[200q20v] Re: [s-cars] upgrade advice

Linus Toy linust at mindspring.com
Wed Nov 28 00:53:36 EST 2001

At 08:39 PM 11/27/2001 -0500, Kirby Smith wrote:
>I fail to see a direct relationship between acceleration and
>deceleration in street use.  One accelerates to the speed he can manage
>or with which he otherwise avoids trolling for tickets.  This speed
>occurs sooner with more HP, but likely occurs anyway with lesser HP.
>The need to brake well is always there, and the requirement is
>independent of HP in most cases.  In my opinion, the goal should be for
>pads that are capable of locking up the tires one chooses to use.  More
>braking than that is not needed.  Heat soak resistance is useful, and
>that is the greatest advantage of high performance brakes.  But unless
>one generally rides his brakes down Pikes Peak, or equivalent, in street
>conditions heat soak is an unlikely occurance.  Otherwise, one is likely
>driving without sufficient margin to avoid death-defying surprises.
>Little of the above applies to track use.


*  Audi appears to have a certain philosophy when it comes to designing
brake rotors.  they appear to be real good for one stop, then boom--heat
soak, because they don't have good ability to reject the heat
afterwards.  couple reasons here.  look at the size of the vent veins--the
air gap in the middle.  the metal on the sides of the Audi rotors I've seen
(stock '91 200q w/ G60, '92 100s w/ Ate 1 piston and A8 rotors) is very
thick, leaving only a small air gap.  now compare that with the veins on a
993tt rotor (as in the Movit kit).  relatively, the sides there are much
thinner, leaving a much larger vein.  true, the 993tt rotor is 32mm thick
vs. 25mm for the rotors I noted above.  second (perhaps bigger)
problem:  for the above Audi rotors, the rotor vent intakes are on the
outboard side of the rotor--that is, facing the wheel.  not the place to
get cool air to the rotor (air flow tends to go from this area to the
outside of the wheel).  even ducting to the hub carrier will not help get
enough air into the brake veins--you'll only manage to cool the inboard
surface of the rotor.  BMW did a similar thing on one of their cars, but
there, they have an easy solution with a bigger car's rotors, where the
vent intakes are on the inboard side of the rotor.

*  with more HP, you can get back up to speed sooner than with less...and
encounter another heavy braking opportunity that much sooner.  remember the
cooling issue above

*  sizing brakes to give you only enough ability to lock up your chosen
tires gives you no extra capacity, and no margin for error.  which leads to...

*  arguably, this is less relevant on the street (vs track).  but there's a
lot of distraction on the street.  to paraphrase Brett's response, brains
can fade as fast as--perhaps faster than--brakes.  it's easier (and
cheaper) to accommodate for brake fade than brain fade.  Brett's
right:  chips don't belong on a G60 equipped 20v.  this was me for
awhile.  that was a mistake.  fortunately, I escaped with no incidents
during that time.

*  tracking your car, at least once, IMHO, is a good thing--you get to
learn your limits in your car.  do you really know what you can do with
your car when faced with an adverse situation?

*  BTW, your Pikes Peak scenario:  too realistic.  incident some years back
involving a Chrysler minivan coming down Mt. Constitution (Orcas Island,
Washington state).  boiled the brake fluid, van ran into a campground,
serious injures resulted.  owner never changed brake fluid (not specified
in owners manual).

*  Linus Toy                      Insanity is doing the same thing   *
*  Mercer Island, WA              you've always done and expecting   *
*  linust at mindspring.com          different results                  *
*                                      - Roger Milliken              *

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