Why don't frame sizes (seat tube length) use "effective" sizing?
12-08-14, 01:02 AM
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Why don't frame sizes (seat tube length) use "effective" sizing?
Seems to be a pretty large range of sizes at any given seat tube length, with compact frames and seat tubes that rise well above the top tube. It was probably pretty straight forward back when all bikes had perfectly horizontal top tubes.
How hard would it be to use some type of "effective" sizing? Project the top tube as horizontal and always measure from the center of the bottom bracket to the center of the imaginary top tube.
How hard would it be to use some type of "effective" sizing? Project the top tube as horizontal and always measure from the center of the bottom bracket to the center of the imaginary top tube.
12-08-14, 01:11 AM
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What purpose does knowing seat tube length serve?
Effective Top Tube, Stack and Reach are all you really need to pay attention to unless you're in jepardy of running out of seatpost adjust in either direction. Seat tube length is, So Last Century. :-)
Effective Top Tube, Stack and Reach are all you really need to pay attention to unless you're in jepardy of running out of seatpost adjust in either direction. Seat tube length is, So Last Century. :-)
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12-08-14, 01:14 AM
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But it is (was) always the starting point. Standover height can also be important, and is more closely related to seat tube height.
12-08-14, 03:07 PM
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Once you know the standover height & stack then seatube length becomes largely irrelevant, unless you have a very specific frame geometry in mind.
Last edited by yankeefan; 12-08-14 at 04:41 PM.
12-08-14, 06:28 PM
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Seems to be a pretty large range of sizes at any given seat tube length, with compact frames and seat tubes that rise well above the top tube. It was probably pretty straight forward back when all bikes had perfectly horizontal top tubes.
How hard would it be to use some type of "effective" sizing? Project the top tube as horizontal and always measure from the center of the bottom bracket to the center of the imaginary top tube.
How hard would it be to use some type of "effective" sizing? Project the top tube as horizontal and always measure from the center of the bottom bracket to the center of the imaginary top tube.
You'll see that there is an "effective top tube" length that emulates a horizontal top tube, and that it is in the ballpark of the frame size. At the extreme sizes it is farther off, but that was normal in the days of horizontal top tube steel frames, too.
Note also that the nominal frame size is bigger than the actual seat tube length, reflecting the sloping top tube. So "effective" sizing does exist, and at least some manufacturers wanted to provide continuity for customers who still remember shopping for bikes by seat tube length.
- Scott
