ok well im thinking about buying a 4inch rcx lift but i want to know some things about 37's, how many mpg am i going to lose?? and i know ill have to re gear it but will i lose allot of power? my truck only has a 4.6.. i have 35's now and its not re geared so id think even with 37's it would be better then 35's if i re gear it right?? just wondering thanks guys

 

Ya if you regear for a little lower than back to stock with 37s your truck should feel way better then it does now with 35s and stock gears. Go for it! But I would upgrade to some heavy duty ball joints.

 

Yes re-gear.

Go with 4.88s or 5.13s

 

O and as for mpgs. With the regear and 37s you should get the same mpgs as you are now. Maybe a little better because your motor wont work as hard as it is now.
The size difference from stock to a 35" tire is way more of a difference then 35 to 37s. The key to making your truck and transmission happy on 37s is the regear.

 

5.13s..? A little overkill imo. The setup in my sig, according to my edge, im averaging 15.1mpg.. thats mixed highway/city/back roads.

To put your truck back to a "stock" ratio..
(New tire diameter/old tire diameter) x old axle ratio = new axle ratio.

Assume your truck has 3.55's stock and had 32" tires stock..
(37/32)x3.55=4.10468 .. 4.10s would be putting youre truck back to "stock"..

 

Well 37s is overkill if you ask me lol, but 4.88 would get you back to about a 4.10 with 38s and sometimes people want to go greater so I suggested the next step up which is 5.13