making sure you use only static friction and not sliding friction to stop, thus ABS.

However, I'm stuck with the silly thought that if we had tough rubber that does not burn (some hard plastic type) would you get better FE etc if we had skis instead of rear wheels ????

[androdev]

Originally Posted by comfortfreak

Not to argue with gurus but I think the whole point of braking is to kill the momentum of the vehicle with the friction between road and tyre.

Partially true. It would imply that if you just stop accelerating (without applying the brake), the friction between the tires and the road will stop the vehicle in the shortest distance.

Our intention is to dissipate kinetic energy (kill the momentum) in the form of heat energy generated primarily using two pairs of friction surfaces: between brake pads/discs and tires/road. Maximum friction (and hence maximum heat generation) occurs when brakes are not locked up and tires are rolling.

A sliding tire on road is a more complex phenomena: At high speeds rubber melts and hot gas layers are formed between road and the tire which greatly reduces friction.

However, I'm stuck with the silly thought that if we had tough rubber that does not burn (some hard plastic type) would you get better FE etc if we had skis instead of rear wheels ????

Yes. Don't apply for a patent yet :-) You have to consider traction, comfort, noise, vibration, etc.!

[vasudeva]

Having used an ABS for more than 7 months now, I can say that I am happy that I have ABS. Perhaps the most important benefit is that the car holds a predictable line under sudden stops. At least 2-3 times, whenever I pressed somewhat hard on the brakes to avoid some vehicle in the front right or left making a sudden unexpected deceleration, the instinctive reaction is to lurch back and wait for the car to collide. But now I find my car keeps straight. Overall braking is also more predictable and quicker. I think it is definitely a worthwhile feature and should be preferred over spendings on audio, power windows, etc.

[comfortfreak]

Originally Posted by androdev

Yes. Don't apply for a patent yet :-) You have to consider traction, comfort, noise, vibration, etc.!

Did some googling and realized that there is also rolling friction that is actually less than sliding friction. So I have decided to stick to things I know well and just drive very carefully

[sanchits]

guys...dont forget..ABS comes with EBD...electronic brake force distribution...so you say the breaking distance is increased, i dont agree to this, cause if the ABS decreases pressure on the brakes....the EBD takes care of it, that optimum pressure is applied to all the wheels and reduces the stopping distance. i own a swift zxi and honda civic, and trust me even in normal breaking, the EBD does a great job and really shortens the breaking distance. ABS coupled with EBD also does a great job to regain control on the car after hard braking.
ABS works well only on all wheel disc brakes, therefore in swift zxi, i t doesnt work very well as the rear wheels try to lock up being drums.

[v1p3r]

Originally Posted by anupmathur

In 4WD mode you are very much allowed to turn the steering should you wish to go that way. All part-time 4WD vehicles use limited slip differentials and can handle twists and turns in the path.
The only important condition is that you must use 4WD mode only on surfaces where there is slip and NOT on dry, hard pavement.
If 4WD mode is used on twisty, dry pavement where good grip is available it will lead to rapid wear or even 'binding' of the transmission.

True blue 4WD vehicles offer three differential lock switches which must be engaged as required. Our Gypsy, Scorpio and Safari do not offer this feature.
The Force Motors SUVs are available with this excellent feature.

I don't know about true-blue 4WDs or anything, but all you need is a centre differential to make sure you can run AWD/4WD at all times. Like an Evo or a Forester.

Originally Posted by sanchits

guys...dont forget..ABS comes with EBD...electronic brake force distribution...so you say the breaking distance is increased, i dont agree to this, cause if the ABS decreases pressure on the brakes....the EBD takes care of it, that optimum pressure is applied to all the wheels and reduces the stopping distance. i own a swift zxi and honda civic, and trust me even in normal breaking, the EBD does a great job and really shortens the breaking distance. .

EBD distributes braking power to wheels, according to need. It has nothing to do with increasing pressure that ABS supposedly decreases.

Originally Posted by sanchits

ABS works well only on all wheel disc brakes, therefore in swift zxi, i t doesnt work very well as the rear wheels try to lock up being drums.

I doubt this. What tyres does your Swift have?

[anupmathur]

Originally Posted by sanchits

ABS works well only on all wheel disc brakes, therefore in swift zxi, i t doesnt work very well as the rear wheels try to lock up being drums.

ABS, specially in conjunction with EBD, would prevent any such lock ups. If not, something is malfunctioning and NEEDS to be rectified. Disc/Drum combination should not be the issue here.

[Thad E Ginathom]

Driving today on a good stretch of road (newly laid part of OMR, Chennai) I braked sharply for a pedestrian. There was a screach: ie, the car skidded.

This is not the first time I've noticed this, and I am wondering if this says that the ABS is not functioning?

Car is a Swift VDI, and just coming up to its second service...

[suman]

Originally Posted by Thad E Ginathom

Car is a Swift VDI, and just coming up to its second service...

The Swift VDI has ABS?

[sreenivass]

Originally Posted by Thad E Ginathom

Driving today on a good stretch of road (newly laid part of OMR, Chennai) I braked sharply for a pedestrian. There was a screach: ie, the car skidded.

This is not the first time I've noticed this, and I am wondering if this says that the ABS is not functioning?

Car is a Swift VDI, and just coming up to its second service...

I observed the same in my Mercury a few years ago. There was wheel lockup and slight skid. The speed I was doing would be about 30-35 MPH. There were two possibilities: ABS not functional and the other is it does not really function at low speeds. I would tend to think it is the second one, since the ABS worked pretty well in many other situations.

[Thad E Ginathom]

But 30-35MPH is hardly slow when it comes to having accidents! and wheel lock is wheel lock at 10 or 100MPH.

The only time I have ever experienced ABS working was in my UK Rover 620 (British Honda Accord) when breaking on ice --- at walking speeds. Of course, it didn't help much (nothing can) and I was only playing with it, but the ABS judder in the pedal was unmistakable.

Suman, ABS is optional on the Swift VDI. Seems to be recommended by many of the buyers in the various Swift Diesel threads

[iraghava]

Thad - Try this on an empty road/stretch. Simply stand on the pedal as hard as you can & see if the pedal judders, if not then I guess it's time to ask the Service centre to fix it. Also, on a normal surface the tyres should not lock, check that too.