[200q20v] Re: Brake clamping forces

GSTREIN at aol.com GSTREIN at aol.com
Wed Jul 4 13:08:48 EDT 2001

This topic is being confused by physics.  The clamping forces may be the same 
yet the impact the force has on the pad size (dimensions) may be quite 
different when more pistons are present.  An evenly applied force which 
covers more area of the brake backing plate will hold the brake pad against 
the surface of the rotor with very little distortion to the pad and thus 
greater contact area - leading to greater friction and more dependable 
stopping power.  Consistent brake pad contact surface area is what counts 
when racing.

The high performance market has very good reasons for more pistons and 
monoblock caliper designs.  At high speeds it takes very little time to bring 
the brake rotors/pads surfaces up to a extreemly high temperatures (you will 
see the rotors/pads literally glowing).  When the brakes are applied in these 
conditions the pad, caliper and rotor will all tend to distort.  Using thick 
rotors and rigid calipers (monoblock being more rigid than most 2 piece 
units) you reduce this distortion/warpage.  The more pistons the caliper has 
will keep the pads pressed evenly from edge to edge (less distortion than one 
with fewer pistons) and thus will be less likely to distort as much and more 
likely to give more contact area and more friction.

Even with the UFO large piston if you were to race this application you would 
more than likely upgrade to a multi-piston setup.  The large piston works 
fine for daily or even moderate brake use but if you were to measure the 
contact pressure at the ends (leading and trailing edges) of the pads you 
would see that it would not be less than the center which is directly under 
the large piston.  As the temps and distortion increase the pad contact will 
continue to be reduced. In addition, the gases taking the least path of 
resistance out from under the pad will "float" the pad off the rotor surface 
in the areas of least contact pressure or the areas of greatest distortion.  
If you replaced these UFO Calipers with performance multi-piston units that 
covered the pad backing plate more completely you have better braking 
performance due to less distortion and more consistent contact of the pad to 
the rotor surface.

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