ACC is based on a real racing series, thus they are using data coming from real manufacturers such as Pirelli and the car manufacturers themselves.Lol, they have essentially shot themselves in the foot by outlawing mods. I do not have the game but this certainly does not foment interest.
I think ACC is doing just fine as a racing simulator based on the racing series from SRO.
What we can assume is that Assetto Corsa 2 (or 3 depending if you count ACC as AC2), will have support for modding just like Asetto Corsa.