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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
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
>>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.