The zipp s9 carbon tubular disc rear wheel has an unassuming profile it borrows from the perimeter shape that makes the sub 9 so fast it can actually generate forward lift when paired with their tangente tires but in place of the sub 9s toroidal bulge the super 9 remains flat from its widest point all the way to the hub this relatively simple looking shape results in a wheel thats as fast as the sub 9 but stiffer than any other disc they make