The problem is that it will become a bit too arcadey if you understand what I mean. Do you know the game Slipstream? It also have a drifting mechanism, but controlling the car is so vague that it becomes frustrating to me.
If I'm about to implement drifting, I want it to feel natural and predictable to me. I've been thinking about how I can achieve this all day, and I think I have an idea, but it's going to be a lot of work.
At this moment you've unlocked the only two vehicles, but there's a 3rd on the way: the Corvette ZR-1 that you race against with the bike.
And I guess I have to make more stages!
Oh, have you tried the manual transmission?