Originally Posted by
gugie
When I took the UBI framebuilding class in 2016, one of my classmates was building a polo bike frame. A very short wheelbase and upright seat tube were part of his design.
Modern triathlon bikes are built with more upright seat tubes to move the saddle further forward in relationship to the bottom bracket. This changes how the muscle groups are used so that it's easier on the body for the bike to run transition. @
SwimmerMike might have more clarity on that.
With such a short top tube, this isn't a triathlon bike, most likely designed for bike polo.
Since you asked on the Triathlon set-up:
There's two reasons for the steep seat tube.
1) For better aerodynamics, you need to rotate more forward, the more you rotate, the better the aero position (to a point).
2) For running off the bike, the more forward position is supposed to save your hamstrings.
Back in the old days (early 90's when I started triathlons) the target was a 78-80 degree seat tube which effectively rotated you 4-7 degrees (Plus I end up "nose sitting") for even more rotation forward. I had a "forward" seat post that allowed me to move the seat about 3 inches forward of my road set-up and just swapped in the seat and post for "Aero work" and swapped it back for group rides or climbing.
The picture of me setting up my Triathlon-bike shows the forward rotation, if you picture a normal set up and rotated the picture it would the equivalent of me me riding on the drops. There's no way I could race for 56 miles on a 73-74 degree seat tube road bike in this aero of a position. I feel get at least 2 MPH of speed if I'm "on the bars".
Yeah, the position is supposed to help the hamstrings, I haven't personally picked up on this. I'm sure it's real, but I don't have any problems running off the bike from either type of bike.
Mike