May have been suggested before, but I'd love to see proper wheel-to-wheel impacts. What do I mean, you ask? Well, this for instance:

http://www.youtube.com/watch?v=wvhxlJe_sk4

or...

http://www.youtube.com/watch?v=93G243PZLcA

Basically, any wheel-to-wheel contact would result in someone becoming airborne. It might give open wheel racers a little more incentive to be cautious and defensive.

Anyways, just a passing thought.

yeah, there's already been many discussions on collision detection. Did you search?

They should hire yuji Ide as a consultant for wheel\wheel contact, he's got TONS of experience