I just upgraded my 275/40/19 rear tires to 305/30/19 which are 1.5" smaller in diameter (actually replaced the front 255/40/19 with the 305's as well to make a square setup). A friend suggested going to a shorter tire like this is bad for the differential. He also suggested the car is setup for staggered so I should keep that to decrease front wheel rolling resistance/increase cooling to brakes. This setup is going to be for road course/track use. The PP2 S550 has 305/30/19 square setup, but I don't know if they tune the car differently. I've also read a square setup is better for the track, even though my car came staggered. I feel like gaining front grip at the expense of rolling resistance would be favorable. I guess my main question is will the 305/30/19 setup create issues with the differential? What do others think?