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ABS Mysterys, was: ABS and "straightening"

To: Rick Brown <rbrown7@covad.net>, ba-autox@autox.team.net
Subject: ABS Mysterys, was: ABS and "straightening"
From: "Donald R McKenna" <donbarbmckenna@earthlink.net>
Date: Sun, 18 May 2003 03:25:58 -0700
Rick Brown writes:

>Also, many ABS systems have lateral accelerometers which more aggressively
>reduce rear brake effort when cornering.  This helps keep the car from
>swapping ends if you stomp the brakes in a corner but also makes the car
>difficult to point in using  trailing braking.

Some C4 Corvettes, at least '96s,  have a lateral acceleration sensing mode
that, under some circumstances, causes the brakes to go into "ice mode". The
system thinks, because of quick-sequence R then L or L then R transitions,
that the car is on an "ice-like surface" and is tail-wagging into a spin.
When this happens just as hard braking is attempted (like at the end of the
Tour's Saturday second slalom) the brake pedal feels like there's a brick
under it and no matter how hard you push the brake's slowing effect is
minimal. In my experience, I think more than rear braking (Rick's comment)
is effected as the car really won't stop. In this mode there is no normal
ABS pedal "pulsing" feed-back, just that "brick" feeling.

One has to learn a different defensive technique to avoid this problem from
"running" you off the course. Unlike the conventional wisdom ABS reaction of
not pumping the brakes when ABS has been activated (a quick pump engages the
dreaded "ice mode" on mine), you have to anticipate the quick-transitional
moves and either lift/slow earlier or brake just slightly later after the
multiple transitions. Like really late braking! 

Working on mastering this technique.

An alternate solution in SP classes is to experiment with dis-abling the ABS
and then re-learning how to NOT lock the brakes.

        Don

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