I’m sure someone can answer this exactly. How far (in centimetres) does each degree of the seat tube angle move the bottom bracket in relation to the confluance of the toptube and downtube? I know this will vary based on seat tube length/saddle, so perhaps there a reference/resource for this, on the WWW I can view?
Thanks.
Check out Dan’s Geometry Experiment articles. I think he answers this pretty well in those write-ups.
Thanks for the link.
It appears (roughly) that one degree equates to one centimetre, even in road geometry? I’m looking at a new road bike with half a centimetre seat post angle difference, and the head angle is the same. So, it appears that (roughly) half a centimetre difference between center of saddle and BB, but my sade should be in same position for a neutral knee position, thus my TT length would need to be half a centimetre longer?
See my confusion!?!?!?!?
Just slide the saddle rails along a bit. Only problem would be if you’re at either limit of the rails already in which case you may need to look at a different seatpost.
Thanks. When I move my saddle forward on the rails, to give my knee the same neutral position in relation to the BB as previous, the TT would shorten (roughly 5mm) due to the slacker geometry. Thus, the TT is effectively 5mm shorter (assuming same TT length), so size frame change, or stem would be required. I think this is correct.
Tell me which bikes you’re looking at and I’ll work out how to match your position. need current bike, stem length and angle + spacer height (incl headset top cap). Just need frame model for new bike
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