Would be cool to have the tires switch to whatever dominant surface the track uses, for sure.
As for tiers of cars, currently the idea is to have something like 4 tiers: speedster, racer, dominator, tank (names are just examples)
Speedster - quickest acceleration, low top speed, responsive steering, low weight (easily thrown around by missiles, mines, etc)
Racer - fast accel, medium top speed, good steering, average weight
Dominator - decent accel, fast top speed, harder to steer, pretty heavy
Tank - slow accel, high top speed, turns like a brick, heavy as f**k and really hard to stop (joking about the brick part)
These are the default cars, but can be upgraded to increase performance. How those upgrades work and how they affect the game outside of arcade mode, is something we're still talking about, but I'd rather not disclose everything we're doing.
And of course, nothing is final yet, so discuss till your fingers bleed