Originally Posted by ultraman6970
with the cycling shoes on, measure your crotch starting obviously from the floor. Take the number u get an multiplied them by 1.90 or by 1.887 depends from you, then u are all set. The number u get should be the lenght from the center of the BB up to the top of the seat, Please follow the seat tube line ok?
I agree with ninja man, but always use the cicling shoes...
the other methods work also, always u can try the other methods and compare with the formula ones
I like this method, without the cycling shoes, but Ultra's numbers are wrong. You multiply the inseam by 1.09 (NOT 1.90!) to get the distance from the axis of the pedal to the saddle top at the middle of the saddle. It this case the crank arms are aligned with the seat tube.
OR, you multiply the inseam by 0.887 (NOT 1.887!!) to get the distance from the BB center to the saddle top as above.
For 170 mm cranks the two calcs are really really close, but for other crank lengths there may be slight differences.
You also need to get the saddle fore/aft position where you need it. The classic starting point here is to get good sit-bone support when your knee is over the pedal spindle when the pedal is at the 3:00 position. Google KOPS for more info on this. It's only a starting point, but it is a standard starting point. You may want to adjust back and forth between saddle height and saddle fore/aft and saddle angle (classically it's level) to get all three right at the same time. Depends on how particular you are.
Then as you ride, see if the saddle pressure is good (on the sitbones and not on the boys), your hips are not rocking and causing abrasion, you don't have pain in front of your knees (saddle too low) or behind your knees (saddle too high). If you can ever get all these things right for a 100 mile ride, I think you're home. I'm not home yet!
Note that touching the ground with your feet does not enter into the picture. Presumably after you've ridden enough to get this far, you can stop without falling over.
The most critical part, though is saddle height, and most people have it way too low.