Your Truck is dead and has no brakes, just focus on steering. Just knock the car off the edge without falling. The way to earn this achievement is by completing the Campaign Mission: "A Rocky Start" If you fail restart a level and try again You don't need a perfect score on any of level's, just a passing one If you are having touble with corners, let off the gas and it will be a little easier to turn while your not accelerating. Go as fast as you can and hit the wall as centered as you can. Too fast and you may over shoot, too slow and you will under shoot. I hit it going about 60mph off the ramp.
This one may take a few tries so you may need to restart the mission You dont have to make it to far to pass. After you start moving down hill use the brake / hand brake to slow and steer yourself. Dont hit the rocks fast or you may blowout a tire or damage the bumper. Tap the aim up button quicky 1-2 times to hit the car. Dont speed on to the rocks you can blowout a tire. Hit the car near the edge as center as you can and as fast as you can for a good score. A slower speed makes it a little easier to center yourself Try your best to stay centered, you only need to get about halfway for a decent score. Your opponent will catch fire and crash, so get in front of him before or wait until they crash and dodge the debris after. Get as much speed as you can and race at an edge(farthest edge will let you build the most speed) The way to earn this achievement is by completing the Campaign Mission: "Senseless Destruction"