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> From quattro-owner@swiss.ans.net Fri Dec  9 04:29:58 1994
> Date: Fri, 09 Dec 1994 07:38:26 GMT
> From: Phil@sievers.demon.co.uk (Phil Payne)
> To: quattro@swiss.ans.net
> Subject: Re: ABS
> Lines: 37
> Reply-To: quattro@swiss.ans.net
> In message <941208223749_1064996@aol.com> OREO447766@aol.com writes:
> >>       "ABS will, of course, almost always LENGTHEN your braking
> >>        distance.  Does anyone 
> >>        here ever switch it off - and if so, why?"
> >     Phil, I'm concerned about the above statement. This may need some
> > clarification. ABS' pulsing action to modulate pressure will almost always
> > reduce braking distances, it also has the added advantage of allowing the
> > driver to concentrate on steering.
> >      Disclaimer: None of my rigs are ABS equipped, so these words are based
> > on textbook knowledge, not road tests. 
> This is now my eighth year driving mainly ABS-equipped vehicles.  Four 
> separate Ford Granadas and a ur-quattro.  My experience with the Granadas was 
> that ABS lengthened braking distances by 10% to 30%, but increased steerability 
> and predictability.  I've verified this with the ur-quattro, where you can 
> actually disable the ABS.
> I also had the benefit of Audi's thoughts during a session at the Weissach test 
> track, when "Project Tetra" was being developed (1982/3).  This was later 
> released as the "syncro".  The team there said that the shortest braking 
> distances were achieved without ABS, and the Audi "quattro driving course" (two 
> days free for early 80Q buyers) taught drivers to make a downward sweeping 
> movement with their right hand. The idea was to hold the index and middle 
> fingers a little way apart and pull out both differential locks in one 
> movement.  They were also VERY strong on the "brake early and hard" principle.

One problem with the above data: it's TWELVE YEARS OLD.  The statements
that a good driver can outperform and ABS system pertain to
slow-pulsing, first-generation ABS systems.  From Bosch ABS IV on, this
is no longer true; the speed of each wheel is adjusted far more
accurately and at 25 millisecond intervals (audio frequency--40 Hz.).
On surfaces with varying frictional coefficients (patches of water,
ice, oil, leaves, sand, or even small bumps) results are no less than
stunning--far shorter than what a human could ever hope to acheive.

A human actuating a single brake pedal cannot possibly adjust the braking
on four separate wheels forty times per second!  However, the best
old systems managed only 10 per second, and even some new ones--like
in Saturns--pulse only a few times per second.  A human can easily
outperform the low-budget Saturn system.  No one would ever lump
the performance of an 8086 with that of a Pentium, and the same
should not be done with these systems over the same time period.

Tyre compounds have also changed to take advantage of ABS.  At one time, 
braking distances were tested with locked wheels, and compounds optimised
for such.  Now all testing of high-performance tyres is done with ABS-
equipped vehicles, and the tyre designed for best performance under these
conditions.  Thanks to everything working as a system, new records in
short braking distance are being set every year.

John Greenstreet, Senior Engineer           (jgreenst@motown.ge.com)
Martin Marietta Government Electronic Systems    Moorestown NJ 08057
WPI Class of '75, Temple Class of '94

My new car history:
  1975    1978    1982       1986        1989      1992      1995
   VW ->  Audi -> Audi  -> Mercedes -> Mercedes -> Audi -> Mercedes
Scirocco Fox GTI  4000S    190E 2.3    190E 2.6    100CS     S320

POSSLQ's* new car history:
         1978       1981       1985      1988        1990     1993
       Triumph ->  Toyota ->  Toyota  ->  VW    ->   Audi  -> Audi
       Spitfire    Tercel     Corolla   Jetta GL      80      90S

*POSSLQ = Person of Opposite Sex Sharing Living Quarters
Note: All Audis and Mercedes above were sold to friends or family.