"Ivan Vegvary" wrote in message
news:RVcDf.7671$Cf7.7003@trnddc06...
Watching "Classic Car Restoration" the host made the statement that the
brake caliper on the restoration car (1969 Alfa Romeo) had twice the force
on the rotor (compared to single piston calipers) because it has a dual
opposing pistons, one pushing on each of the brake pads.

Is this a myth, like 2 cars, 50 mph each traveling at each other, creating
an equivalent collision of 100 mph? (In reality it is equivalent to one
50 mph car slamming into an unmovable (50mph reaction) object, e.g.,
concrete wall, 5' diameter oak tree, etc.

For example, if a single piston caliper is able to apply 500lbs. of push,
there would have to be 500lbs. of resistance from the other side of the
caliper frame. Total 1000 lbs. 'squeeze'. All things being equal, if in
a dual piston caliper, with each piston pushing with 500 lbs. force,
doesn't the rotor experience the same amount of friction against turning?

Where is my thinking wrong?

Thanks for replies,
Ivan Vegvary
I think you are forgetting there are two reactions, the force of the rotor
against the near brake pad and the force of the other side of the rotor
against the brake pad on the other side, translated through the frame of the
caliper. In this case it is the rotor that supplies the equal and opposite
force. The force of a single piston would be distributed on both sides of
the rotor, assuming no friction on the sliding mechanism. A second piston of
the same size would double the "squeezing force", however the fallacy in the
commentator's statement lies in the fact that the dual piston design would
use correspondingly smaller pistons. The reason for the design is to make
sure force is equal on both sides without relying on the sliding frame, not
to double the braking force, as another poster pointed out.