Fun game!
I like how you incorporated the theme. I disagree with the other comments that there is no pressure to increase in size. The game's goal is to get a high score, you even tell us that when we first open the game. The large cars hand brake drifting is much more effective than the small car, and the large vehicle size handles speed bumps much better.
I found the delay when you press gas and reverse a little frustrating at times, but once I figured it out it got a little easier :)