Re: Chirps

["Graydon D. Stuckey" <graydon@apollo.gmi.edu>]

On Fri, 14 Jun 1996, Al Powell wrote:

> My experience is that if you really nail the ABS, you do get 
> intermittent "chirps from the tires as they NEAR lock-up before 
> releasing, so I would expect that you might see some small black 
> marks here and there through the braking path, as it's possible that 
> the tires would leave a small mark as they "chirp".  No black LINES, 
> though.  A solid line would indicate lock-up
Yep,

	I have seen lots of pictures of ABS-equipped skid marks, and they 
aften leave dotted lines, instead of the customary solid lines.  Therein 
lies the secret to why most topend race cars don't use ABS.  That space 
between the dark lines indicates that there was a discrete amount of 
time in which the brakes were not braking at their ultimate capability.  
The dark line, if the ABS system is calibrated well, indicates thath teh 
tire was exceeding the 4-5% slip that is optimum (Not sure about the 
number, but I think it should be around 5%.)  If you were to add the time 
spent just a little over the optimum braking point, and the time spent 
well below the optimum brakign point, you would find that the total 
braking experience was less effective than a well modulated manual brake 
system with a sensitive foot on the pedal.  IN this case, you would see a 
light steady gray line along the entire distance.

Later,								
Graydon D. Stuckey								
graydon@apollo.gmi.edu								
Flint, Michigan   USA
'86 Audi 5000 CS Turbo Quattro, GDS Racing Stage II