Instructions
Position your bike with a 100 meter run up to the jump.
Press and hold the R1 button on a PS3 or the RB button on an Xbox.
Push the Analog stick on your controller quickly upward as soon as your front wheel hits the bottom of the ramp.
Push the Analog stick on your controller quickly downward as soon as your front wheel hits the top of the ramp.
Let go of all of the buttons when your bike is exactly halfway through the backflip.