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was Speeding in the UK now ABS

To: cdsorkin@ix.netcom.com, mgs@autox.team.net
Subject: was Speeding in the UK now ABS
From: REwald9535@aol.com
Date: Sun, 9 Jan 2000 00:09:11 EST
In a message dated 01/08/2000 6:48:33 PM Pacific Standard Time, 
cdsorkin@ix.netcom.com writes:

> Unrelated question about ABS systems:  On normal dry road surfaces, with
>  properly functioning brakes, doesn't an antilock braking system cause the
>  car to require a LONGER stopping distance?
>  


Decreased stopping distance is not design function of ABS.  What ABS is 
designed to do is to prevent the wheels from locking (this is why they call 
it ABS not shorter stopping thingy:-)  The second design criteria is that the 
system work at all speeds and going around corners as well as in a straight 
line. (it does disconnect at a couple of MPH where it is immaterial) Lastly 
the system must be automatic and not require any special driver intervention.
Stopping distance is a function of traction of the tire against the road 
surface.  As you step on the brake the tire starts to slip on the road 
surface (slip is fairly constant, for instance when going 60 mph on a dry 
flat road your drive wheels are going about 61 to overcome drag)  As slip 
increases stopping force increases, and stopping distance decreases.  To a 
point.  When slip exceeds about 15% braking force starts to decrease this is 
commonly called a skid.  The further slip goes above the 15% the longer the 
stopping distance becomes. The greatest stopping force is generated just 
before the tires start to skid (keeping the wheel slip in the 12-15% range)  
Now can a non-ABS car out stop an ABS car?
Well, that depends on a couple of factors, first would be the car's ABS 
system.  Volvo (the guys that pay my salary) make a brake system that will 
stop on a dime and give change.  I have driven rental cars, on the other 
hand, that when put into ABS (a guy cut me off) made me think that I could 
drag my feet and do better.  The second item is just how good is the driver 
of the non-ABS car?  I know that everyone thinks that they are superb 
drivers, and in truth this list's drivers are, I'm sure, better than most, 
but, and this is a big but, I have to ask this question.  When presented with 
an emergency can you absoulty and positively guarantee that you can brake the 
car to the 12-15% slip range and modulate the brake and hold it there without 
going above 15% slip and going into a skid?  I know race drivers can, in a 
race, but can you when presented with an idiot who pulls a U-turn directly in 
front of you (like a melon head did to me tonight)
One more point a race driver can modulate a brake pedal about 5-6 times a 
second, pretty good huh?  A modern ABS system can modulate each of 4 wheels 
indepently up to 15 times a second.
So in answer to your question I would say that most of the time (99.9%) given 
a good ABS system, the ABS car will out stop a non-ABS car.  This answer 
applies to pavement only (dry or wet) snow, gravel, and sand ABS will give a 
longer stopping distance.  The only advantage of ABS in snow, gravel, or sand 
is control. To get the shortest stopping distance in snow you must lock the 
brakes and build a pile of snow in front of each wheel.  However when the 
wheels are locked you have no steering control.  ABS may take longer to stop, 
but you maintain control.
Now for a trivia question what does ABS stand for?
Sorry for being so long winded, hope this explains a little,
Rick Ewald


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