Originally Posted by Jandro

All fixed gear bikes have just as much breaking potential in the rear as a geared bike. They just use their legs, rather than calipers. You can lock up the rear just as easily with either. Front breaks are what you should be worried about as they make up 70% of any bicycle's breaking potential. As long as the rider is competent and has a front break, s/he can ride with me - regardless of drive-train.