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Old 09-17-2005, 05:36 PM   #87
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Join Date: Apr 2003
Location: Maplewood, NJ
Posts: 446
My Ride: 2001 540i 6-Speed
Originally Posted by gbn
Regarding BBK's I agree about the force, friction coefficent, heat build-up, rotor size and racing vs. street pad issues. Good point about the brake porportioning. Most BBk's have 4 piston calipers, vs. 2 piston OEM. Other than more even braking force, does anyone know why they do it?
Actually, most OEM calipers have only 1 piston. The entire caliper slides back and forth on a couple of steel guide bolts. They do this for a number of reasons. The calipers are much less expensive to manufacture. And the lack of a piston on the outboard side allows for better wheel clearance. This is why many multi-piston big brake kits require wheel spacers to create enough room behind the spokes for the additional caliper width.

4-piston, 6-piston, and even 8-piston calipers are designed to allow the use of wider pads. Single piston floating and 2-piston opposed calipers usually are loaded with pads that are almost square in cross section. For example, here's the pad shape used in the StopTech ST22 caliper (and Nissan 350Z Track Model with Brembo calipers):

Compare this to the wider pad used in the ST60 6-piston caliper:

You can see that a single piston would not work on the wider pad.
Dave Zeckhausen
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