hey i have a question after reading some reviews. some people were saying that if you have a 3.15 ratio truck and you wanted to add bigger tires on it, it will mess up your gas mileage a lot. I have a 2013 xlt ecoboost with 3.15 ratio and was wondering if it was true and if i should change my gears. looking to lift the front by an inch and a half to even out the front and looking to get allied rockcrawler wheels. not really looking to get huge tires just big enough to wehre i do not have to change anything. do you guys think it would effect my truck enough to where i need to change the gears?

 

You will be able to fit 33" tires (depending on wheel offset) but its going to slow you down a noticeable amount with those gears if you go with an aggressive tire. Stock tires are about 31" so if you want bigger 33 would be the way to go. 4 options (in order of my recomendation):
1. Get 33" tires but find light ones (A/T not M/T, like a terra grappler)
2. Get 33" MTs but buy a tune to pep it up and make up for the MPG and power loss
3. Get smaller tires
4. Change the gear ratio (this will require PCM recalibration to adjust the speedometer)