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Old 6th May 2009, 14:14   #1
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Unhappy Verna ABS Brakes..

All,

I have a Verna CRDi w/ABS Sep 2008 model, clocked abt 11k miles on it so far - without a single problem. My brakes are behaving funny nowadays..
I am able to slam on them in case I need to, and the car stops no problem - whatever may be the speed. But If I brake while on an uneven surface or on a unexpected pothole/speed breaker, the brakes act like they have broken loose from the wheel (gives resistance and I get the feeling that the brakes are struggling to hold on to the wheel and that they are being displaced from their original location). This goes off once I cross the obstacle. The problem (as I call it) may have been there earlier, and I may not have noticed it, but now that I know abt. it, I notice it everytime I have to brake. Braking on normal surfaces is just fine and as it should be.

I am not sure if this is expected behaviour.

Any thoughts / experiences on this one ?
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Old 6th May 2009, 14:49   #2
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Quote:
Originally Posted by amitwadhwa View Post
But If I brake while on an uneven surface or on a unexpected pothole/speed breaker, the brakes act like they have broken loose from the wheel (gives resistance and I get the feeling that the brakes are struggling to hold on to the wheel and that they are being displaced from their original location). This goes off once I cross the obstacle.
This is the ABS at work and doing precisely what its designed do. Hence no need to worry.
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Old 6th May 2009, 14:58   #3
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Amit,

Nothing to be alarmed about. The shudder that you are experiencing is the ABS system at work.

A short technical explanation. When you brake, the amount of pressure you exert on the pedal directly affects the pressure with which the discs retard the driven wheels. The wheel then stops due to friction with the road.

There is a point called the optimum braking point, beyond which any more pressure on the driven wheel will cause the wheel to lose contact with the road, and lock up. Anti-Lock Braking System (ABS) has a sensor which detects whether the optimum braking point has been reached under braking. If more pressure is applied, it automatically releases and applies pressure on the discs, to prevent the wheel from locking up. Thats why you feel the pedal pulsating beneath your feet.

Since on gravelly/uneven surfaces the wheel has a greater tendency to lose grip with the road surface, ABS has to work harder here, even at lower speeds.

OT - For your information, I have a Verna CRDI SX ABS too, and its a Sep 2008 model. I experience the same thing under hard braking.
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Old 6th May 2009, 15:26   #4
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Amit,
I believe that with the ABS you will feel a pumping sensation on the pedals when you hit the brakes hard. This, along with the fact that in a turbo charged engine, if you brake hard, and dont clutch, the turbo charger continues to pull the car forward, causing the entire car to shudder and vibrate like no ones business, are probably a couple of reasons why people find it weird to brake at high speeds. Its probably nothing to worry about, considering that your car is braking perfectly well under normal conditions.
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Old 6th May 2009, 15:30   #5
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And one more piece of info here guys,ABS cars need more stopping distance than normal ones.So whenever we start brakking we would have a calculation as to when this would stop regarding a normal car and we find ABS cars tends to stop only after that distance.So do mark this point in mind to avoid surprises like this .

ram
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Old 6th May 2009, 15:44   #6
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Quote:
Originally Posted by ram_hyundai View Post
And one more piece of info here guys,ABS cars need more stopping distance than normal ones.So whenever we start brakking we would have a calculation as to when this would stop regarding a normal car and we find ABS cars tends to stop only after that distance.So do mark this point in mind to avoid surprises like this .

ram
This is absolutely not correct. ABS, due to its inherent feature of finding the Optimum Braking Point at all times, ensures that the shortest braking distance is achieved.

What you are saying is a myth that has circulated in India for a long time due to incorrect driver habits. When a driver (who's a newbie to ABS) feels the pedal shuddering beneath his feet, he instinctively eases the pressure on the pedal. This reduces the efficiency of the whole braking system and makes the car take more time to stop.

Nothing that cannot be corrected by practice.

Would love to know the source you got this information from.
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Old 6th May 2009, 15:45   #7
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Nice info on ABS, might go for a upgrade to Verna sometime next year.
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Old 6th May 2009, 16:04   #8
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Quote:
Originally Posted by predatorwheelz View Post
When a driver (who's a newbie to ABS) feels the pedal shuddering beneath his feet, he instinctively eases the pressure on the pedal. This reduces the efficiency of the whole braking system and makes the car take more time to stop.
I second this fact, I used to think (and feel) the exact thing above. But I was told by a friend, that you need to be persistent with ABS, ignoring the feedback you get from the pedal. Once I came to terms with that, my car stops dead in its tracks.. I am surprised many a times with the efficiency of the ABS on this car!


Does wear and tear happen on ABS discs too ? (I am guessing it does, its not magic ) What odo reading can I expect before I need a change on my brakes - considering normal riding conditions - and very rare cases where I have to slam on the brakes. ?
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Old 6th May 2009, 16:05   #9
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ABS equipped cars will have a longer stopping distance on loose surfaces like gravel or snow. This is because for any sort of traction during hard braking, the tires need to dig in - ABS doesn't let your car do that. In all other circumstances, ABS will let you stop better and avoid obstacles while doing so. It is my opinion that the fact that ABS lets you steer while providing optimum braking is it's biggest advantage.

Wear and tear is no different in ABS equipped cars.
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Old 6th May 2009, 16:09   #10
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Quote:
Originally Posted by ram_hyundai View Post
And one more piece of info here guys,ABS cars need more stopping distance than normal ones.So whenever we start brakking we would have a calculation as to when this would stop regarding a normal car and we find ABS cars tends to stop only after that distance.So do mark this point in mind to avoid surprises like this .

ram
Quote:
Originally Posted by predatorwheelz View Post
This is absolutely not correct. ABS, due to its inherent feature of finding the Optimum Braking Point at all times, ensures that the shortest braking distance is achieved.

Both of you are partly right IMHO , on normal roads the ABS takes lesser distance if braking is done properly, where in special conditions like wet roads, sand/ gravel on road or ice/snow the abs would take more distance to stop. But do note that the primarly objective of the ABS controller is to ensure that the tyres do not skid , so that the driver is always in control of the vehicle.
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Old 6th May 2009, 16:09   #11
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and thanks a lot to all of you, that was some serious techie stuff on ABS. I tried doing reading up on ABS, but bookish articles can barely match experience of Team BHP folks. Its a relief to know that I dont already have a technical problem in my car after just 11k kms.
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Old 10th May 2009, 22:44   #12
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Quote:
Originally Posted by predatorwheelz View Post
This is absolutely not correct. ABS, due to its inherent feature of finding the Optimum Braking Point at all times, ensures that the shortest braking distance is achieved.

What you are saying is a myth that has circulated in India for a long time due to incorrect driver habits. When a driver (who's a newbie to ABS) feels the pedal shuddering beneath his feet, he instinctively eases the pressure on the pedal. This reduces the efficiency of the whole braking system and makes the car take more time to stop.

Nothing that cannot be corrected by practice.

Would love to know the source you got this information from.
Unfortunately, PredatorWheelz, I believe you are the one labouring under a misconception.

Please read the section on this page: Car Bibles : The Brake Bible that deals with ABS.

It's a really fantastic site. Warning-- can be addictive the first time you visit it

To quote a paragraph from the page:

Quote:
So how to talk about the biggest misconception about ABS - that it will make you come to a stop more quickly? This is a prickly subject to talk about. In one camp you have drivers like me who just can't stomach the idea of a computer breaking the physical connection between my right foot and the brake system. Whilst in the other camp you have people who believe that ABS is the best thing since sliced bread. It's these people in the second camp who have the all-out belief that ABS will help you stop faster, and in certain conditions, this is true. On a wet or greasy road surface where the traction is severely reduced, an ABS system can pulse the brakes and prevent lockup much better than a human can.

But why? The whole point of brakes is to slow you down. To do that they rely on friction in two places - between the brake pads and the rotors, and between the tyres and road surface. If one of those factors is taken out of the equation, the brakes become useless. The most typical situation is that a driver will panic-react to something and step on the brakes with as much power as they can muster. The brake system amplifies this power, grabs hold of the brake rotors and the wheels stop turning almost instantly. This causes the tyres to now skid across the road surface, and as they do so, they become subject to dynamic attrition. In other words, if a tyre is rotating and gripping the road, the "stick" factor is much higher than if the wheel is locked and skating across the same surface.

So that's what ABS does - in an emergency, it ensures that the wheels don't lock up but instead keep spinning so that the tyres maintain grip with the road. (That's where ABS gets its name - Anti-Lock Brakes.) This is where the real benefit of ABS comes into play. If you're going to attempt to avoid an accident, the best thing to do is to try to steer around it. If your tyres are skidding on the road surface, you can point your wheels pretty much wherever you want because the actual direction you end up going will have nothing to do with the wheels and everything to do with the direction you were travelling, combined with the camber of the road. Once the tyres lose grip, all bets are off. With ABS, if those wheels keep turning and the tyres keep gripping, then when you ham-fistedly grab the steering and yank it to one side, the car will still turn and you might be able to avoid the accident. So that's the true essence of ABS - to maintain control over the direction of the car.
(Paragraph split into three for easier reading in forum format.)

Last edited by Perakath : 10th May 2009 at 22:48.
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Old 10th May 2009, 23:06   #13
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Perakath,

The original argument was about Ram's claim that ABS cars need more stopping distance than normal ones. Where does it say in the paragraph that ABS needs more stopping distance? In fact, if anything, it enhances my statement that ABS does not let the wheels lock up in an emergency and keeps the wheels spinning.

And just a request boss. Please dont use such strong statements like I'm labouring under a misconception, unless you have arguments strong enough to prove me wrong.
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Old 10th May 2009, 23:18   #14
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Quote:
Originally Posted by predatorwheelz View Post
The original argument was about Ram's claim that ABS cars need more stopping distance than normal ones. Where does it say in the paragraph that ABS needs more stopping distance? In fact, if anything, it enhances my statement that ABS does not let the wheels lock up in an emergency and keeps the wheels spinning.

And just a request boss. Please dont use such strong statements like I'm labouring under a misconception, unless you have arguments strong enough to prove me wrong.
Here's the very next paragraph from the site:

Quote:
My bone of contention with ABS is not so much to do with the technology as the placebo effect is has on drivers. ABS is widely misunderstood and if you ask most drivers, they'll tell you that ABS helps them to stop more quickly, and as I illustrated above, in certain conditions this is true. But even the most well-trained driver is going to be subject to panic in an emergency, and more often than not, will lock their arms on the steering wheel bracing for the coming impact. Once you do this, you're no longer steering so the ABS is trying to give you control over your car but you're not taking advantage of it. Given that this is the most natural human instinct, people accept this as "the way of crashes" but somehow believe that if they have ABS, they'll be able to stop before they get to the point of impact, and that's simply not true. I believe too many people think ABS gives them a license to drive faster, because they mistakenly believe that it will get them out of any situation.
I agree completely with the views expressed by the author of the paragraphs I've quoted. You may not, and the author says as much in his writing. However, I notice you've not provided any proof to substantiate your rather forceful claims, whereas I have clearly displayed the basis on which I've formed the views I hold.

I'm not saying ABS always = larger stopping distances. I'm just trying to point out that until I read the article I've linked to, I too was under the impression that ABS somehow made the brakes more powerful. Perhaps others have the same misconception. Of course, we both agree that when the car is in a skid and the wheels are sliding instead of rolling, there's very little braking happening for the duration of such slide. When ABS prevents such a skid, it may indeed allow a faster stop.

"Labouring under a misconception" is a relatively common idiom in English. No offense meant to you personally, of course.

Last edited by Perakath : 10th May 2009 at 23:37.
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Old 10th May 2009, 23:28   #15
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Quote:
Originally Posted by predatorwheelz View Post
Since on gravelly/uneven surfaces the wheel has a greater tendency to lose grip with the road surface, ABS has to work harder here, even at lower speeds.
Quote:
Originally Posted by ram_hyundai View Post
And one more piece of info here guys,ABS cars need more stopping distance than normal ones.
I feel there is only partial understanding here of what we should expect from ABS.

On hard tarmac or concrete, ABS stops faster. It prevents lockup on any single wheel through separate channels, and utilises the maximum coefficient of friction from each tyre with the road. You can release & reapply pressure on non-ABS brakes, but then you're reducing pressure on all wheels, so braking efficiency reduces.

When you've got the two wheels of one side on gravel, or there's a patch of oil or sand on the road, ABS still wins. Non-ABS brakes applied hard here can spin the car due to the difference between left and right sides - one side skids and outruns the other, so you spin.

It's only when all 4 wheels are on sand or gravel, or even snow, that ABS loses out. The computer controlling the system goes haywire. Here, each wheel locks up a few milliseconds before the other, and ABS is doing overtime in trying to keep any of them from locking up. And fails miserably. But the non-ABS system locks the wheels, and allows them to "dig in", piling up sand or gravel in front of its path. Stops the car faster. And this is also what cadence braking is about.

On oil or ice, ABS or no ABS, you're on your own. Just check your car insurance is valid.

Last edited by SS-Traveller : 10th May 2009 at 23:30.
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