I have a question concerning the best crank arm length for my current build. I am 5'11" and have a 29" inseam. The bike frame (TT bike) is a medium size (55 cm) and has 650C tires. My current MTB has 175 cm cranks and this seems perfectly fine, but is there perhaps some sort of equation or magic that can be used to calculate the optimum crank arm length for this bike? Or is this best left to trial and error?