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Old 12-04-07, 04:04 PM   #1
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What's the effective top tube?

I'm looking at this bike with the following specs: 57 cm center to top; 72 seat tube angle; 72.5 head tube angle and a 57 cm top tube. I'm trying to figure out what would be the effective top tube with the bike properly adjusted. Assume a 76.5 cm saddle height and bars 2cm higher then the saddle. Can this be figured out w/o a measuring tape?
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Old 12-04-07, 04:05 PM   #2
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The frame size is actually 58 cm center to top.
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Old 12-04-07, 05:04 PM   #3
Time for a change.
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Why get technical. Measurements don't work because of so many factors. If it has a 58cm top tube- then it has a 58 cm top tube. By raising the saddle and bars by 2 or 4 cms- you can then adjust the seat or bar stem length to suit. You could be putting the seat as much as 7 cms further back- or further forward, and the same on the length of bar stem you fit. That can alter by 10cms if you wish it to.

So in reply to your question the only way -Unless you know where the saddle and bars are going to finish up in the fore and aft position- is to set the bike up and measure- but the top tube will still be 58cms.

Unless you get onto the bike guru on this forum and he disagrees- But I am certain that DG will come up with the same reply.
How long was I in the army? Five foot seven.

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Old 12-04-07, 05:09 PM   #4
just keep riding
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Effective top tube does not vary with saddle or handlebar height. On a bike with a level top tube (the way nature intended them to be), the effective top tube length is the top tube length. If the top tube slopes to the rear, the effective top tube length is the level measurement from the center of the head tube to the center of the seat post at the point where the top tube should intersect the seat tube.
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Old 12-04-07, 05:12 PM   #5
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Effective top tube length is a way of comparing sloping top tube bikes to the traditional horizontal top tube. Bike setup has little to do with it.

Measure from the centerline of the head tube in a horizontal direction to the centerline of the seat tube as if the seat tube extended up that far and that is the length of the virtual top tube.
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