Mike,
I think the answer depends on your sizing priorities. If you like to have the top tube or reach a certain way, then you want a particular top tube length regardless of setback (shallower ST angle increases setback, because sets the seat lug farther back from the BB). If you need a particular constraint in stand-over height, then you can use a bit longer seat tube with a shallower seat tube angle. Then the TT might get longer in rough proportion.
Personally, I like a 73 or 74 degree seat tube with a 53 or 54 cm frame, because it lets me get my knees a bit behind the KOPS position. I would not lengthen my TT to compensate, because I have a short torso and can only reach out so far with comfort. Perhaps after some more training I'll want to reach out farther.... My two 52 cm frames (Masi GC and a Mondonico) both have 75 degree or so seat tube angles, and I don't really like the pedalling positions. Not ready to give up on the sexy Italians yet, however!
So what is the geometry and sizing of this Glen Erickson, how it it sized, what's on it, and how much do you want for it? It might be up my alley. Plus there are a lot more 52 thru 54 cm sized riders on the list...
Ken (sitting on my email-reading bum?) Freeman Ann Arbor, MI
-----Original Message----- From: classicrendezvous-bounces@bikelist.org [mailto:classicrendezvous-bounces@bikelist.org] On Behalf Of dddd Sent: Monday, December 26, 2005 4:01 PM To: Classic Rendezvous Subject: Re: [CR]Frame sizing and geometry
Figure on adding about 0.8 to 0.9cm (for frames in the 50-60cm range, c-c) to the toptube length for every degree that you slacken the seat tube. This will keep the relationship between the bb and stem quill about the same, and allowing you to use the same stem length if the seat position can also be made the same with whatever range of adjustment is available.
David Snyder
Auburn, CA
> My question is. What is the relationship between seat tube angle and frame
> sizing? If I normally ride 52cm with a 74 degree
> Seat tube angle would a bike with a shallower angle require a larger
> frame?
>
> Just curious. I may be selling this soon anyway to pay for another
> project.
>
> Mike "Couldn't even ride to Krispy Kreme" Wilkinson