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Re: Big Red Stuff 2

In a message dated 98-10-26 16:14:27 EST, you write:

 >>Correct...you have to use a wheel spacer with some 16" wheels...5 mm or
 >>there abouts should be adequate.

Not being a fan of spacers (especially in race cars), I don't recommend at all
this avenue.  Best to do it right.   Also, spacers can create problems with
fenders pretty quickly.  Trading one problem for another.

 >>Right again...the ends of the caliper stick out a good .5" or so, hurting
>> clearance.

No Mark, it has to do with the side of the caliper hitting the spokes, not the
ends of the caliper hitting the wheel.  The caliper is too thick, not too
 > Specifically, it's the lip and the spoke design of the wheel
 > itself.  Many 17
 > in wheels are a "stretched" 16 (or even 15), which means there is
 > a step on
 > the inside of the wheel that can whack the caliper.
 >>Exactly...fortunately for some wheels, like a couple sets of Borbets I
>> the inside of the wheel doesn't have the "step"

The exception, not the rule.  Even some wheels without the step, have a spoke
design problem, Borbets included (not the "C")
 > For instance, the Groupe A (ex FIA - '95 S2) car that ran last
 > week at Lake Superior PR will take a SQ specified 15in steel wheel with
 > sport quattro brakes.
 >>That setup uses an 11.5" rotor and the compact AP 4-pot caliper.

The point is, that an 11.5 rotor and the "compact" 4 pot did not clear a 16,
but did the SQ 15's.  Just proceed with caution and homework.
> Some rims will need a wheel spacer to get the proper caliper clearance
> because of a flat backing.  Some smaller 15" wheels, like the Fuchs, have a
> curvature in the spokes so you can clear the calipers on the sides.

Maybe, depends on the size of the caliper and it's thickness.  Again, I don't
advocate wheel spacers, that's a bandaid.  When racing or performance driving,
wheel spacers are a PITA and add another item to fail, not to mention that the
length of the stud/bolt becomes really long.  Shear strength becomes a big
issue.  BTST.

 >>Here's the deal that I found out from our friend at the Porsche dealer:
>> The 993 TT has a .7" larger diameter rotor than the 928 GTS.  The 928 GTS
>> supposed to have a 12.5" diameter rotor (320 mm) which would put the 993 TT
>> caliper at 13.2", so says the dealer.  I've heard that the 993 TT uses a
>> 12.68" rotor (322 mm) (PN 993 351 045 / 046 10), but haven't seen the
>> proof...today we're going to have a 993 TT caliper and rotor and a 928 GTS
>> Caliper and rotor and see what the differences are.  The pad height on the
 >928 GTS caliper is 2.96" at it's tallest point, with some curvature in the
 >>center.  The 928 GTS caliper is supposed to have the same diameter
 >>pistons and use the same pads as the 993 TT, but is machined to take the
>> smaller rotor.  I will know for sure today...BTW, the 928 doesn't use the
>> "big reds" just as an FYI...the internals are all the same, but the
>> machining on the inside is different.

Agree, the 993tt and the 928 caliper is not the same.  My point is, that you
don't want to change rotor diameter for a given application.  You run into a
couple of problems, pads need to be custom ground for your rotor change, and
you can run out of hub trying to lower the caliper too far.  
>> One also needs to check the hat offset.  I got the shallowest hat that
>> Wilwood makes (~1.4") and the bolts that hold the rotor to the hat, rub on
>> the brake bracket ears and ball joint.  Mov'it has some shallower hats, so
 >>I'm going to see about getting one of those.  I've also got the PN for the
 >>Sport Q hats, which are pretty shallow.  That will take care of the
 >>clearance on the back side of the rotor, but in my particular case with the
>> 15" Fuchs, I'll still need to run a 30 mm spacer to clear a 12" rotor.  I'm
>> hoping to learn some more today after looking at what the dealer has.
>> case for me is that I will have to buy the Sport Q brake setup for the car.

Get your own hats machined Mark.  Then you can get it the way you want it.
Remember though, Audi tends to leave a lot of production tolerances in their
strut assemblies.  Best to bring your machinist a couple struts and take an
average.  Not sure how to talk you out of spacers for a  high hp rally car,
but I sure would like to.  Doug Shepard used to shear the 4 bolts off the
wheels in his GLH turbo rally car (1984), the main reason Dodge switched to a
5 bolt wheel for all turbo cars in 1985>.  Do it right the first time.


Scott Justusson
'87 5ktqwRS2
'84 Urq