You need to grab one of the three (initial at least) trucks in the game, by going to the Autoshow, hitting
and then selecting the "Truck" type, which is the last one on the list.
Buy either the Volvo or the Mercedes, those are actually meant to be raced and auto upgrade them to the maximum possible PI. Then, while having Rewind set to "on" so you don't have to climb hills each time if you fail, go towards the Ambleside Edge Danger Sign, which is just to the west of the Festival hub. If you set a waypoint to it from the Festival itself, you can actually get a pretty good run towards the jump, down a pretty fast right-hander. Get out of the corner, focus on getting that speed up and line up the jump.
As soon as you successfully land it, the achievement will pop, regardless of whether you've completed the jump before.