It really depends all on stock wheel size vs. aftermarket size you will be going to (8 inch likely) Example, going from a 6-3/8" rear wheel to an 8 inch wheel can gain anywhere from 2-5mph believe it or not (5 mph is a bit of a stretch, but it's possible), but if your wheels are 7" or larger you probably won't gain much. It does help the track roll easier. To show you this, take an old belt and put a tight bend on it and try to roll it across a table, now make the bend larger and roll it across the table... easier with the bigger bend huh?