I have a 99 mustang with stock engine and gearing. I have 225 45r17 tires on the back that measure 24.5 inches. I am confused that on the highway the car does right on 2500 at 70 and is getting around 15 mpg. I did a gearing calculator with the stock gears and I believe the rpm should be a lot lower.
No service codes.
No service codes.