Tire size
 

I recently bought a 2007 mustang with aftermarket rims. I noticed that the front was 285/30ZR20’s and the back were 255/35ZR20’s. Shouldn’t the wider tires be on the back. Maybe a mistake by whoever installed them last. Or maybe this is ok as is. Just wondering
thanks

You'll definitely want to rotate them front to rear, someone obviously wasn't paying attention when they put them on.

I think they are 20”x10 and 20” x8.5 rims and the wider is on the front. So it should be ok to swap them

Yes, you will be fine to swap them.