Gears, tire size and mpg - Ford Powerstroke Diesel Forum
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Old 11-04-2011, 12:03 PM
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Gears, tire size and mpg

Just got this truck. It has 37" nittos on it with an 8" ProComp lift. I have a hunch it has the stock 3.73 gears in it.

I am thinking about swapping to 4.30 or 4.56. I'm also wanting better mpg because mine BLOWS (8-9) right now (little womans 06 is getting 14.4 stock with 6" lift, 35" tires and straight 3" pipe). I just ordered an X3 with Innovative tunes. My old thoughts were that if I went with lower gear that my performance would improve, but mpg would get worse, but in the case of these big trucks, lifted, big tires, I think it would actually improve my mpg? Right now at 71mph (assuming my speedo is right and I think it is) I'm turning 1900rpms.

What rpm is considered the sweet spot for highway driving?

I'm going to figure out the current ratio tomorrow. If you have any other ratio suggestions (from your personal experiences) I'd appreciate it. I'm a pretty spirited driver. I want performance and mpg improvements. Thanks for your input.
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Old 11-04-2011, 02:36 PM
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4.30s on the little lower side then stock (lower rpm at speed) and 4.56 just a tad higher then stock, so if you tow heavy often go 4.56, if not 4.30s
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Old 11-04-2011, 08:56 PM
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Agreed with the above! 4:30's best fit unless you tow allot or ar going to do 39 or 40's
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