Use all lanes?

Yep very much so! That's why you should never have a bye lane unless all cars receive the same lane as a bye. Having a race with random byes will give some a unfair advantage.
 
It does explain things a bit. I always seem to be a bit faster on the outside lanes and sometimes have a case of the wiggles on the inner lanes. I tune on a single lane track or by myself on a multi-lane track. I did add an extra bit of steer to avoid this problem in the upcoming race. Hope it helps...