24mm Carrera Rotors with S Calipers

RallyJon · 07-16-2004, 11:07 AM

Anyone done this successfully, without machining the rotors down to their wear limit?

From searching the archives, issues seem to be:

a) Later S calipers (Carrera RS style) may have different internal clearance than the early (906 style) ones. Anyone know?

b) Have to use the thinner SC pads, rather than the thicker S pads. Makes sense--that 4mm has to come from somewhere.

c) The 24mm rotor may have an offset centerline compared to the 20mm rotor. Anyone know?

Basically, anyone got proven BTDTs? Thanks!

Shuie · 07-16-2004, 11:13 AM

Check out Warren's response in this thread

911pcars · 07-16-2004, 11:19 AM

A European Car mag. article from a few years ago tackled this mod. They machined the throat from the S calipers to gain the needed space. Not recommended. Maybe there is a different version of the S caliper that won't require this? Maybe others know. SC pads (thinner) for sure.

Sherwood

RallyJon · 07-16-2004, 11:31 AM

So Shuie, did you do it?

I saw that thread, and other one had a comment by Bill V that some fit, some didn't.

Thanks for the lead, Sherwood. Not much on their web site, but I sent an e-mail to the back issues department.

Shuie · 11:43 AM

nope, I bought the Carrera calipers, rotors, and a new master cylinder. Sold my S calipers off in less than 5 minutes on the for sale board.

The car stops real good

. I've read that the Carrera setup is considered and upgrade for the track. I honestly dont think I have seen a difference between it and the S-calipers setup for street driving.

KobaltBlau · 07-16-2004, 11:54 AM

Quote:

Originally posted by RallyJon
c) The 24mm rotor may have an offset centerline compared to the 20mm rotor. Anyone know

Yes. this is because the inner half of the caliper mounts exactly the same between SC and C3.2, and the spacer between the two halves is simply wider. I'm sure you can get away with a little offset, but it's not ideal.

RallyJon · 07-16-2004, 12:44 PM

Quote:

this is because the inner half of the caliper mounts exactly the same between SC and C3.2, and the spacer between the two halves is simply wider

If that were true, then the S caliper wouldn't be centered over the 20mm rotor, right?

Bill Verburg · Bill Verburg's Garage

Quote:

If that were true, then the S caliper wouldn't be centered over the 20mm rotor, right?

Just use the S w/ the 20 or a wide A w/ a 24. why ask for trouble?

KobaltBlau · 03:37 PM

Quote:

Originally posted by RallyJon
If that were true, then the S caliper wouldn't be centered over the 20mm rotor, right?

No. I was trying to say that the center plane of the 24mm disc does have a different offset from the center of the car compared with the 20mm, because the inner mounting of the caliper did not move inward (it didn't move at all) when they widened the rotor. only the outer side of the caliper went out. Does this make sense? Sorry I re-read my previous reply and the
explanation sucks.

oh, and Bill's right. Wide As are pretty cheap even new. See my recent thread for the tribulations of buying wide As used, you'll want to buy new

Bill Verburg · Bill Verburg's Garage

Quote:

the center plane of the 24mm disc does have a different offset from the center of the car compared with the 20mm

No it does not. All the additional space on the Carrera caliper comes from the center spacer.

RallyJon · 07-16-2004, 09:27 PM

Quote:

why ask for trouble?

LOL! If I didn't want trouble, I'd have given up on this damn thing when I found the first sign of rust.

Seriously, thank you for all your input and knowledge on this topic even if the discussion veers more towards the speculative than the sensible.

Looks like it was the October 2002 issue of E.C. if anyone has a back issue lying around.

911pcars · 07-16-2004, 10:42 PM

Bill writes:
"Just use the S w/ the 20 or a wide A w/ a 24. why ask for trouble?"

Bill,
That's because being able to fit 24mm rotors into S calipers would be nicer than 20mm rotors and without the weight penalty of the wider but heavier iron As (despite the potential flex nature of the lighter Al calipers).

What if 24mm rotors are ground thinner to fit inside an S caliper (e.g. 22mm)? Would this be a better heat sink than a stock 20mm rotor or are the vent holes larger in the 24 which results in a thinner 24 having less mass than a new 20?

I could take a look as I have both sizes buried somewhere in the garage, but I respectfully ask you, the brake guy out of my sheer laziness to locate them tonight.

Regards,
Sherwood

Bill Verburg · Bill Verburg's Garage

Quote:

That's because being able to fit 24mm rotors into S calipers would be nicer than 20mm rotors and without the weight penalty of the wider but heavier iron As (despite the potential flex nature of the lighter Al calipers).

Sherwood , I understand that. Its just that even though if you jump through enough hoops you can do something, it doesn't necessarily meant that you have accomplished anything meaningfull. I have had the benefit of working closely w/ factory Porsche mechanics and engineers for many years. The reason they stopped using the S caliper for weight reduction was when they found that the variance in tires was more than the weight savings of aluminum calipers.

Yes, I have seen the S calipers on the 24mm rotors, the question becomes how worthwhile is it. Some folks enjoy the challange more than the result and that is a good enough reason as well

Quote:

What if 24mm rotors are ground thinner to fit inside an S caliper (e.g. 22mm)? Would this be a better heat sink than a stock 20mm rotor or are the vent holes larger in the 24 which results in a thinner 24 having less mass than a new 20?

That falls into the same catagory, yes it can be done but what is the meaningful benefit. Again for those that enjoy the challange, do it

I have found that a ~2000# and ~200 hp S calipers on the 20s is fine, w/ approprite cooling, pads, fluid etc.

~2400# and ~200hp the Carrrera setup is similarly adequate.

This is for track use for 20 - 30 min stints on a moderately brake intense track like LRP

Bill Verburg · Bill Verburg's Garage

Quote:

Looks like it was the October 2002 issue of E.C. if anyone has a back issue lying around.

If that was the series on the 911S builup, they wanted to use the S caliper w/ 24mm rotor but ended up w/ the Boxster caliper on the 24mm Carrera rotor. For the back you will want Carrera wide Ms on Carrera 24mm rear rotors.

KobaltBlau · 07-17-2004, 06:06 PM

Quote:

Originally posted by Bill Verburg
All the additional space on the Carrera caliper comes from the center spacer.

I agree, but doesn't this push the center of the spacer out from the center of the car, since the spacer is larger, and the inner mounting is the same? That would push the center plane of the break disc out as well, right?

Bill Verburg · Bill Verburg's Garage

Quote:

doesn't this push the center of the spacer out from the center of the car

Yes, I never thought this all the way through. The rotor needs to have an additional o/s = 1/2 x the D of the spacer thickness

Bill Verburg · Bill Verburg's Garage

Which presents an additional reason not to try to use an S caliper on a 24. All the meat would need to come from the out board face of the caliper throat.