The ABS discussion thread

[sudarshansarma]

It is often debatable that ABS will shorten stopping distances when there is sand/debris. However that is inconclusive. It depends on various things like suspension, tyres etc...what it does is to help you steer the car under emergency braking. You cant retrofit ABS as it is a module controlled by its own ECM and has various sensors which can be fit properly only at the time of assembly...according to me it should be made compulsory by law!

[dadu]

No its not, the test agencies do the various tests under varied conditions and have published their results, the only thing debatable will be on how the person will respond under such conditions and use his/her mind to use the ABS and vehicle control.

Originally Posted by sudarshansarma

It is often debatable that ABS will shorten stopping distances when there is sand/debris.

[comfortfreak]

FWIW, I have really experienced a serious case of locked wheels only once. While testing out a newly bought car I took an exit from highway at double the proper speed, realized too late the curve was steeper than I expected, braked hard and the next moment I was like on a snow board gliding smoothly with little resistance over the road surface towards the edge of the bend. This was a car without ABS and my instincts did not make be pump the brake either. However, lucky for me, I instinctively turned the steering sharply to the opposite direction which now made the car slide to the other side. I had to do this back and forth a 2-3 times (in the space of a few seconds) and then the car slowed enough to control again. The whole procedure felt exactly like how they teach you to control the vehicle when it starts sliding on snow.

I have never had the chance to fully experience a panic stop on a ABS, but without it I can vouch that once tyres start sliding car WON'T stop easily - irrespective of the friction between rubber and road.

[mithun]

Originally Posted by 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.

Are you saying that ABS will surely help in roads with intermittent sand/pebbles/loose tarmacs that's prevalent in India ?

[suman]

Originally Posted by mithun

Are you saying that ABS will surely help in roads with intermittent sand/pebbles/loose tarmacs that's prevalent in India ?

Actually you guys are amazing! Tell me, how much of your actual driving is on non-tarmac? As a percentage of your total driving?

Judging by most of your comments, you seem to be looking for a scenario where ABS may not be most effective & keep harping on that.

Do you think you'd be doing more than 5 to 7% of your total driving life on snow or gravel or pebbles? I would think not. Yet you go on & on & on about how ABS is ineffective in these kind of conditions. And ignore the fact that 93 to 95% of the time, you would be on tarmac & wet roads & expressways where ABS would be a life saver. Period

[1100D]

Originally Posted by mithun

Are you saying that ABS will surely help in roads with intermittent sand/pebbles/loose tarmacs that's prevalent in India ?

It will surely help one in maintaining composure of the car and steer in a specific direction, however the braking didtance will be longer on roads defined by "roads with intermittent sand/pebbles/loose tarmacs that's prevalent in India".

So it helps on one and hinders on the other, so its upto one's judgement which one he will choose.

[anupmathur]

Originally Posted by Samurai

But when you are in 4x4 mode (I don't mean AWD), you are not supposed to turn the steering.

ABS is useful in good roads at higher speeds, while 4x4 mode is used off road at crawling speeds.

Sorry, Samurai. Your information is incorrect.

[skidrock]

According our Physics professor, sliding tyres travel longer before coming to a stop than rolling tyre does.
When you try to stop a rolling wheel without sliding it, it need to overcome the static friction, unlike the sliding wheel which need to overcome sliding friction.

Now coefficient of static friction is more than coefficient of sliding friction for a given pair of materials.

That way even on dry tarmac roads, even on straight line, ABS equipped car stops quicker than a non-ABS car does.

I believe that ABS not only helps to steer in panicked braking conditions but also decreases the braking distances in straight line braking too. And that's why ABS is a must. Period.

[mithun]

Originally Posted by suman

Actually you guys are amazing! Tell me, how much of your actual driving is on non-tarmac? As a percentage of your total driving?

Judging by most of your comments, you seem to be looking for a scenario where ABS may not be most effective & keep harping on that.

Do you think you'd be doing more than 5 to 7% of your total driving life on snow or gravel or pebbles? I would think not. Yet you go on & on & on about how ABS is ineffective in these kind of conditions. And ignore the fact that 93 to 95% of the time, you would be on tarmac & wet roads & expressways where ABS would be a life saver. Period

I've to drive about 3 KMS daily through a rubber plantation filled with loose pebbles before even entering the main tarred road !

That's why I've raised this question !

[Samurai]

Originally Posted by anupmathur

Sorry, Samurai. Your information is incorrect.

I'd appreciate some supporting information.

[suman]

Originally Posted by mithun

I've to drive about 3 KMS daily through a rubber plantation filled with loose pebbles before even entering the main tarred road !

That's why I've raised this question !

Mithun, the question is not only to you but to all who have kept on harping about ineffectiveness of ABS on gravel. My question is - what percentage of the total driving is on this kind of road?

[GSHA]

Well... So much has been discussed on the ABS... Here goes my experience in braking!!!

1997: Car: Toyota Tercel (the size of our Esteem). Place: US of A. On a curved exit ramp that had sheet ice, I touched the brakes to stop for the lights... The car went spinning!!! It did a 270 and stopped, luckily, on the side of the road without hitting the barricade / sidewalls. Of course, the Tercel did not have an ABS.

2001 to 2006: Cars: Alto and Baleno. Several instances of having to brake hard on the highways / loose gravel side roads in deep Tamilnadu. On gravel / loose surface, one or more wheels always lock up under sudden braking and there were always a skid / loss of control.

2007: Cedia. Has ABS. My only car so far with ABS!!

Given that I drive on the country roads sometimes (less than 5% of my distance covered, though), I have had donkeys / cows / humans jump in from sides of the road, after losing their senses. These roads are narrow (single tracks), paved at places, big potholes, loose surface at stretches. With the ABS, the behavior during heavy braking is totally different.

1. The wheels don't lock up - no screeching.
2. The steering works. Without the ABS, when the wheels locked up, the direction of motion is disconnected from the steering!!
3. The vehicle "feels" as if no brakes have been applied - this is a perception issue I had, because of lack of any tire screeching. But, comes to a quick stop, nevertheless.

As for stopping distances, I haven't measured them. But, whenever I felt the ABS kick in (the pumping noise from the brakes), I felt that the vehicle came to stop with less drama!!

Definitely Confidence inspiring!!

[suman]

Thanks GSHA - its good to hear from someone who has actually experienced both ABS & non-ABS cars. Being another one who has, I always find it more confidence inspiring - I have many a scary recollection of wheel lockups & near misses in my earlier non-ABS vehicle experiences (and a couple of hits as well!)

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!

[androdev]

Originally Posted by skidrock

According our Physics professor, sliding tyres travel longer before coming to a stop than rolling tyre does.

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

When you try to stop a rolling wheel without sliding it, it need to overcome the static friction, unlike the sliding wheel which need to overcome sliding friction.

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.

Now coefficient of static friction is more than coefficient of sliding friction for a given pair of materials.

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

[anupmathur]

Originally Posted by Samurai

I'd appreciate some supporting information.

Originally Posted by Samurai

Now this is a good example of an oxymoron. The main advantage of ABS is that it allows you to turn while braking. But when you are in 4x4 mode (I don't mean AWD), you are not supposed to turn the steering.

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.

Originally Posted by Samurai

.. while 4x4 mode is used off road at crawling speeds.

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.