Pretty fun game!
Some suggestions:
Instead of showing "Car4", show "Player" or if you eventually add the ability to enter the name then show the name.
More tracks.
Allow the player to select the number of laps.
Make crashing end your run. Although I do like the strategy of having the computer guys ram in to you to slow them down.
Maybe adding more obstacles even in the middle of the track.
Branching paths / shortcuts
Maybe having the grass start to ruin your tires.