I'd guess that a 33x12.5" tire will drop your economy by at least 1-3mpg, and maybe more. Especially if you don't regear. A 33x10.5 will be a little better, but it's still a lot heavier and wider than stock tires. Unfortunately building your truck for off-road is kinda the oposite of building it for fuel economy. That doesn't mean you shouldn't try to minimize the mpg loss, but you can't expect to get both.

The wider the tire, the higher the rolling resistance, which hurts economy. The same goes for weight, and tread type. Ever notice the tread on a good highway or Z rated (high speed) tire? All long patterns going the same direction as the rotation. That the oposite of a AT or MT tire. The big lugs cause more resistance. The higher you are lifted, the more air turbulance your truck makes, also causing resistance. The underside of your truck is quite uneven and rough, which causes resistance. Lowering the truck and having a large air-dam directs the air around the truck and reduces friction. Same goes for blocking off as much of the grill as possible with maintaining safe engine air flow. It reduces the high pressure area in front of your vehicle, reducing air resistance.

 

this is what I base my opinion of CAIs on.

 

@ El_Beautor thanks for the advice. You are right about building it for off road is the opposite of a gas saver. i am hoping that i can atleast squeeze some more mpg out of it when i lift it. I want to put 33x10.5x15 on it with a 2.5in suspension lift and prob 3in body lift

 

@ iamchevyman5 i have seen that video before thats why i am so confused about it. Most people say that it helped with their mpg gallon but the video proves different???

 

Use full synthetic oil, K&N Air filter (in stock housing), I use Michelin X Radial tires that get good mileage and long life. Use cruise control as much as possible. Mixed driving I get about 18 MPG and on the Highway I get close to 20 MPG. This is on a 2000 GMC Jimmy 4X4. Avoid quick takeoffs.

 

@ mr.vls
Thanks for the suggestions I will most definitely take that into consideration. What size tires do u have on urs? Any lift also?