What this calculation does is average the diameter of the rotor and the diameter of the rotor minus the piston diameter. Doing that finds you the center of the piston. That is going to be pretty close to the center of the pad.
I know this is an old thread, but I kind of tripped over it just now and just have to ask a question.
The calculation of the effective radius of the rotor completely confused me. So I read through the thread and found this post explaining what the calculation is supposed to do.
My question is, if the calculation is supposed to average the diameter of the rotor and the diameter of the rotor minus the piston diameter,
shouldn't the piston diameter be doubled? A larger diameter minus a smaller diameter doesn't return the inner diameter, it returns the diameter of the circle that would pass through the smaller circle. On the other hand, a larger diameter minus a smaller diameter divided by 2 would return the number I believe you are looking for.
Another way to calculate it is half the diameter of the rotor, minus half the diameter of the piston.
For example, a 11.75" rotor has a radius of 5.875", and if you laid a 2.75" piston on the edge of the rotor and came back in to the center of the piston 1.375", the radius from the center of the rotor to the center of the piston would be 4.5". The calculation as it stands returns 5.1875" which is only .6875" less than the radius of the rotor.
Am I missing something? Is that not what you are shooting for, the distance from the center of the caliper piston to the center of the rotor?
Not trying to start a fight, or nit pick anything, just trying to understand the math.
