Ford really appreciates people running smaller diameter tires so they run through their warranty mileage quicker. The speedo is already optimistic by about 3% from the factory in their favor....
Take a look at the wear rating for equivalent tires with just more narrow and wider rubber. You will note that the tire width has almost nothing to do with tire life. Wider tires will float more in winter and in mud, causing loss of control, while narrower tires will tend to cut down to solid surface, but have less rubber on the ground for grip. They both wear about the same in cornering. Wider tires are mostly a lot of hype, and the only things that really matter are compound, tread pattern and siping.
I'm not talking about tire wear or tire warranty, I can assure you that I know all about tires. I'm talking about your vehicle's warranty. It's 3 years 36k miles and 5/60 for powertrain. Since the speedometer is 3% optimistic you are actually putting more miles on your odometer than your vehicle is actually traveling, aka, your warranty will run out faster than it should based on mileage.
