Originally Posted by
Road Fan
Ok, so the OP said his inseam measured with help is 35.5”. To get the frame size, multiply by 0.665 to get a frame size of 23.6,” rounding up to 24”. So the nominal frame size is 24.” To get the saddle height, BB center to top of saddle for 170 mm cranks, multiply 35.5” by 0.889 to get 31.56 from BB to saddle top. Lower the saddle by 0.1” to account for the longer 172.5 mm crank arms. So your Lemond-Guimard frame size is 24” and the saddle height from the BB center is 31.46.” From the pedal axis it’s 38.23” saddle height.
I think I got all the Guimard factors right, but these are, like KOPS, only starting points. I’ll leave the rounding up or down to you guys. 5’10” tall? I’m 5’5.5” tall, and I like my bikes 52 to 55 cm, depending on the rest of the geometry.
If the OP’s cycling inseam really is 36”, I’d say 24” is still the suggested frame size, and the saddle height goes up to about 38.6” above the pedal axis.
I also use heel on pedal as a saddle height starting point, wearing the shoes and shorts I usually ride in. I usually have to adjust from there, down a bit.
The only caveats I would add would be to do this all in CMs assuming the bikes are sized in CM. When I convert a 36" inseam to CM and do the math, I get a 60.8 CM frame measured C to C. And, be careful with measuring saddle height from center of BB because it won't work if you have bikes with different crank arm lengths. As I said this always gets me in the ballpark. From there it's a matter of adjustments. I'm just sharing what has worked for me.