The key here is to simply drive slowly and carefully, using the left analog stick to balance your car so that you don't take damage. Boost only when you need to (e.g., gaps). Forget about the game telling you to do somersaults, it's just not worth the risk. The last stage is obviously the hardest due to the large number of rough edges, but almost every rough/ high edge could be overcame simply by holding A long enough. For those that you couldn't, tilt the left analog stick backwards and then try again. I'm not an expert in this either, but I managed 3.8K+, 3.8K+ and 2.5K+ to get the 10K without much problems.
I had more problems with the balloon and boat, because you actually had to do 10K on them, and it gets faster later in the run. I'm just glad these bloody races are out of the way!
Last edited by neeker75; 10-23-2009 at 05:59 AM.