Optimum Brake Arm Angle

[Kieran Enright.]

Years ago I read in a book that, for maximum efficiency, when a brake is pulled hard on, the included angle between the operating arm (on the drum) and the cable should be just less than 90 degrees, as the theoretical maximum efficiency is at exactly 90 degrees. It went on to say that once the included angle exceeded 90 degrees, even by just a degree or two, the efficiency dropped off enormously. Having carried out a few experiments on bikes of my own, I can vouch for the truth of the above, but I still don't know why. At a guess, it might be something to do with a triangle of forces drawn up from the vectors, and maybe you could prove it with maths or trigonometry, but can anyone explain it in plain English?

Kes Enright 13090

[clive]

no idea of the physics of it but I can also confirm from experience that it is true.