KaiB

This is a good option, however the rear bias will be large.

I like the idea though, as it is cost effective - and the inexpensive work around the bias issue is a simple in-line bias adjuster (Tilton lever type) on the rear brake line up front in the trunk.

With the money you save, you can run RS rear rotors.

Bill Verburg

There are 2 things wrong w/ using 965 rear on 964
1) the 965 rear rotor is 28mm the 964 is 24mm, you start 2mm under the minimum thickness for the rotor
2) the caliper o/s is different and will be tougher to center on the rotor, 1 side will extend more than the other

there are 2 things wrong w/ moving the 964 fronts to the rear
1) the front rotors are 28mm the rear are 24mm, min spec for the front is 26mm, when you use them in back you start 2mm under the min spec
2) the torque bias goes to 1.008 w/o p/v 1.867 w/ stock p/v above 55bar line pressure. Stock is 1.734 w/o and 3.21 w/ the stock 55bar p/v. Just my opinion but ~1.5 or a tad lower is where you want to be. But it depends on the driver and setup and use as well. As w/ the 965 rear the caliper o/s is off making it more difficult to center the caliper on the rotor.

I'd model any changes along the lines of the RS, where if you use 964t front calipers/rotors you use 993rear calipers(they had different part #s but are otherwise identical) on 964rear rotors, the Cups did the same but also removed the p/v. bias for 964t f/993 r, is 1.713 w/o and 3.171 w/ the stock 55bar p/v. This is still a bit far front for my taste but it does work well enough

Bill Verburg

964RS rear rotors are the same as 964 rear rotors except that the have a 968 part # and have holes that are stress risers and thus be more prone to cracking

KaiB

My point is the FACT that it can be done, that it can help save money...and also allows a custom rear bias which can be easily adjusted to track and tire specifics.

And yes the RS rotors are drilled. That's the reason they are RS rotors, and they...

look cool!

HiWind

thanks Bill & Kai - dream team for this question!
Oh and on the Drilled rotors .. Meh .. Who wants those cracks/dust hideouts - I go with the grooved ones anytime I can
... quite a fan of Giros on the GT3 actually from a weight and durability pov

And thanks Bill - your measurements make the problems clear:
Backs: 964 front calipers on the 964 back rotor - can I solve this by putting on a bigger rotor?
Fronts: 965 Caliper on 964 front rotor - they're both 28mm no? So that should be fine?

Kai: I'm keen to try more rear bias ... and even considering the adjuster you spoke about ...
but could put it on the dash ala the lightbau

KaiB

Wind, check with Steve Weiner regarding a 299x28 solution to the rear rotor.

I believe he was checking into a 2 piece AP racing/Alu hat for mine (when I can afford it). But you can forget the parking brake (I will say it is a bit of a hassle not having it, even in a full on race car).

I replace rear pads when I do the fronts (every other race weekend) so I don't worry about the 24mm rear (i.e. over extending the pistons).

Too much rear bias is FUN!!!

Bill Verburg

there is no bigger rear rotor unless you give up the parking brake, if you do you might is well use the 993RS rear caliper, the 965 uses a 299x28 w/ the wrong o/s for a 964, you still have the bias issue

you have to use a 322x32mm caliper in front w/ 965t or 964RS front caliper or w/ 993RS/tt front caliper, the 993 front or 928S4 can get away w/ a 304x32.

the o/s of the 964 and 993 rotors is different, so be careful choosing components, w/ 993 wheel carriers use 993 rotors, w/ 964 wheel carriers use 964/965 or 928 rotors w a caliper adapter w/ correct o/s for 964 parts, you could use 993 rotors but then the caliper adapter needs 993 o/s, w/ 964t/964RS wheel carriers use 964/965/928 rotors(no caliper adapter is needed)

This is Geoffrey's car, 3222x28 AP rotor annulus/Wrigtwood hat, 993RS rear caliper,

w/ 964t front and this setup in back bias is 1.472, 993RS/Cup/RSR similar setup is 1.426. I know Geoffrey wanted less rear and we talked about drilling 993tt to be 30/34 instead of 28/28(RS is 30/36) but don't know if he followed through.

I have the RS/Cup set and think it's great, w/ good balance, reduced front temps and inc rear temps

if you retain the parking brake(they are great for trailering if nothing else) then best advice if you use 965front calipers and rotors(or 993RS/tt) use 993 rears on stock 964 rear rotors and ditch the p/v

cobalt

I have run the 993 rears with big reds up front and now am using the 94 turbo rears and as stated you loose the parking brake if you go this route. Heat dissipation and braking is improved with the turbo rears but not enough to loose your parking brake for street use. I do not street my car.

HiWind

thanks guys - I was hopeful I could move the front 64 caliper & rotor to the back
and then get a nice big front rotor to suit the 65 front calipers ... didn't think of the parking brake...
which I don't want to loose .. oh well, seems best option is just to buy some late 64 rear calipers

ie back to the drawing board

KaiB

Nah, do what Bill says and get Big Reds (Blacks) over nice rotors up front and put 993 rears in the back - loose the p/v and you're close enough. This way you retain the parking brake also.

For track use then you could adjust the bias with different pads (i.e. Pagid yellow front / black rear).

HiWind

what about 930 Turbo rears? I think I'm better off with the 993 C2 rears, right?

Bill Verburg

right!
use stock 964 rear rotors or if you want drilled 968 M030 rear rotors(same as 964RS)

HiWind

sorry I mean caliper Bill! Still true?

KaiB

I'll jump in for Bill, if OK.

Yep, the 993 calipers.

HiWind

thanks again Kai!