Thanks for double checking the math.
Yep, I was looking at it in a linear fashion. Even though I realize it is a diapragm and not a piston. If it is non-linear then I will look for the information to be already published. Some one, some where, knows how much assist these things create.
I wonder, with as small of an amount of travel that you typically get at the master cylinder it is non-linear or if it is, is the amount significant. Even with a parabola approach the length to parrellel would not change much considering the amount of movement, the degree of arc we are talking about.
Some else just occured to me. These diapragm, at least you would think, would have to be 'rigid'. They are attached at the center and around the circumference to 'fixed' points. As the point in the center moves the distance from the center to outside radius would increase. I seriously doubt the diapragm stretches. With that in mind, while it may be a diapragm I would think that it made in such a fashion that it behaves like a pistion. Just some random thoughts.
Of course I could test a car and figure it out that way. Sounds to much like work to me.
Rick