I have a 2015 mustang GT w/PP. does anyone know if I can fit an 18in wheel on it? Looking for a smaller wheel and more tire.

 

I know that the pp has 19 inch, non pp have 18 inch, you can use 18, if you want to keep the speedometer accurate, you have to use the right size tire with the 18 inch wheels that will have the same height as your 19 inch wheel and tire

 

Just in case you haven’t tried yet, you most likely cannot use 18” wheels with the GT PP due to the brakes. The 15” rotors and Brembos will not have enough clearance with the inner diameter of an 18” wheel.
Fun fact, the ecoboost pp can fit the brembo setup from the GT PP only because it has 19” wheels from the factory. The ecoboosts with <19” wheels cannot.