Lift/Tire/Gearing Question

[atvmx21]

Been reading on here for a few years now, learned alot!! Thanks for all the great help everyone.

Anyway, I am planning on getting a lift kit soon, but I have been thinking about gearing and tire sizes. With 37inch tires wouldn't I need to change the gearing in the diff to accommodate the tire size? Wouldn't it make the truck a little worse on gas and slower because of the tires? Is this the same with 35?

Basically, I want a mid size lift kit, but small enough to keep the speed and/or fuel mileage and hopefully not have the change the gearing. Possible?

EDIT: Truck is an 02 f250 crew can 4wd 8ft bed

Thanks in advance!

[Tj Krawler]

Is this going on a F-350 or F-250? As far as gearing goes, with an auto. With 4.10s and 35s, you'll be close to stock tires with 3.73. 37s with 4.30s with be similar. 37s with 4.10s would be close to 35s with 3.73s. Make sense? IIRC stock to 35 loses about 10%, and another 10% going to 37s if you don't regear. With an F-250 (3.73s) I wouldn't want to go to 37s. That would put you around 1450 RPM at 60. Which IMO is way to low. (2000 RPM with OD off) 70 is slightly better at a little under 1700 RPM.

If you want 37s, a 6" lift would be the lowest I would go. 35s can fit stock, better with a leveling kit, or 4" lift.

[Rammstein1224]

you should check this out it seems legit

New Ring and Pinion Gear Calculator (For Larger Tires)