Originally Posted by
Noonievut
I measure setback by placing my bike in the corner of a room, measuring from the wall where the rear tire is touching to the BB, and then to the saddle (same saddle each bike), I'm less concerned with the actual setback # for a bike, then the difference between them (with one bike feeling spot-on).
OK, sorry that's not going to work without a lot of extra maths taking tire sizes and chainstay lengths and more into account.
The way that you should measure saddle setback is from the centre of the Bottom Bracket (BB) and you measure it to the tip of the saddle.
Place a rule/measure from the tip of the saddle and forwards towards the head tube. Drop a plumb line down to intersect with the centre of the BB axle and measure the distance on the scale. As a comparison this works best if you have the same saddle on both bikes.
Anyway, the true zero, zero point for all fit measurements on a bicycle (and probably some others as well) is the centre of the BB.