Originally Posted by TopGun

what hes saying is....lets say you went from a stock 31 inch diameter tire and you were getting 18 mpg on the computer, using the formula for circumference "C=(pie)x(diameter)" then the circumfernce of a stock wheel is C=3.14x31 which equals 97.34 inches which translates to 8.11 feet. so in the trucks mind for every rotation of the axel it has traveled 8.11 feet. in actual reality you traveled 3.14x35= 9.16 feet with that one rotation. There are 5,280 feet in a mile. So in your trucks computer stock its saying with 5,280/8.11 feet=651 rotations of the axel per mile, and you can go 18x651=11,718 rotations per gallon. now lets say you lifted it and put 35's, earlier we figured out that your going 9.16 feet per rotation. the computer is reading 16 mpg now since you changed tires...so that comes out to 16x651= 10,416 rotations per gallon. sucks we have less axel rotations per gallon now! but wait, we are traveling farther per rotation, so lets figure out what 10,416 rotations x9.16 feet = 95,410 feet traveled which comes out to be in all actuality 18.07 mpg! (95,410/5,280)=18.07. Now if you think well I dont use the computer I calculate manually, then just remember your odometer is still gonna show how far you traveled by counting one rotation as 8.11 feet and not 9.16. so thats off too. good news is...when your truck hits 100,000 miles....its actually got 113,000 miles on it! talk about extended warranty! sorry if this post is boring and or hard to read.

Originally Posted by shortride

For those that haven't bought your new truck yet or thinking about trading for a newer model and you are going to mount the larger out of factory specified tires you would be a lot better off if you opted for a 3.73:1 or may even a 4.10:1 rear-end ratio.

Originally Posted by twowinns

I ordered the 3.73 and am thinking of switching from 275/55/20 to 285/60/20. Ford didn't offer a 4.10 for a F-150, so I'd need to upgrade with an after-market set-up? How much is that likely to cost me?

Originally Posted by Skandocious

You can get 4.10s on an FX4 with EcoBoost (or a Raptor) but I don't recommend it on the EcoBoost unless you're going with much larger tires. I think the EB is much better matched with numerically-lower gearing.

Originally Posted by TopGun

what hes saying is....lets say you went from a stock 31 inch diameter tire and you were getting 18 mpg on the computer, using the formula for circumference "C=(pie)x(diameter)" then the circumfernce of a stock wheel is C=3.14x31 which equals 97.34 inches which translates to 8.11 feet. so in the trucks mind for every rotation of the axel it has traveled 8.11 feet. in actual reality you traveled 3.14x35= 9.16 feet with that one rotation. There are 5,280 feet in a mile. So in your trucks computer stock its saying with 5,280/8.11 feet=651 rotations of the axel per mile, and you can go 18x651=11,718 rotations per gallon. now lets say you lifted it and put 35's, earlier we figured out that your going 9.16 feet per rotation. the computer is reading 16 mpg now since you changed tires...so that comes out to 16x651= 10,416 rotations per gallon. sucks we have less axel rotations per gallon now! but wait, we are traveling farther per rotation, so lets figure out what 10,416 rotations x9.16 feet = 95,410 feet traveled which comes out to be in all actuality 18.07 mpg! (95,410/5,280)=18.07. Now if you think well I dont use the computer I calculate manually, then just remember your odometer is still gonna show how far you traveled by counting one rotation as 8.11 feet and not 9.16. so thats off too. good news is...when your truck hits 100,000 miles....its actually got 113,000 miles on it! talk about extended warranty! sorry if this post is boring and or hard to read.