The problem with using dice is the possibility of a really good racer being easily beaten by a really bad one.  In reality, a great racer has much smaller odds of making mistakes than a new driver, but dice give no such advantage to the more experienced.  That would mean that we would all have to have the exact same driving experience (which...we probaby don't).  IE, sharp corners are not difficult, given you know how to drift, slow down in time, etc.  

What I have seen before is this:  A racing RP in which classes separate players based on car class and driver ability (S class, A class, B class, C class, etc).  Both a player's driving knowledge and their selected car factor into what class they are allowed to run.  [i]Then[/i], I feel like it would be fair to assume that all drivers within a certain class have a similar enough skill level and that dice would become a viable determining factor. 

Alternatively, as mentioned, "dirty" drivers, and driving in general, could operate like a T1 arena RP does, where action are posted as attempted actions and reactions are realistic given the circumstances.   

[@Forsythe] I imagine our current car knowledge would have to suffice in placing a modded car relative to its competitors.  If needed I can do that.  Iv'e got 8 years experience as an automotive and small engine mechanic, race motocross professionally, and have been in my fair share of [i]definitely[/i] legal street races.