A few comments to all. Everyone should understand that the term inseam refers to cycling inseam, not pants inseam. Pants inseam has no place in a cycling discussion. Cycling inseam is measured from floor to firm crotch contact, in bare feet. Pants inseam should always be considerably less.
The two formulas agree almost perfectly. Cycling dimensions should be in centimeters. For example, I have an 83cm cycling inseam. My saddle height is 73cm. 83cm x .883 = 73.3cm. 1.09 x 83cm = 90.5cm. Subtract 17.25cm for my crank arm length and you get a nearly identical 73.2cm.
Both formulas work, as long as you pedal with a significant heel rise, at the bottom of the stroke. To ballpark my saddle height, I set the saddle so my leg is fully extended, with my foot horizontal, at the bottom of the stroke. From there, it only takes a 2-3cm rise of the heel to create the recommended 30 degree bend at the knee.
Last edited by DaveSSS; 02-11-12 at 01:17 PM.