[s-cars] apparently warped rotors, when hot

[QSHIPQ at aol.com]

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One of the best brake tools you can own is an IR temp gun (even the one off
the snap on truck is only 125USD).  What you find is that you can get brake
education walking around any qclub paddock, btdt many times.  The sites
referenced by Keith are good, and I've always advocated that if you have a brake
problem with stock pads, you'll have one with more agressive pads...  The problem
with S cars as I see it, is massive weight transfer under hard braking creating
a heat problem.  Just obstructed design wheels can vary temps on the same car
by over 50f, btmt.  The bigger problem is audis lack of attention to good duct
work of fresh air to brakes.  The old v8 is about the only one where audi
mimicked BMW with fresh air attention to the rotors thru the frame rails.  But
all is not lost, the best trick I saw was our own Brendan Rudack laddy.

Brendan's method was to buy 3in ducting, a couple of zip ties, and install
temporary ducting to his brakes when doing track events.  After the event, he'd
get under his (ex)1.8t, hook up the exhaust and snip the ducting and throw
them in the trunk.

POR, I use caliper temps, not surface temps for a couple reasons.  IR temp
senders don't take reflective metal very accurately, and specific to my case, my
temp range maxes at 7500f.  IME, Big reds and the stock textars are good to
about 400f, at which point they can run for a long time at this temp.  Above
this temp, interesting things happen.  First, pretty consistent readings in the
350-400 range are usually found on both calipers.  When you "hit" 400f, the
temp readings tend to jump wildly side to side, and increase exponentially.
This indicates to me that the pad/rotor heat is at "max", and anything beyond, is
destructive mode.  This was also verified on a set of big reds attached to a
couple of porsches as well.

My experience (YMMV) is that targetting 350f in caliper heat with a max of
400f will allow you to run whatever you want using stock textars as the
baseline.  I'm not a big fan of  more agressive aftermarket pads, usually because they
tend to work at the expense of expensive big red rotors.  IMO a better
program is to address the heat, and do it with prejudice, ie, however you can.  If
it doesn't look pretty, who cares, it's 2 days on the track....

WRT pad recommendations, I've always been a stock pad guy.  That said, for a
couple of the race minded folks, I've acquiesed somewhat and will go to the
Pagid Oranges, with little sacrifice in driveability.  A couple cars use oranges
for track, then back to textars to go home, a really good way to keep you off
the couch for the week following the event (read: squealing miss piggy).  Any
more than the oranges, rotor wear gets excessive.  With no other changes, I
saw a customer install RS4 (full race) into a 5ktq and trash a set of rotors in
2 days.

Bottom Line:  Know what's going on at track events.  This is extreme
environment with a street car.  Big reds aren't enough in and of themselves to prevent
heat problems in braking in these environments.  Get the IR zapper, see what
you are getting driving how hard.  Then address the heat problem.  This could
include modifying your driving style.

HTH and my .02

Scott Justusson





In a message dated 6/2/2003 3:50:49 AM Central Daylight Time,
Keith.Maddock at trw.com writes:

Steve,

You might be experiencing uneven pad material transfer to the rotor.
Spend a few minutes at the following links:

http://www.stoptech.com/whitepapers/warped_rotors_myth.htm
http://home.planet.nl/~annevelink/brakes.html

My guess is that you overheated the Red-Boxes, which don't have a very good
high temperature range.
I went through a set of those pads in my S4 (ECS Stage II)  in one day at
Wateford Hills, and would not recommend them for track usage.

However,we do have a set in the car right now, and they work great for normal
usage.

Cheers,
Keith
93 S4 (OR)
95 968CS (DE)
1/8 of a 89 Golf GTI (Ring-TOOL)