So after putting some miles on my 993TT brake coversion (full set of big reds all the way around with TT rotors up front and 930 rear) I've come to realize that I may need a brake proportioning valve to allow my rear brakes to do more of the work. Right now it feels like my fronts are getting 80% of the action with the rears just trailing along. My front tires (225) are getting overworked and I can easily lock them while my rears (295) are not breaking a sweat. Is there a factory proportioning valve I can install that will move the setup to 60/40 or somehting close?

Thanks again for the input.
E-man930

 

E-Man:

Without a doubt, I'd say that you have some brake proportioning issues with that combo,... Its FAR from optimal.

Did you install the 993 TT rear caliper with your stock 930 309mm x 28mm rear rotors?

I'd kindly suggest that you install the 993 TT rear rotors and perhaps a Tilton brake proportioning valve to you can set that that match your driving techniques.

 

Hey Steve,
Yup 993tt rears machined and tapped to use the VCI billet adaptors with new stock rotors. THe 930 rears did not look that much different size wise compered to the 993tt's... Plus I wanted to keep my parking brake.
I know I can go the adjustable valve route, is there a factory alternative. I know that when I slapped a set of these brakes on my 944 turbo, I used a 928 valve and I could literally kick the brakes and it was like the car hit an invisable wall. 930 is no where close @ this point. If I can't find a factory Porsche valve, Tilton it is.
E-man930

 

I use a wildwood valve. It's a hoot settin' it up. Luckily, I had my old track wheels/tires on it and tore up the back roads of Fayette county. Stopping power is no different from stock, but at Road Atlanta I can brake hard on each lap now - no fade.

 

Hi E-Man:

The 930 rear rotors are really too small for the TT caliper; the TT 322x28mm ones are a FAR better solution and you'll not sacrifice your emergency brake to install them.....

In fact, you might that adding more rear brake bias will add to the heat load and accelerate rotor & pad wear back there due to insufficient cooling. BTDT,....

I'm not aware of an effective factory brake proportioning valve for these cars that works anywhere near as well as the manual ones.

 

Hey Steve,
I think my rear rotors are 28mm... I know the 993tt caliper with fresh factory pads barely fit over the rotor. It was almost a clearence fit. And the top of the rotor lines up with the brake pad material. So I'm not sure how you can get a larger rotor on there without just simply moving the caliper further out toward the edge of the rotor. I'm think I'm going to pick up VCI's brake bias valve for $70 bucks or so and then try not to flat spot my tires setting it up. (I just sold a second set of wheels!) Thanks everone for the input....

Don,
how much was the wilwood valve and where did you get it?

 

I have the same setup on my car and feel your pain. While running 255/40 fronts and 315/35 rears the fronts would lock with very little pedal pressure.

Since most of the brake bias threads I've read advised against adding an adjustable p/v to the front circuit I decided to play with pad compounds.

My first change was to retain the Pagid Oranges in front and switch to Pagid Blacks on the rear. This helped out quite a bit but I still wasn't satisfied.

For my second effort I switched to wider front tires and now run 275/40 fronts and 315/35 rears. I'm using Pagid Yellows up front and Pagid Blacks on the rears and my car brakes better then it ever has... but I still think there is room for improvement.

I know a couple local 930's with the same brake setup and an adjustable p/v on the front circuit set near the first position. They say that's all it needs to achieve a near perfect balance.

 

Sureley having different compounds back to front means that at different temperatures of the brakes the bias will be different.
Guys ?

 

Fast82930,
Thank you for your input as well. What size wheels / offests are you running on your car to fit such a wide tire up front. I am planning on selling off my current setup and plan on bumping up to 315 in the rear and I would love to fit a 255/275 front... Valve on order from VCI. I'm going to stick with stock TT pads for now as the car is primarily street.

E-man930

 

I'm not sure if you are tracking/racing the car, but that size tire would be near impossible to get up to temp.

 

Nathan,

Using different pads to change bias is far from optimal. Pagid's temp / friction graph helped me decide.

http://www.pagidusa.com/pagidracing/techinfo.html

E-Man,

My track wheels are Fikse FM5's, 9.5" and 11" x 17". I'm not sure what the offsets are, my suspension shop took the measurements. Both my front and rear fenders are rolled for extra clearance. The 275's will rub lock to lock but my car is mostly track and very balanced with this setup. Under heavy braking the 275's are great.

38D,

Pacific Raceways here in Seattle has a very rough surface that is really hard on tires. This combo was recommended by my Porsche suspension pro and is a widely used combo on tracked 930's.

Lyall

 

Lyall,
That chart was interesting, as you say far from optimal way of doing things. I noticed the chart started at 100C too.