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Old 24th January 2009, 23:44   #1
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Default ABS takes longer distance to stop?

Although ABS is good to prevent wheel-locks and skids but some say ABS takes longer distance to stop than a non-ABS car. Is it true? Experts, please throw some light on this as it will immensely help people choose between shorter braking distances and no wheel lock-ups. They say you can't have both.

Last edited by pgsagar : 24th January 2009 at 23:49.
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Old 25th January 2009, 00:45   #2
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Yes. I've seen this on T-Bhp before as well.

and

A June 1999 National Highway Traffic Safety Administration (NHTSA) study found that ABS increased stopping distances on loose gravel by an average of 22 percent.
(Source : Anti-lock braking system - Wikipedia, the free encyclopedia)
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Old 25th January 2009, 04:16   #3
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Quote:
Originally Posted by pgsagar View Post
Although ABS is good to prevent wheel-locks and skids but some say ABS takes longer distance to stop than a non-ABS car. Is it true? Experts, please throw some light on this as it will immensely help people choose between shorter braking distances and no wheel lock-ups. They say you can't have both.
My dear man...ABS allows you steering control of the car during emergency & panic stops...something which a locked tyre can NEVER do.

Also, to actually stop shorter distances than ABS one needs to PRACTICE panic stops on the regular basis to get to know the cars behaviour at the limit. By this i mean that one has to feel impending wheel lockup & then release the brakes & repeat the process...all this while steering the car & keeping your eyes on the road!

So, ABS does it all for you. Also, do tell me how many drivers on our public roads actually have the time, energy or even inclination to practice panic stops on a regular basis?

ABS is the best thing to happen to cars since the internal combustion engine!
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Old 25th January 2009, 05:05   #4
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^Aye capn' Haddock !

right, ABS regulates the pressure at the brake pads and when it senses that the one(or more) of the wheels is about to lock. One can certainly put great tyres and probably even fit aftermarket brake pads for better braking power. But that does not stop the sand, small gravel or any other traction-reducing element to essentially bring the frictional coefficient between the road and the tyres down considerably.

So when you slam on the brakes the brakes do work great. The wheel locks due to the braking power given by the brake pad's force on the disk to retard the wheel's movement down significantly. Therefore the wheels tend to slow down abruptly. Now the inertia of the car tends to not allow any change in the state of the car. So the tyres bear the brunt. When the inertial force & braking power is greater than the frictional force between the tyres and the road, the wheel locks.

Now when the wheel locks the rubber melts which further reduces the frictional force. So if you do lock up for a good amount of road length (i.e skid ) , even if you release the brakes you may not be able to get back the control of the car because the tyres have melted which may throw the car in a spin.

ABS + EBD is the ideal package since EBD can actually distribute the braking force separately as per the need. Suppose you are half on tarmac and half on the road, the ABS would reduce the braking pressure on all the wheels. Rendering it ineffective since the ones on the road would have braked better but now cannot. But EBD can regulate with the ABS so that the wheels on the sand will receive lesser pressure than the ones on the road.

ABS + EBD it'd be for me.
and no matter how much you practice, something or the other is out there to make you panic.

Last edited by Xeno : 25th January 2009 at 05:22. Reason: spell check, punctuation edits. : P
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Old 25th January 2009, 05:54   #5
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Read the wiki article in the link given by Abhinav.

Quote:
While ABS offers improved vehicle control in some circumstances, it can also present disadvantages including increased braking distance on slippery surfaces such as ice, packed snow, gravel, steel plates and bridges,
Although I think I'll disagree with this fact. ABS here in these situations would actually prevent the wheel from locking at all. If you slam the brakes on a iced expressway (common in USA and European countries) your brakes will lock and you'd skid. One wouldn't be able to regain control in such a situation.

The ABS would reduce the braking power in such conditions quite significantly since that braking power will not be useful in such conditions.

OT

Quote:
Risk compensation

Anti-lock brakes are the subject of some experiments centred around risk compensation theory, which asserts that drivers adapt to the safety benefit of ABS by driving more aggressively. In a Munich study, half a fleet of taxicabs were equipped with anti-lock brakes, while the other half had conventional brake systems. The crash rate was substantially the same for both types of cab, and Wilde concludes this was due to drivers of ABS-equipped cabs taking more risks, assuming that ABS would take care of them, while the non-ABS drivers drove more carefully since ABS would not be there to help in case of a dangerous situation. A similar study was carried out in Oslo, with similar results.
well that what we humans do eventually when we have better technology. *sigh*
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Old 25th January 2009, 14:54   #6
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No need to start this discussion here, pls read this (The ABS discussion thread)
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