Originally posted by Aztec
Why would you NOT get a tri/TT-specific ride if you already have a road bike? If you do tri events for real (as in you are about your results), then definitely go w/ tri geometry. You absolutely cannot make a 73d seat tube work for the aero position. What you'd end up doing is jamming the seat all the way forward -- and you can find a seatpost without offset to make it move even farther forward giving you a steeper effective seat tube angle. That part sorta works, and gets you to maybe 75 or even 76 degrees. Most tri seat tubes are closer to 78 degrees though. Your next battle is to get the aero bars low enough. Usually, you can't do this on a road bike because the head tube is too high up, so you aren't down low enough to get much aero benefit.
You can think of the aero position as the road position, just rotated forward from your feet. Your leg/hip angle should be the same as your road position. But that's almost impossible on a road bike, and instead you just end up with a tighter leg/hip angle and/or bars too high.
Check out timetrial.com. It's Cervelo's site. They do some explaining of this stuff. I'd consider their bikes, as well as see if Colnago makes a time trial or tri-geometry frame (I think they do). The upside from the Cervelo is that you'd have a WHOLE BIKE for the price of just the Colnago frame...
