Re: ABS

[alex.fadeev@xxxxxxxxxxx]

Michael <mike5635@domain.elided> wrote:
> 
> When I took the Skip Barber school back in 1986 (in a
> 1986 535i), they had us do panic stops with the ABS
> turned on.  Then, they turned it off (had modified
> cars with ABS switches) and taught us to use
> "threshold braking" techniques.  If a skid (and ABS)
> occurs at a 10 out of 10 brake pressure, the maximum
> threshold braking is 9.9 pressure.
> 
> Funny thing...once we learned threshold braking, we
> stopped significantly quicker and shorter distance
> with Threshold Braking than with ABS.  The instructor
> said (if I remember correctly) that ABS is only
> preferred when on snow-covered ice or something like
> that. 

Michael,
Correlation does not imply causation. Just because Skip Barber single 
seaters had lousy ABS computers does not mean all ABS systems are inverior 
to threshold braking.
Things are a lot more complicated that you may be assuming.
For starters, there is a myriad of ABS systems out there. Some work better 
than others. Detroit 2-channel ABS systems are notoriously lousy. 
3-channel are better. BMW 4-channel brakes are above average. Porsche's 
and high end MB's are among the best. Most club racers I now run with ABS 
enable on later (E36 and E46) but frequently prefer to threshold brake 
themselves with old ABS cars (2002 and E30s).

And than there is the issue of independent brake application to each one 
of the four wheels. Well calibrated 4-channel ABS system allows threshold 
breaking at _each_ of the four wheels. Good luck trying that with one 
brake pedal!

Afterall, if ABS did not provide a competitive advantage, F1 would not 
have ruled it illegal.

> Personally, if I trigger the ABS, I feel that I've screwed up!

There are in fact times when my E36 ABS trigger prematurely. One 
repeatable situation is when I hit a minor bump or a pot hole under 
braking. Very annoying, but still more consistent and cheaper than flat 
spotting a tire or going off in the rain without ABS.
And than there are times when locking the wheels offers shorter stopping 
distances due to the nature of road surface.
On the balance, ABS is a very good thing. Too bad that most people, 
include the earlier mentioned cops, don't know how to use ABS. The most 
common mistake is easing or keeping constant the brake pressure when ABS 
kicks in. Almost as bad as throwing your hands up in the air and closing 
your eyes.

alex f

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