Ok,I realize that the front brakes do most of the work but my big reds have now used up 2 sets of Pagid orange. The rears have not used even .5mm of pad. I changed out the stock proportion valve on the ABS module with the correct part from the Turbo when I did the upgrade to the big reds. All use of the Pagid pads have been on the track. I am about to buy my 3rd set of fronts and am thinking there must be something wrong with the rear calipers, not catching??? is this normal 3 to 1 wear?( at this rate I will get 7 sets of fronts to one rear) I bleed brakes after every track day and change fluid after every other track weekend using ATE blue/gold. Thus far, 1 set of fronts have lasted 10 track days and are below spec (wear groves on pads are gone) Anyone running Pagid orange for the past couple of years please respond

 

Try an adjustable p/v or use one with a lower knee. The knees available as Porsche oem are 33, 40, 45, 55, 60(there are also probably others I haven't run into). The lower the knee the less rear brake is applied once the knee line pressure has been reached. All reduce rear line pressure by 46%

A good starting point would be the 993 RS which used the 44/36 Big Red on a 322x32 rotor front with 36/30 S4 size rear on 322x28 rotor with the same 40bar p/v as your 993 oem. The bigger rear pistons naturally move bias a bit to the rear for a hydraulic bias ratio of 1.472below the knee, 2.725 above the knee

Another good guide is the 964 3.6 turbo, same front brakes with34/30 rears on 299x28 rotors with a 60bar p/v HBR = 1.572 below the knee 2.911 above the knee

 

Thanks Bill,
So the stock p/v from the turbo must have a lower knee (I have not heard that term below) I will check the part # and see if I can get a higher value p/v. For track applications, I want the rears to do more work. I think the big reds have more stopping to give me that I am getting now.

 

Hey Eric!

You forgot to mention how you were running all the 964's off the track at Gingerman with your Exhaust by Robin and Big Reds! I'm surprised your pads lasted as long as they did.

Good to see you last weekend. Thanks again for letting me check out your seats--they're definitely on my list.

BTW, we are running a similar thread on the 964 board--swing by and check it out. It's called "Brake upgrades - again." I asked a similar question since I crushed my front pads at the track as well. Bill V. and CupCar provide quite a bit of good technical information which expands on his earlier point.

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

Eric,
Are you using TT brakes front and rear? I use Pagid orange on my stock 993 brakes, and get about 3/2 F/R brake pad wear. Your ratio seems excessive, even on a brake consuming track like Gingerman.
By the way, I still hope we meet sometime there. Sounds like you're pretty quick.

Chuck <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

 

I believe that Erics car has 30/34 rears(at least thru 95 that's what they used on the back of a 993 oem). If he were to go to 993TT rear brakes which are 28/28 that would put even more of a load on his front brakes(more front bias).

As Chuck has said the Big Red front with the stock 30/34 rear is a good combination. The front piston area is the same as stock, the pad area is ~21% greater, dispersing the thermal and mechanical loads over a wider area and the 322mm rotor has an ~6% longer lever arm.

The 2 things that you can do to move more brake to the back are the p/v with a larger #(or an adjustable one) or the 993 RS rear calipers with 30/36 pistons. These RS calipers are S4 size using the same pad is the oem 993 front. Both the extra pad area and the larger piston area move bias to the back.

The 993 C4 does use an S4 size caliper but with small 30/28 pistons. The pad area is the same as your old oem 993 fronts but the small pistons move the bias further to the front(somewhat compensated by the larger pad area)

 

Thanks for the advice guys. Bill, I have Big Reds all around, when I changed my pv to the turbo valve, I put in a 55 bar valve. I cant believe that a 60 bar will give me even rear braking but I am going to give it a shot. Joey B, I checked out the thread on the 964 board and followed a link to a guy that by passed the pv but was overheating the brakes, tempting as the bypass seems, I dont want to start stocking rotors. I think there may be a problem with my system, I may take it to the dealer to put the system on the Hammer as my race shop keeps telling me there is nothing wrong. Chuck, the car is fast and set up very nice, I'm just along for the ride As fast as I sometime think I am, I was humbled when the starter sent me out with the A group. I know these guys have race cars but I felt like I was driving a jetta I will post my results of the pv change and the dealer visit.

 

Eric its critical to kow what calipers and pistons are installed along with what rotors, p/v and pads.

There are only 3 sizes of Brembo caliper. In order from largest to smallest(color is really irrelavant for the purposes of this discussion)

There is only 1 Big Red caliper it has 44/36 pistons, radial mount, 151sqcm/caliper pad area and should be used with a 322x32mm rotor

There are several versions of the the S4/993 caliper in radial and axial mount, pistons available are 44/36, 36/30, 34/30,30/28, 28/28 and there may be some others used on water cooled cars. All use 125sqcm/caliper pads. Some were used front with 32mm rotors some were used rear w 28mm rotors

There are several versions of the basic Brembo caliper all are axial mount, pistons available are 40/36, 34/30, 30/28, and there may be some others used on water cooled cars, all use a 86sqcm/caliper pad area. The fronts may be used with 32mm or 28mm rotors the rear with 24mm or 28mm rotors.

The real experts here are Steve Weiner at <a href="http://www.easystreet.com/~porsche/" target="_blank">Rennsport Systems</a>

or

Mike Wacholz at <a href="http://prospeedmotorsport.com/index.htm" target="_blank">Pro Speed</a>

 

Bill, you really know way too much about brakes The brakes I bought from 911 design were factory porsche "big reds" If I assume that it has the proper 44/36 pistons (not sure how I would measure it) I am going to call 911 design to double check the specs, if they are indeed the
44/36 pistons with the 322x32mm rotor then would the 60 bar pv give me the improvement I am seeking?

 

The real issue is what's on the rear. oem 94/95 993 is 30/34 basic(smallest) Brembo on a 299x24mm rotor, using the smallest Brembo pad. Did you replace the rear caliper and/or rotor? If so, you need to know what size pistons(30/34,30/36,28/30, 28/28) rotor(299x24, 299x28, 322x28), pads(biggest"Big Red", medium"S4/993frt",smallest "basic Brembo", are in use.

 

Bill,
rear is 322mm rotor,I dont know what the piston size is but would assume it is the same as a 96 993 stock turbo caliper (as it was not the racing brake upgrade)

 

Assuming that it is the stock 993tt 28/28 on a 322x28 rotor in the back and that the front is a Porsche(not after market) Big Red Brembo 44/36 on a 322x32 rotor. The front pads are the 151sqcm/caliper front and the rears are the 125sqcm/caliper.

Your basic hydraulic bias ratio has gone from 1.572 stock to 2.061, any p/v will increase the front bias. The stock set up goes to ~ 2.9 when the p/v is fully active, the setup on your car goes to 3.817. The higher the HBR the more front brake will be used. All the p/v have the same 46% reduction factor, only the knee changes.

Bottom line, its no wonder the front pads are being used up rapidly when the car is driven agressively.

I have often wondered how the 993tt gets away with such large front bias, I can only assume that the large rear weight bias and ABS programming take care of any hbr issues.

The best you can do to get more rear brake w/o buying new rear calipers is, remove the p/v completely

 

Thanks again Bill. I will check with some of the local racers as to what they are running. short of going to a Tilton set up or something more exotic, this may be a problem I have to live with.
From your last post, moving from a 55 bar valve to a 60 may not do anything, or will it get me a little more rear brake?

 

Going from 55 to 60 will give you a little more rear brake. You are so front biased that total removal is probably called for.

Some history

• 911 Carrera and SC -83 hbr 1.596
• 78-87 930 hbr 1.604
• 964 hbr 1.720
• 964RS hbr 1.572
• 964T hbr 1.572
• 993 C2 hbr 1.572
• 993 C4 hbr 1.919
• 993RS hbr 1.472
• 84-89 Carrera hbr 1.306
• 993 tt hbr 2.061

all of the above are either w/o a p/v or prior to p/v actuation.

 

Eric -

I am running the same setup as you, except I still have the stock 40 bar valves. I am getting about 2.5 front to 1 rear on the pads. I am running rs-14 pads "blacks" though.

I just change my tire sizes so I am getting a little lock up on the rear end once in a while now. I will see how this effects my pad wear. I was also thinking about bypassing the valves completely, but I am going to run a few more events with the new tire combo first.

One thing you can do is use pagid blacks on the backs and use orange pads on the front. This will put more bias to the back.

Spring rates and/or shock settings can make a difference too.

Bill.