Originally Posted by
AnthonyG
Modern bikes with 700c wheels only "Work" down to medium sized. The "Small" or 48cm, 50cm or even 52cm is always a fudge.
Nominally, when you reduce the top tube length or more accurately the reach you are talking about pulling the front wheel closer to the bottom bracket. You can only do this properly down to 54cm sized bikes. Bellow 54cm they fudge things by steepening the seat tube angle which makes the top tube length shorter on paper but in reality short people need the handlebars pulled back, not the seat pushed forwards. In smaller sizes they also slacken the head tube angle which pushes the front wheel out while shortening the top tube length on paper.
This small frame we are discussing is just the medium frame which has been fiddled. If you really want to do a small frame properly you need smaller wheels along with shorter cranks which is another discussion.
Anthony
Well see, that's what's confusing me. I have three 9 or 10-speed 700c frames with horizontal top tubes: a 50cm with a 51.5cm top tube, a 52cm with a 53cm top tube, and a 54cm with a 54cm top tube. I have fitted all these bikes so that my position is very similar between them. I'm a little more upright on the 54 because the headtube is longer and also more upright on the 50 because I'm a little bit scrunched. On the 50, I also can't really get my saddle back far enough because the seat tube is steeper like you say, and the head tube slacker. The 52 is really my size and I'm lowest and most stretched out on it. I've ridden them all on at least century rides with no problem. I'm a short-legged 5'6.5".
All that said, the TT lengths do vary by ST lengths and thus it could be expected that normal length stems would work well enough for riders of the appropriate size for each of these frame sizes, though the balance of each bike might be slightly different.
The OP may have slightly shorter legs than average for his height and thus a longer torso, which is also my case. Thus I like a bike with a longer top tube and enjoy bikes which are larger than might be usually recommended to me. These have the added benefit of getting the saddle further back and thus better able to balance my long torso. The downside is that my hip angle is more closed and I really can't be fat and ride well. Or maybe that's an upside.