Lemming

This year I upgraded my car from 924S spec (nearly) to 951/968 spec all around. Couple this with an increase in tire/wheel size from 245/15 to 275/17 and my braking has increased dramatically. Last year my major competitor was able to out brake me with ease, this year I can out brake him (and many others). However, a few of my fellow drivers think I can do even better with the addition of 951S front calipers and rotors. Any informed opinions?

Other info that might be of interest.
Car - see avatar.
Car/driver weighs in at 2640 (currently porky, will be 2510 for next season).
Brakes pads are Hawk DTC60 all around and is well balanced, front rotors have cooling ducts, rears do not.
Tires - Hoosier R and A6's.

smlporsche

Tim-
I have the 951S (928 S4) set up in the front and love it. With the 245's up front it provides me with a fairly balanced package. I also upgraded (changed) the brake bias valve to the 951S with more rear bite.

My car weighs 2650# and I don't have the 968 power (yet) so given your configuration I would definitely say it would be worthwhile.

Lemming

How quickly do you go through front pads? Price is a consideration as the 951S pads are about $100 more per axle set

smlporsche

I'm running solid frozed rotors with PF97 pads.
I can get 4 or 5 weekends out of the pads. Maybe even more. I don't really keep track as I just have a spare set in my trailer and put them on when needed.
The frozen rotors have lasted a season and a half.

Larry Herman

When you can still lock the front brakes (or trigger the ABS) at the end of the stint, if the brakes remain consistent once they get up to temperature, if the pads and rotors last a reasonable amount of time, then I'd say you have enough brakes. Any more (larger calipers & rotors) will not stop you any faster, and will just add weight.

Lemming

I have had some fade when I run 3-hr endurance races. Generally no problem with sprints until this past weekend at CMP where I did experience some fade near the end.

Van

You can always change back, right?

But I think you're going to like them.

Lemming

I already have the calipers, found a good deal that I just couldn't pass up earlier in the year, you know, just in case I still have to buy the adapters, rotors and pads. I guess it's just money

Is there any advantage of moving the front 968 brakes to the rear? Although they use the same pad, the front calipers have larger pistons.

paradisenb

Remember that CMP is the exception to the rule. It is infamous for eating up brakes.

Van

I didn't know that. Might be worth a try!

M758

more unsprung mass is bad. However better braking is good.

the question is does the increase in mass counter the braking? Like Larry said braking performance is mostly about heat managment. Larger rotors and pads allow you store more heat to keep overall temps down. Slowing down better is a result of braking and other things. Pads, Pad thickness (new vs old), operating temps, tire contact patch and as result suspennsion settings.

You maybe able to improve braking by changing the alignment and or spring rates. Larger brakes in front won't change that (except for unsprung mass), but wil give you more heat capacity.

Oddjob

The 928S4 calipers have 44 and 36mm pistons compared to the T/S2/968 front calipers which have 40 & 36mm pistons. So you will gain approx 12% more stopping power vs the standard T/S2/968 from the calipers alone. The rotors are just a hair larger OD, so you will also pickup a small increase from the slightly longer torque arm. Not sure of a direct correlation between stopping "power" and stopping distance, but I am certain that the same car with 928S4 calipers will have somewhat shorter stopping distances.

Also, the calipers are physically larger, the rotors are thicker and have directional vanes and the pads are quite a bit bigger, so they will absorb/dissipate more heat and be more fade resistant than what you currently have.

The T/S2/968 rears have 30 & 28mm pistons - so the fronts have 1.7 times greater piston area, which means the calipers will generate 1.7 times more force on the pads. Reality - that is too much, it will throw off the brake bias and the rears will lockup first, even with the 928S4s on the front and the 18 bar bias valve. Might balance better if going to even larger fronts, like big reds or big blacks.

I recall the caliper bolt pattern is not the same front to rear, so the fronts cannot be mounted on the rear trailing arms without some sort of machined adapter. I am not aware of any off the shelf adapters available to mount front calipers on rear trailing arms, but they might be out there somewhere.

Lemming

Thanks guys, good info.

Land Jet

What brake fluid are you using? That could contribute to your fade. I never cared for the Hawk pads, like Pagids myself, but have you tried other pads?

Van

Jim, your knowledge never ceases to amaze me!