Easy achievement, even more so if you have played reflex. The trick list is the same for this game as the one for reflex. Basically, approach a ramp with a decent amount of speed. before you hit the ramp/jump hold down either LB or RB depending on your control set up (RB is the default).whilst holding the bumper push the right stick down (again this will depend on your set up. if you change the controls to Lefty you will need to use the left stick). So as you are going up the ramp you are pushing the stick down whilst holding the appropriate bumper, this will cause you to perform a backflip. whilst in the air holding the accelerator will speed up your flip and the brakes will slow it down. Should take no more than 3 attempts to land one backflip (or 3 in one jump if your awesome!)