Originally Posted by roadgator
in addition to the geometry issues, they are more areo-dynamic since they are smaller. triathlons arent governed by the UCI which mandates 700c front and back on all bikes, otherwise TT bikes would have them too.
not quite. UCI does not mandate a specific wheel size. They actually give a range of allowable wheel diameters (55-70cm incluing tires, I think)
650c fits into this range.
The only requirement would be that both wheels be the same size.