For those that can't currently access cruz32.org:
Following yesterday's discussion, I put together a spreadsheet that calculates the Front / Rear brake distribution (among other things) based on the stock proportioning valve specs, line pressure, rotor diameter, pad dimensions, piston diameter, # of pistons, etc. etc. This allows us to examine the stock bias and the effect of larger front brake kits such as the increasingly popular 350Z Track Rotor.There are two primary assumptions used in the analysis:
- The coefficient of friction is the same at each brake pad
- The effective radius for calculating the braking torque occurs at the center of the brake pad, and the brake pad is aligned with the outer edge of the rotor (ie. Effective radius = Rotor radius - 1/2 of pad width)
Since we're using all stock hardware (with the exception of the 350Z front rotors), everything you need to do the analysis can be found in the Brake Specs section of the FSM. The OD of the 350Z front rotors is 324 mm (12.76"). First let's take a look at the stock proportioning valve. It has a split point of 356 psi and a reducing value of 40%. This means the front and rear calipers see the same pressure up to 356 psi, and above that the rears see only 40% of the increase in pressure. Which looks like this:
 The image above is NOT the stock brake bias. That's where rotor diameter, pad width, piston diameters, and piston quantities come into play. Factoring all of that in, we can calculate the front and rear braking torque at any given line pressure. The following plot shows the front and rear braking distribution for both the stock setup and with 350Z front track rotors:
 At line pressures below the split point, the stock setup has a 66.6%/33.4% Front/Rear distribution and substituting 350Z front rotors adds some front bias for a 70.3%/29.7% distribution. At 1000 psi line pressure (heavy braking), the distributions are 76.4%/23.6% stock and 79.5%/20.5% w/ the 350Z front rotor. If you look at just the change in front bias it looks like this:
 The plot above shows the additional front braking bias due to the larger front rotors. Under heavy braking (~1000 psi) you're looking at only a 3% shift in front brake bias due to the larger diameter. Whether or not this is significant, or if it's a shift in the right/wrong direction is open for discussion. If you want to review the spreadsheet and/or play with the numbers yourself let me know and I'll email it to you (or if there's a lot of interest I'll upload it somewhere). Finally if you see any errors above please let me know. PS
A few members had asked what happens if you use the 350Z caliper as well. This is the change in front bias compared to stock:
This is ~0.4% more front bias than the stock caliper w/ 350Z rotor (see above).
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