When I'm driving alone on the circuit everything is fine, but as soon as there are other cars on the road, the game stutters till the other cars are out of sight.
It doesn't matter if I change the grapic settings, framerate and stuff like that (so I don't think it is coused by the performance of the PC)

Is happens online aswell offline, anyone known with this problem?

Whats the framerate? If it's over 30 all the time i think you might have something running in the background eating the hard disk

Its your frame rate. Its probably too low. Best thing to do is update your vid card. However, if the sound is stuttering, and the gfx freezing, thats different issue... for me it was hdd was too slow (but it also occurs in windows).

Ven