I'm not following your math or your reasoning. FWIW I am 5'10 and my inseam is around 33". I have 165mm pedals on one of my bikes. Most of them have 170 but a couple have 175. None have 172.5. If you get from that that I don't think that there is a magic crank length for a given inseam you would be right. Nor do I think the average person could tell the difference between a 170 and a 175 crank. But lets say it is true. How does the 2.5mm difference in crank length result in a 25mm reduction in seat height?

H