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Old 02-26-06, 06:35 PM
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AnthonyG
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Originally Posted by jp_nyc
Thanks for the info, that's really helpful. The 'cross frame has a slightly compact geometry (whereas the road frame doesn't), so the effective top tube measurement will be shorter than 51.5cm (actual length from seatpost joint to headtube joint). If the seat tube angle is more relaxed than the road, that means the saddle is further behind the BB, correct? That might be something to think about. Since I want to build a fixed gear with it, I'll want to have a more forward position.

How much of a difference in position (relative to the bb) is there between a 72 and a 74.5 degree seat tube angle?

You've got the concept. I'm using the term "effective top tube length" pretty loosly. If you set your seat up to have exactly the same seat setback and height on both frames then effectively the top tube wouldn't be so long on the cross as the seat would be set much further back on the road bike to acheive the same seat setback which therefore EXTENDS its effective top tube length. From what i've read 1º of seat tube angle is about 1 cm of top tube length difference. Before you think that you NEED a more forward riding position than the cross bike provides maybe you should measure your KOPS position on your current bike. I suspect that you are infront of KOPS and the more rearward seating position on the cross bike may be just what you need. You could always use a zero setback seatpost if required anyway.

Regards, Anthony
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