The secret to bumper cars is patience. Do Not, I repeat, Do Not jump into a 3 car pile up. While this might be fun, you will without a doubt take more damage than you give! Single one car out and ram him at full speed. Speaking of which all collisions should be at full speed. This will ensure you do the most damage and take the least punishment.
Don't be afraid to run away. By the time they catch you, you will be at top speed and it will hurt them more than you anyway.
Stay away from walls they are nuthin ba trubble.
Hit and run. "Those who fight and run away, live to fight another day." If you hang around he will hit you back and you won't be happy. Remember it is better to get 75 points per round and last 7 rounds than 100 points a round and die on level 2.
Almost always grab the items that pop up. A new one won't appear until you do. If it is an oil can, then make someone else run into it. If you can't trick/force someone else to get it you might have to take one for the cause. A wrench won't appear if there is still an oil can there. If a wrench appears in the middle of the arena get it so that they can't, but if it is near the wall wait until you need it. The CPU cars will not go for it.
Never under any circumstances hit a mine. If you have to choose between a 3 car pile up and a mine, then go for the cars. Be careful though, there is nothing worse than picking the cars in that situation and then having one of them drive you into the mine.