Quote:
Originally Posted by Daemonblitz
I don't have or claim to have anywhere near the experience that that some of the track junkies here have. Which is why I brought this is up for discussion.
Maybe it's me being a bit thick, but from what you are saying I am gathering that the piston surface area needs to be within 10% smaller to see an improvement ? Well just with the fact that it is now 4 piston instead of 2 piston on the front, that surface area would be almost doubled (right?), At the same time however the surface of the pad is smaller than the OE pad so the contact patch between the pad and rotor would still be smaller.
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Unless you have the actual piston diameter, you won't know whether or not the piston surface areas are bigger or smaller.
Take the 6 piston caliper in the 135i for example. I happen to have the piston diameters on hand, because I asked my buddy who races one long time ago when someone were interested in getting some take-offs from the 135i and custom fabricating a bracket to fit it on his 335i. I did the calculation for him to show that the 6 piston calipers on the 135i has a significantly smaller piston surface area than his sliding 1 piston caliper OEM set-up and would result in the brake pedal being so insanely stiff that you wouldn't be able to push it past more than it's 1/2 travel point, and that such a system would be hazardous to drive because it's impossible to modulate the brakes.
Just for sh*ts ang giggles, I'm going to repeat that calculation for the thousandth's time, but this time, I'm going to do it against the front calipers of the MZ4 Coupe. The MZ4 Coupe has a sliding caliper with a 60mm diameter piston. The 135i 6 piston caliper has a progressive caliper piston diameter of 28, 32, 36mm. The MZ4 number I can pull out the back of my head. It's 2827mm^2. The 135i I will have to calculate again, but it's simple. It's ((D/2)^2) * Pi, or Pi*r^2. Given the 28, 32, and 36mm diameters, the overall clamping side piston surface area of the caliper on the 135i is:
(14^2)*Pi + (16^2)*Pi + (18^2)*Pi = 2438mm^2 (no you do not calculate all 6 piston, the ratio of slave pistons to master cylinder is per CLAMPING SIDE ONLY)
That's a 15% decrease in piston surface area, which, like I said, will lead to a rock solid and useless brake pedal.
Here's a thread where I installed the RacingBrake 4 piston front, 2 piston rear caliper upgrade kit for the MZ4 Coupe, in it I also detailed how piston surface area affect pedal feel in a sliding vs. fixed caliper system:
http://www.zpost.com/forums/showthre...ht=RacingBrake
RB's 4 piston calipers measured with a progressive piston setup of 38mm and 44mm. Unless you an find out what the piston surface area is on the kit you're looking at, and do the calculations above, *I* wouldn't touch the kit with a thousand foot pole.
But it's your choice. You can easily go in blind and hope that BMW uses the same ratio of master cylinder for ALL their cars, which, actually, has been the case for the last 20 year or so of non-M 3 series. Although, even within the same 3 series family, there are variations between M and non-M models, and even with M models, the ZCP and the nonZCP E46 M3s have different sized master brake cylinder.
Last thing I will add. If you don't care whether or not your brakes function properly, feel free. I have absolutely zero objections for you to modify your critical safety system on your car, provided you don't live anywhere near me or share any of the same roads I drive on.
