Originally Posted by ThermionicScott

^ For what it's worth, that calculator is built from the Frank Berto charts referenced above. My suggestion would be not to use the 40%/60% setting unless you ride an upright bike in a flat city. 45%/55% puts a bit more of the air in front to avoid pinch flats and wallowing, and your butt may appreciate having only 89 psi in the back.