BILL BOSTON CYCLES

Just how important is seat tube length? 

Back in the ‘70’s when I started riding and later when I started building frames, bicycles were sold by seat tube length. It was common to stand over a bicycle to determine the proper fit. If there was a lot of clearance, we would try a larger size. If there was a little clearance, it was probably OK. If I rode a 23 inch road bike, and wanted to get a track frame, I was told to get one ½ or 1 inch smaller and it would be fine. Little attention was paid to the actual frame geometry in making a selection. It turned out that getting a smaller size track bike was good advice if you were going from a road racing bike with a 10 3/4 inch bottom bracket height to a sprint bike with an 11 ¼ inch bottom bracket height as this would still provide about the same top tube height. If on the other hand, you were riding a criterium bike that had a 11 inch bottom bracket height, this may not have been good advice. 

My point here is that the seat tube length is a result of top tube height, bottom bracket height and seat tube angle. Seat tube length should not be used to determine the proper frame size. For additional insight on this continue reading the following information.  

      Things to watch out for!

Things are not always what they seem. Take for instance a bike with a short seat tube. If the bottom bracket height is in a normal range for the type of riding that you plan to do and the crank lengths you will be using, then everything is fine. On the other hand if the bike has a very short seat tube, but a very high bottom bracket and a sloping top tube, it may actually fit like a much larger bike. Don't just look at just one or two dimensions on your bike. Consider all of the dimensions and their total effect on your fit, comfort and efficiency.

Top Tube Height

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Last modified: July 09, 2014