hey. ive just been thinking about these things:
tyres-when u burnout bits of tyre fly off or when drifting you can shred the tyres
grass and dirt- when u go off onto the grass your car can get clogged with mud and if people run off in the same areas ,make it so it goes all boggy or worn out or something?
also smoke physics-after a big drift or burnout the smoke stays longer, when doing a burnout the smoke looks like its pouring out like in real life sorta well yeah

thanks

lots of smoke slows the computers right down now. Although im sure a better smoke system could be implemented.

I like the grass and dirt suggestion and the tyre suggestion is good although i dont think we will get peices of the tyre flying off and you can blow your tyres when drifting although not exactly easy.

The biggest problem with the current smoke system is the smoke particles are not rotated so if you have too many it just looks like a lot of repeating textures.