Whats the difference
1, Whats the difference between the tri, times trials and road bike
2, How do you measure frames sizes as my old steel 531 framed Joe Waugh road bike is a perfect 21.5 size for me
Geometry, all three activities use slightly different muscle groups so the geometry reflects that; the angle of the the seat tube is typically 73-74deg from horizontal to 76deg TT, 78deg+ for Tri. TT/tri bikes have shorter top tube as you need to get into an aerodynamic tuck.
This may be of use for sizing
tri bikes are where you will end up. Buy a road bike and regret it... buy a TT and love it like your new baby. In fact go sell your house and buy the best TT you can...