Correction

Correction

In the "Tech Tips" section of the November Service column, I unintentionally supplied the wrong data regarding the amount of braking force present in a brake caliper with opposed pistons. I stated that if the pressure generated in the braking system at the master cylinder were 50 psi, and if the caliper had two pairs of opposed pistons, with each caliper piston having three times the area of the master-cylinder piston, the total braking force would be 600 pounds (50 × 3 × 4=600). That is incorrect. For a caliper in which the pistons are opposed, the combined braking force is only equal to that provided by the pistons on one side or the other. If one set of pistons in the same braking system is pushing in one direction with a given force, the other set can only push back with equal force. So in this instance, the combined braking force would be 300 pounds (50 × 3 × 2 =300). The pressure exerted on one side of the rotor would be 300 psi, so naturally, it would also be 300 psi on the other side. If all four of the pistons were on the same side of the caliper, the combined pressure would be 600 pounds, but not if they are opposed.

When writing this particular "Tech Tips" entry, I went through several iterations that involved multiple calipers, calipers with opposed pistons and calipers with pistons only on one side. Somewhere in that process, I forgot to change the math to correspond with the final version. I sincerely apologize for that oversight. -Paul Dean