Game could utilize some mechanics.
Make a rollover a gameover (make a trigger on the roof, if it touches the ground - you're done)
Grip upgrade does nothing, I think it can counteract slipping from slopes. Right now car is just a spidercar. You can climb what your speed allows you - that's not interesting.
Map is pretty, but it's simple. Settle some trees, they will not only decorate the scene but also play as an obstacle.
And there's no obvious way. You yourself can be smart but average web-gamer shouldn't.
And please decorate game a bit. Place flags to mark the route, give huge-ass timer to compete, provide fancy skins for the car (which itself is modelled pretty good, not only for a prototype) - and we're all yours.