Why is the frame size often longer than the seat tube?
05-26-06, 10:31 AM
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Why is the frame size often longer than the seat tube?
Why do some bike makers size a frame with a number that is higher than the actual seat post length? For example, a 57cm Bianchi Eros's seat tube is only 54cm long.
05-26-06, 10:33 AM
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Mainly Compact Geometry. The top tube is sloped so they list the frame size as if the seat tube made the top tube parallel to the ground. Make sense?
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The road don't go nowhere, stays right where it is.
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05-26-06, 10:44 AM
#3
Who is Austin Dunbar?
Compact geometry
With a compact frame, the actual seat tube length becomes irrelevant. The measurement they are giving you is a "virtual" frame size. It is what the comparable frame size would be if the top tube was level. These days, it is more important to pay attention to seat tube angle, head tube length and the top tube length when looking at frames. Knowing these dimensions will allow you to fit a frame properly whether is is compact or conventionally sized.
Even when all top tubes were level, frame sizing was somewhat ambiguous. Some builders would size center of bottom bracket to center of top tube (c-c) or center of bottom bracket to top of top tube (c-t) and still others were center of BB to top of seat tube (c-meaningless dimension). It is always best to look at top tube length (actual or virtual) and seat tube angle when comparing frames. You also need to consider head tube length in order to insure you can get the bars high enough to be comfortable.
Even when all top tubes were level, frame sizing was somewhat ambiguous. Some builders would size center of bottom bracket to center of top tube (c-c) or center of bottom bracket to top of top tube (c-t) and still others were center of BB to top of seat tube (c-meaningless dimension). It is always best to look at top tube length (actual or virtual) and seat tube angle when comparing frames. You also need to consider head tube length in order to insure you can get the bars high enough to be comfortable.
