Just upgraded from a 35A KT Controller to a Grin Tech Phaserunner and this thing is a beast now. With the current 48v battery I'm get 35mph and ridiculous amounts of torque! :
Kill Yourself 50% Faster With 2x The Power: E.R.T.'s 72v 50Amp 3000W Ext BBSHD Controller | ElectricBike-Blog.com