Question: I know that frame size is important when selecting a new bike, but how concerned about it should I be? For example, if I think that 59 cm is my best fit, should I not buy a bike that only comes in even sizes? — Keith D.
Coach Fred Matheny Replies: Frame size was more important when all frames were made in the traditional diamond shape. With a horizontal top tube, stand-over height is a prime consideration. Also, when all bikes had quill stems and threaded steerer tubes, the frame’s seat tube had to be long enough for the handlebar to be high enough in relation to the saddle.
So, if you’re getting a diamond-frame bike, frame size is important. That said, one centimeter (about 3/8 inch) larger or smaller than your ideal shouldn’t matter. The difference can be taken up with the seatpost, steerer tube, and stem rise and extension.
With the new breed of frames that have sloping top tubes, seat tube length is all but meaningless. It’s the effective top tube length that’s important. In fact, some makers of these so-called “compact” frames offer only three or four sizes. They fit customers via seatposts and stems.
The best way to make sure you’re getting the ideal frame dimensions is to have a professional fit. Fitting can be done by coaches or bike shops that use a pro system, or by a physical therapist who specializes in working with cyclists.