[Dave-ROR]

Originally Posted by eikond

Dave: Where did you read that WRX 4-pots suck? Have you tried them? I've read one review on this forum where the guy said he loved them. Where did you hear that they move the bias toward the rear?

Piston area is smaller, which means less brake torque at a given pressure (which with no other changes is constant for our purposes). That means that given the same rear setup in both cases, bias will shift towards the back. I meant suck for this (and the WRX) application, not that they suck for any other reason (ie, high flex, crap seals, poor construction, et cetera).

Originally Posted by eikond

Here's my math:
The stock BRZ calipers have 48mm pistons
if my high school geometry is correct, that would make for a radius of 24mm. Pi x R ^2 = 1810 x 2 pistons = 3620

The Z32 calipers have 40.45mm pistons
same math gets me 1282 x 4 pistons = 5127

It actually doesn't work like that for piston area on a slider. You measure only one side of both calipers. If you want to measure both, you'd just double the OEM ones (so 7,240 based on your math for the WRX calipers).

Originally Posted by eikond

So, in theory the Z32 caliper should inpute more clamping force right? So I'm not sure why that would result in moving the brake bias toward the rear?

Again, i'm not a physics expert..

Based on the correction above, the piston area is actually smaller than stock, so it'll shift towards the rear if all else is equal. Until now all the comments I said about shifting towards the rear was directed at the WRX calipers as I didn't bother to lookup the Z32 ones. Given the better leverage though it could be a wash (leverage = further from the hub, no different then using a longer lever to apply torque to a bolt vs a shorter lever)

Originally Posted by eikond

One thing I noticed is that the Z32 pads are slightly smaller surface area than the BRZ stock pads. I don't know how much smaller though.
Does a larger pad surface area increase stopping ability? It seems logical that it would.. but I'm not sure about that.

Swept area does have an effect combined with pressure and piston area as well as leverage. However, brake force by itself isn't the issue (OEM calipers have PLENTY - they can lock up R compounds so an increase is force is simply not needed). A potential change in brake bias can lengthen braking distances due to easier lockup (more ABS intervention). This assumes Subaru did the job correctly and optimized the bias as well as they could, which isn't a sure bet given the parts bin nature but clearly they tried (hence the LGT rears with the WRX fronts vs all LGT or all WRX, etc). Prop valve/abs pump/etc play a roll in that tuning as well so we should assume that it's at least pretty good from the factory.