Originally Posted by dutd33
Just out of curiosity, a friend told me that bigger tires will actually give you better mileage, is that true?
A larger outer diameter on the tire? Highway gas mileage, yes. But you need to watch out for tire rub and bottoming out on bumps, etc. It also causes higher stresses on the engine/clutch/drivetrain as the car will be receiving higher loads than expected at the theoretical speed. So your odometer will be off and if something breaks, Ford could deny warranty claims.
That said, it lowers your city has mileage because the car requires more work to stop and go. Look at the tires on cars like the Tata Nano, Yaris, etc. They’re relatively small for a reason. The only times bigger tires help gas mileage in city driving are when you have a hybrid with regenerative braking. Then, the car can regain this otherwise lost energy. But, generators are not 100% efficient, so you will never gain as much energy as you spend if you just had smaller tires from the beginning. Did that make sense?
EDIT: Otherwise, keeping the same OD and getting bigger rims will lower gas mileage as will a wider tire.