Frame sizes??

[graff71884]

I need a little help. I am looking to buy or build, haven't decided yet, a cyclocross bike but haven't figured out exactly what size frame I will need. I ride a 06' Trek 2100 road bike in a 56cm and don't know what that translates to in a cyclocross bike. I am about a 32" inseam if that can help me chose a frame size. I have looked at a Trek that was a 56cm and it fit pretty good, but I was wondering if anyone could help me decide on a sizes for Fuji, Cannondale, and Kona. I found good deal on a Fuji, but need to find out what size I would need because I won't be able to get on it before I buy it. Thanks for any help in advance!

[cyclintom]

You will discover that the differences between REAL road bikes and REAL cyclocross bikes aren't readily quantifiable.

Two measurements which will make more sense to you are probably:

A cyclocross bike should have between 1 1/2" and 2 1/2" of clearance on standover height. It should have about 1-2" less top tube length.

You will find that seattube length doesn't relate very well to cyclocross bike size much as mountain bikes have completely different sizing philosophies.

This might help some:

http://www.bikeforums.net/showthread.php?t=138316