[spuggy]

Originally Posted by 911st

What dose it take to mount a C2 Caliper on a 3.5" spacing Carrera strut if used with 24mm Carrera front rotors?

There seems little point in putting bigger calipers on a 24mm 3.2 front rotor, because tire adhesion and thermal capacity of the rotor are the limiting factors.

The 3.2/SC calipers make 88% of the front braking torque of the 930 setup, on a rotor with 54% (SC) or 65% (3.2) of the front volume of the 930 setup (and thus thermal capacity).

Which is why you can overheat the 3.2 rotors with 3.2 calipers, let alone putting bigger, more powerful, calipers on the 3.2 rotor. And 3.2 calipers will lock the fronts, so "feel" (can be related to caliper stiffness, and/or pad area) and thermal capacity are the main reasons to upgrade.

The C2 calipers are designed to run with 298x28mm rotors, and these have a different offset to the 911 rotors. Bill V has written a lot of stuff here about the 964 rotors/calipers. The C2 setup has 98% of the torque of the 930 setup, and 88% of the 930 rotor volume (thermal capacity).

(I've long thought that the 930 setup is overkill in terms of thermal capacity anyway. It was off-the-shelf stuff for the 917 after they realized the 3.0 930 brakes turned to chocolate too quickly- but the 917 was an endurance racing car...)

If you fit 964 calipers on 3.2 rotors, there may be an issue with the pistons over-extending if the pads wear thin. Or not. Swept height of the C2 pad appears to be less than the 3.2/SC pads, so there shouldn't be an issue with pad overhang.

On the other hand, the 3.2 rotor is designed for a taller pad. So that might be an issue - you'll certainly not be putting that extra braking torque across the entire radius of the rotor.


C2 and 944T (and some 928) calipers are the same "basic Brembo", IIRC (gosh, I miss Bill V's brake page).

VCI does a kit to convert them for 911 use. Which includes making adapters for the calipers, because the 964 rotor offset is wrong for the 911, and the calipers work with that rotor.

Most people figure that it costs so much to adapt these for use on a 911 - and they're still lower spec than 930 brakes - that you might as well skip straight past them and get really serious (993TT, 996TT, Brembo GT-X) brakes for that same money that bolt straight on and definitely won't ever overheat.

Me, I think 996 are my sweet spot. Light, stiff, cheap wear parts and very close to 930 numbers for rotor volume, piston area. Far more swept pad area, IIRC. I just wish you could hog out the rear caliper pistons for slightly more rear bias.

Will this clear a standard 7x16" Fuchs?

If they're the same as 944T (951) calipers like I think they are, and the 951 Fuchs have extra space (and their own part #) to clear the calipers, I'd guess "probably not"...

Will a C2 front rotor bolt up to a Carrera 3.2 hub?

Believe so, but I seem to recall reading that the offset is wrong? It also gets very close to the A-arm, and you have to space the wheel or grind the A-arm.

IIRC, the '86 (pre-ABS) 944 turbo front rotor bolts up as well. It's the same dimensions as the C2 rotor.

Is there any difference between a C2 and C4 front caliper?

Fronts are the same between C2 and C4, at least in terms of pad dimensions, rotor and piston sizes.

Would a turbo MC be needed on an 85 Carrera.

If you need a 930 M/C for 930 brakes (which most people seem to agree you do, then "yes".

C2 front caliper piston area is in 930 territory (C2 is 2274 mm^2 as opposed to 2268.23mm^2 for 930 fronts), and the 3.2's single 42mm rear piston is 98% of the 930's rear piston area (1385mm^2 as opposed to 1413mm^2).

Should the rear pv valve need to be removed or any advantage to replacing w an adjustable?

Based on plugging your combination into my brake bias spreadsheet, I believe you should remove the P/V. It's about the same front bias as a 964RS, and more front-biased than a 930 (neither of which run a P/V).

See for yourself (these values are with the same coefficient of friction pads front and rear):

Anyone know the difference in pad area from Carrera to C2?

It looks like the C2 front pad has a working pad area (not including the backing plate, just the friction pad) of 98mm x 45mm ~= 4410mm^2.

As opposed to the 3.2/SC pads, which have a working pad area of 61mm x 54mm ~= 3294 mm^2.

But swept pad area isn't the issue.

What problem are you trying to solve?