Pretty much aerodynamics.. If you put yourself inside a fully streamlined Velomobile,
it doesn't matter how wide you are, but if your body is out in the wind and the air has to be pushed aside
by a less than smooth low drag shape,
then the high end pro race kit will just make you feel fast..

but the kid, Sam Whittingham, in the Varna, a 2 wheel human rocket, would not be clocking 80mph, on the desert flats,
on his conventional Road bikes, either.