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Originally Posted by mohaughn  front- 4 piston forged billet superlite caliper(120-7477)- http://www.wilwood.com/Products/001-...-FSL/index.asp bore size- 1.38" 35.0 mm disc width- 1.10" 27.9mm 325mm rotor street pads- wilwood bp-10 : 4.2 to 4.6 http://brakepads.wilwood.com/02-graphs/bp10.html track pads- wilwood h-compound : 5.4 to 6.4 http://brakepads.wilwood.com/02-graphs/h.html rear brakes are stock rotor/caliper: 5.2 (I'm guessing) can't find the exact coefficient rear pads- Hawk Ceramic- hb227Z.630 I thought they were HPS on the back but they are the hawk ceramic pads.. I've had the front track pads on the car once since I installed this system. So for the most part I've been using the bp10's up front and the Hawk ceramics in the back when I've run out at sebring. I'm thinking when I start to run the track pads up front all of the time I may need to switch to a pad with a higher coefficient on the rear... I've been hesitant to use the track pads all of the time as I still drive the car on the street from time to time and they need to be warmed up to get real sticky. I'm fairly certain that UUC did their bias calculations using the bp-10 pads up front and stock pads on the back. When I ordered the guy told me I may need to play with different pad combinations to get it dialed in. But they feel great now. I see TCE has this brake bias calculator, but I don't know all of the info. Can you provide it so that we have it for anybody else to do their own calculations? Mainly the rear caliper piston size. http://www.tceperformanceproducts.co...alculator.html |
First: I do my bias calculation based on the stuff in the white papers from StopTech:
http://www.stoptech.com/tech_info/Th...%20Systems.pdf Also I have found it useful to look at the information given at these links:
http://phors.locost7.info/phors07.htm http://www.movit.de/rahmen/stoptbl.htm Second: I am working on bias calculations for the dynamic case, but have to determine some parameters before I am able to do good estimates.
The following calculations is for a static system, i.e. we do not consider the dynamic weight transfer that occur during braking. One can argue that this is wrong, but I think that if I know the static bias (i.e. how BMW designed the car), and manage to do brake upgrade that do not change the bias too much I think I can't do too much wrong. Also it looks to me that the calculator at TCE consider a static system.
What I then do is to define the bias as the ratio between the torque at the front wheel divided by the total torque at the wheels (Tf/(Tf+Tr). Then we do not need to know how hard we press on the pedal (assumed that the brake force is distributed evenly front/rear), because it falls out of the equation.
The data for the stock rear brakes are 272x10mm solid disks, and the piston diameter is 34mm (this is for my 323ti, but I think the data is the same for the 318ti). The diameter in the master sylinder is 23.81mm for both front and rear. I have found it useful to look at ATE's web site (
http://www.contiteves-am.com/generat.../index_en.html) for piston and master cylinder dimensions etc.
For the Willwood 120-7477 I have to calculate the effective piston area (Aeff=19.2cm^2 for one side of the callipper). Using a disk diameter of 325mm, and assuming the same pad friction coeff front and rear, my calculations gives that the static bias for your setup is 71.69%. The stock bias is 72.62%, and I would say that your setup is the best near-stock-bias I have seen on an after-market system. Also I do think that the slight transfer of bias towards the rear makes this a good setup (again: assuming same pads front and rear).
With bp-10 up front (.42) and Hawk Ceram. rear (.52): Bias 67.16%
With bp-10 up front (.46) and Hawk Ceram. rear (.52): Bias 69.14%
With h-comp. up front (.54) and Hawk Ceram. rear (.52): Bias 72.45%
With h-comp. up front (.56) and Hawk Ceram. rear (.52): Bias 73.17%
As a comparison, 300mm disks from e46 325i up front and stock rear gives a bias of 73.56% (assuming same pads front/rear), which is very close to your setup with h-comp front, Hawk Ceram rear and hot front brakes.
As additional info the AP-Racing I am looking at gives me 76.78% bias with stock rear, which I think is a bit too much (and is one of the reasons why I am looking for upgrading my rear brakes). With the callipper from e36 328 drop-top (38mm piston dia) and 276x19mm vented rear disk I am able to achieve a bias of 72.29%. With the same setup, but rear callipper from the e36 325 (36mm piston dia) and master cylinder from e46 325 (23.81/22.2 mm dia) I achieve a bias of 71.65%.
But based on your information given here, maybe I should try the same setup as you?
PS! Please apologize my bad english. Please also forgive my use of SI-units (1 inch=25.4mm)
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