My first suggestion would be to make sure that V-Sync is enabled. Playing this game without V-Sync (or maybe just if your frame rate is too high) can cause problems with how some objects in the game interact. The most common one seems to be problems controlling the RC car, but it can cause other problems, like not being able to make a simple jump.

Video card drivers can override the V-Sync setting in the game, so you can have Steam, or something else, display the frame rate while you're playing, to make sure that it matches the rate set in the game.