Right now I’m riding a 52.5cm toptube/100mm stem on a 78 degree STA bike with 105mm head tube. If I change to a bike that has a 74 degree STA and 54cm toptube with 110 head tube, how much true difference are we talking? Is it just 1.5cm longer or does the STA come into play?
Is there hard rule that increasing the STA 1 degree= Xcm off the toptube?
Thanks.
Using the custom geometry calc on the top of the page and entering the stock numbers from the manufacturers site, I came up with the 78 deg/52.5cm TT an effective TT of 52.42cm
the 74 deg/54cm TT was an effective TT of 54.15.
So it seems(if I did it right) like they will be close to the advertised dimensions.
Decisions, decisions.
Depends. Are you measuring true top tube? i.e. the length from where the seattube and top tube meet to where the headtube and top tube meet or are you measuring saddle setback. Your body cares where the seat is. Measure the length from the contact points and the geometry to get there becomes pretty much irrelevant in terms of fit.
I’m seeing what it would take to get an identical position, i.e. 2cm shorter stem.
I should add that I rarely race tris anymore, and have some UCI ruled events, so I need to be able keep the bike within those specs. That’s why I was wondering, right now my bike is only illegal in the fact that my saddle tip is like 1cm too far forward, something that would be easily corrected if needed be. I just didn’t want to get a new bike and realize that I have to push the saddle 2cm farther forward, resulting in needing to move it back 3cm+ to make it UCI legal(in which 3cm back is a sizeable movement IMO).
Thanks.