Originally Posted by
merlinextraligh
^ the 74 degree seat angle is going to facilitate a UCI legal set up. The 77 degree is going to open up your hip angle a bit, facilitating the run transition.
A lot of folks run the 78-degree STA in UCI events, but force their bike into the rules by chopping the nose off the saddle and/or riding waaaaay forward on the nose.
Here's Zabriskie, with his old P3 set up in the 78-degree configuration, AND riding on the nose:
For all practical purposes there is no difference between TT and Tri bikes. There are some differences in setup depending on the length of the event in Tri, but the bikes are ultimately the same.
And if you're a regular old USAC cat racer, the UCI rules don't apply to you anyway.