qfrog Ti20

So I've wanted considerably larger rear brakes for a couple of years now. I even had a set of custom aluminum brackets adapters made up and in that process a set of new rear carriers were sacrificed... didn't fit properly, fell through and I've been waiting eagerly for something to come along and take the place of the brake setup I never got to see to success. I wanted originally to run 302x12 rears from the C6 A6... I had my eye on the rotors back in 04 when I first saw a pre production C6... this dates to just after I came up with the 255x10 setup.

Last week 034 made available some caliper carrier spacers made from steel intended for use with 300x22mmm Rear rotors from the B6/B7 S4. I wasn't even sure if they would work with what I had in mind when I ordered them but I figured they are affordable and if I don't use em... no major loss.

I have yet to test fit the setup but the measurements indicate a high probability of these brackets being compatible with the B7 A4 quattro's 288x12mm rear rotors.

How?
The oveall height of the B5 A4 quattro 245x10 rear rotor is the same as that of the B5 S4 256x22. The thicker portion of the B5 S4 rear rotors faces outwards... so the vanes and 2nd friction surface extend outwards towards the top of the rotor's hat. This means the inside of the caliper... piston side... is essentially in the same place in relationship to the knuckle laterally... not radially. Radially the S4's calipers are spaced about 5.5mm farther out from the axle by direct comparison to the B5 A4 quattro's. The caliper carrier has an extra wide opening for 22mm thick rotors... just as the caliper is wider to accommodate the 22mm rotor.

The similarities between the B7 A4 quattro rear rotor and B6/B7 S4 rear rotor parallel the similarities between B5 A4 quattro rear rotors and B5 S4 rear rotors. The rotor is thicker but not taller and thus the inside facing of the rotor is in the same place laterally between B7 A4 quattro and B6/B7 S4.

So while the B5 quattro rear rotors use a different hat height from the B7 A4 quattro and the B6/B7 S4... the 034 caliper carrier spacers make up for the difference in hat height and increase the reach of the caliper carrier.

So what am I getting at... Monday when my caliper carrier brackets arrive from 034 or so I'll get to test fitting 288x12 rear rotors to my sedan... this setup would use stock B5 A4 quattro rear calipers, carriers and pads. I may have the rotors cut down to 10mm by the machine shop... might cost me $50... but actually the stock B5 A4 quattro caliper carrier opening is 12mm so just half a millimeter from either side of the each 288x12mm rotor is enough to provide clearance.

So am I going to fvck up my bias... maybe maybe not... the 8P A3 uses 312x25mm fronts with 286x12 rears. The A3 has a similar overall mass but with worse weight distribution than my sedan. I am not certain of the piston diameter on the A3's rear calipers. The B7 A4 uses 321x30mm fronts with 288x12 rears.


How much should this end up costing... less than 255x10mm rears. Caliper Carrier spacers are $85 shipped... Rotors are 70-80 each... add in a little bit for some thinning out and maybe the total is ~$300.

Update on Monday evening.

thewatcher101

why not 034 300mm rear upgrades

qfrog Ti20

The incremental difference easily pays for half of a larger set of front brakes. The money might be more effectively spent elsewhere.

I think I'm going to spend a total of $175 on parts for this upgrade. To use the 300x22 rotors I'd be in for more like $635 in parts.

thewatcher101

the s4 guys like their stoptech rears a lot


just got to hunt them on the FS tread

slightly disgruntled

Is there a FS thread or did you mean classifieds

qfrog Ti20

Car-part.com has none listed and used pads go in the **** can.

The B5 S4 calipers are scarce and I can achieve nearly the same effect for less $$$ with only new parts. Besides this is likely more rear brake than the car warrants. I suspect ABS will be doing it's job to keep the rears from locking up on road courses with just 288mm rear rotors.

thewatcher101

naw - i mean other forums - our classifieds move like a snail

urs6_ma

What are you running on the front?

I'm upgrading my '01 a4 avant with a BIRA System 2 in the front -- 322mm S4 rotors, 996 C2 calipers.

I was planning on going with and S4/A8 rear setup. S4 calipers, A8 rotors (269mm?) and A8 caliper carriers. Only pricy part is the A8 carriers, which are about $150 each new, if you can't find them used. The S4 calipers are pretty readily available used at $65 a pair.

The increase front/rear is almost even, with *slightly* more increase front percentagewise.

Your approach is significantly less expensive and I'll bet the 288x12 rotors are much lighter than the 269x22 A8 rotors!

Only issue as I see it is that with my move to 322mm rotors front, a proportional rear rotor would be 275mm, which suggests that the A8 rear rotor is a better match for the S4 front (but I don't know what front brakes you're running...)

Curious to hear what you learn...

audiTaxed

Was this successful?