Motionsports

Try this on the Intermediate or Advanced Courses. You will have more jumps in which to tackle this achievement without those long reload times.

To make a perfect jump you need good speed and should rise in the saddle as your rider hits the middle of the arrow in the white area indicating a jump is looming. Timing is key, an absolute perfect approach angle is not.

If you do this in 4 player, it'll cut the loading time down by quite a bit, saves going back to the main menu as much when you die and it will still save your progress.