To convert a bike, using 1000watt motor(s) from golden motor. If you chose to put a motor on the frount wheel, probably will need to be strengthened somehow. i made up two backet to go on either side of the front wheel wedged againts the frame and locking the wheel using its flat sides of the axil and held in by bolting it on. I made a similar bracket for the back. i used a 48 volt battery, 20 amp/hour but will handle 50 amp hour output and as they are microcontrolled they will turn off the batter when the voltage gets to high or to low, and probably to much current to.
You will not necessary get more speed from two motors as they only do a certain RPM but it will take off and get you uphill quick, i get around 40 km/hour of course off road! ha ha If you happen to hit public roads just remember 200watt is street legal, be smart! silicon chip magazine have a good article on the same motor.