:hail::hail::hail:
The effect of gearing on gas mileage is a little more complicated than that. In this case, given a six speed transmission (and the auto will do better because it will aggressively upshift in light driving), the effect on mileage will depend on the type of driving. Highway mileage will certainly drop, especially over 65 mpg) but city mileage will improve because the higher gearset will improve mechanical advantage and require less gas to move from a stop; the transmission will move through the gears more quickly, but there are more than enough in a 6 speed. Suburban mileage (~40 mph) should also improve because the car can simply move into 6th gear where it would normally travel in 5th with the 3.15's, and again will benefit from proceeding from a stop.
I asked the Ford rep this question when seeing the 2015. He agreed. If the 18s fit on the base GT they will fit on the PP.
It's much cheaper to buy a second set of 17" or 18" wheels for snow tires. Take-off GT wheels are good, as are V6 wheels that show up on Craigslist regularly. Not only will the snow tires be cheaper, but saving the cost and hassle of swapping four tires on and off the wheels twice a year really adds up.
I asked the Ford rep this question when seeing the 2015. He agreed. If the 18s fit on the base GT they will fit on the PP.
I was really not wanting to buy 19" snow tires
Well my brother works at Big O so I get rotations and mounts for basically free. Plus big discounts on tires (:
I'd use those. The rules for snows are different. A high performance snow tire around 225-65-17 or so would be ideal. Thinner is better for snow traction, though obviously too thin would be a problem on dry roads. 225-65 would be a good compromise.
The Ecoboost comes standard with 3.31 (not 3.15), so from that to the 3.55 is negligble for Mileage. 5th and 6th gear on the MT82 are both very tall, and this is even more so for the EB. I drove a '13 V6 and 6th at 70mph was too much lugging for me. Also, others on this site have reported that the MPG's are determined using the highest gearing, so if that holds true you dont even need to worry about the fraction of an MPG youll be losing.
As for the wheels, I would add that 19" rims are heavier and tax mileage, although this will also be negligible given factory 18's are not a good deal lighter. If you want a noticable difference in mileage from the wheels, you can find 18" wheels as light as 21 or 22lbs each on tirerack, where the factory 18/19's come in between 28-32lbs each. The car would feel lighter on its feet and accelerate a hair better. Squeeze out maybe an MPG, save the 19's for special occasions?
