In regards to the how much? if you want to run a 15 x 10 with a 6.5 back space you need to narrow it 1.50 a side, you can also run 15 x 12 with a 7.5 back space, both require the car to be mini tubed. If you narrow the rear the max 2.5 a side the offset changes by 1 inch less. The only reason 2.5 is max due to not being able to weld the ends on because of the mounts for the lower control arm (you cant get the weld torch in to weld)