whats the maxium offset for a 2005 mustang gt. Im looking at some rims that have a +48 offset. their 20x10. gonna go with a 275/40 tire.

 

The higher the offset the more tucked in the wheels are going to be in the well. Stock is 45mm. Some GT500 wheels have a 50mm offset but the rim is only 9.5 in wide. I would stick with 45mm or less. 48mm would probably work in the back if you have an adj to center the axle to maximize clearance.