Buying a cheap road bike online, basically just for computrainer use. I ride a 60 cm Trek Hilo 2000 tri bike, can I be relatively certain that I would ride a 60 cm road bike???
top tube for the road bike will probably be longer
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So maybe I would be better off erring on the side of smaller like a 58cm??
Like the previous poster said, the top tube should probably be longer, assuming you have a normal size stem. I think it says on this website that a tri bike should have a 1-2cm shorter top tube. As far as frame size goes, I would check out some of the formulas given for frame size based on seat height, then I would check a given bikes geometry to make sure the reach is going to be okay based on my current tri bike top tube plus 1-2 cm.