A question about seattube angles, seatpost setback and riders with short legs/long(ish) torsos.
For riders with short legs and long torsos (like me: 5’9"; inseam of about 30; 155 lbs; fairly flexible), what do you think about road frames with slightly steeper seat tube angle (ie 73.5-74) and/or the use of seatposts with zero setback (ie Thomson)?
It’s fall, so I’m playing around with my road bike fit. Currently, I’m riding an aluminum Merckx (sloping geometry, 48 cm, with 73 deg STA, 55 tt, 120 stem at 84 deg, no spacers) with a Thomson post with the saddle all the way back.
What effect would switching the post out for one with about 2 cm of setback have on the fit?
Thanks a lot.
I think the rule of thumb here is that with or with out a set back post you need to keep your knee/ball of the foot and pedal spindle line the same. If you put the set back post on it I don’t think you will change your position on the bike, unless you feel like you need to lengthen your saddle to handle bar distance? But on a road bike fit you still need to keep the knee foot over the pedal spindle the same.
Dan…
Saddle fore-aft and cleat position fore-aft directly affect your knee position over pedal / pedal spindle … therefore 2cm of setback makes a big differrence if you keep the saddle set all the way back … if you change the post and keep the saddle the same relative to BB & pedal spindle AND keep the same relative TT length it does not make a difference.
Your physical / flexibility make up is almost identical to mine and i am riding a Javelin Sebino w/ 73 deg. STA, 55cm TT, 110 stem, w/ Thompson zero -setback w/ seat sitting on center of rails. (i have relatively short femurs, pretty strong trunk, and slightly forward for me creates better leverage) I have no doubts i am better here than i was sitting 2-3 cm further in the rear.
Listen your body and see where it wants to move on the saddle when you need power (forward? - back?) what feels most powerful? efficient? economical? OR … rather than spending time too much time tinkering with it, go to good, professional fitter who addresses these issues 
Goos luck …