Anyone change their brake bias on their 993? The reason I ask the question is I have been getting more cracking on the front rotors than the rear. I am replacing my front rotors this weekend because they are seriously cracked while the rear is not cracked at all. The rotors are mostly track use so it seems to me with addition of a racing LSD and wider tires in the rear that I could adjust the bias a little toward the rear brakes to help on the wear of the front rotors without any issue? (Clearly front rotors cooling would help but I am working on that)

Anyone have any experience with this (Steve W, ViperBob??, Others?)

Thanks!

 

Kary:

What brakes do you currently have on your car?

What pads are you running?

 

Steve, I am using the standard brakes (not big reds) and Pagid Orange pads front and back.

 

Try some black pagids on the rear... They will give a little more bite back there and even the braking out a little more between front and rear...

 

Kary:

Bob offered a good suggestion,........

I'd follow that up and tell you something that you might not want to hear, though. Those stock 993 brakes are just too small for any track work. These cars are too heavy and have too much power for the thermal dissipation capacity of the 993 brakes. If you are running with race tires, you generate enough grip to put a huge load on those 305mm brakes and that helps overtemp them.

The real fix is to install bigger rotors and calipers that will stop the car again & again without the extreme rotor temps that are cooking the pads and rotors. BTDT, for many many years now.

Anything else is just a band-aid and IMHO, you are just fooling yourself,....... Brake cooling will help, but its never been a substitute for having a reserve of thermal capacity that bigger (322mm or 355mm) brakes affords.

 

Steve,

To your point about bigger calipers & rotors, are Big Reds big enough??? Thanks.

Rich

 

I know that I am rather biased against barking in general. Particularly small yappy little hyper active dogs that ride around in their 36/24/36 36IQ owners' purse.

 

Kary:

Back when I did my brake upgrade, I calc'd the bias using the ratio of the effective braking torque with the concept of having the same pads front and rear. The numbers seem legit. Here you go:

C2/C2S F/R: 1.55
C4S/993TT: 1.45
993RS: 1.28

Commonly installed aftermarket:
355mm F50 F/RS R: 1.40
355mm F50 (EVO) / 355mm F50 R (EVO): 1.26

Note: The larger the number, the more front bias...

Enjoy !

 

Easiest way to shift some bias aft is the previously mentioned pad compound change at the rear. You can change the rear brake overpressure valve located, I think, at the ABS controller. IIRC, there are four available from 40-55 bar. These valves are in the neighborhood of $60 from the dealer..

I, too, need to shift some bias aft as my rear rotors/pads dont seem to get the same workout as my fronts. My front rotors are cracking badly as well..

 

Hi Rich:

Its a question of degree,..(pun intended),...

The choice of brake upgrades depends on what & how the car is used and how the driver uses his brakes.

For most people, the Big Red TT/RS brake package will do the job very nicely on 993's, but IMHO TT's need the bigger 355mm ones if its driven on the track to its potential.

 

Steve, thanks for the open and honest feedback. It is not an issue of not wanting to hear it, more of an issue of staying within budget (Hans, roll cage versus bar, etc) I need to get some safety items installed first I run these rotors through an entire year of track driving. Some cooling might help them last a bit longer until I do upgrade. Though this thread was more about bias than cooling, though related, I am wondering why the rears are so clean and fronts are so wrecked. Even if these smaller brakes are too small, then the rears should have been wrecked like the fronts if they were balanced correctly, shouldn't they?

 

Good points,...... One cannot ignore the constraints made economics and the need to prioritize.

Porsche factory brake systems are all biased toward the front for safety's sake and the drawback to that is a 3:1, front-to-rear pad/rotor wear rate discrepancies. Its a function of the caliper piston sizes on both ends.

Changing brake pad compounds at the rear is a short-term solution.

 

In addition to the other suggestions, you could also uses a different p/v. A stock 993 uses a 40 bar unit on the rear circuit, a 50, 55, 60 or adjustable will be less aggressive allowing the rear to work a little harder.

The Big Reds while great(that's what I use) bump you a class, if racing.

A 993RS is ~10% more rear biased than a 993, because of the caliper and rotor combination