from experience my

R20 with 451 wheels works great the larger wheel diameter adds crank/pedal clearance compared to 406 w/c is more likely to hit ground ridden fixed

I flip flop to Single speed for now ...haven't got used to Fixed riding style yet

stripped and upgraded this one is down to 10.5kg or 21 or so lbs. or less if i remove rear barkes/shfters/metal clamps/etc.

It was a 36lb. monster when i got it.