New Tires Causing Poor Fuel Mileage

I have a 2011 Tundra 4x4 and when I bought the truck it had factory rims and 285/55/20 BFGoodrich AT's. I bought some Extreme Mudder Rims and capped them with some Toyo's AT 305/55/20's. I also installed a leveling kit. Made the truck look good. The problem is my gas mileage dropped from 16 mpg to 12-13 mpg. A figured the new tires and rims would drop it a little but this seems a little excessive. Is this normal?

 

Leveling kit impacts MPG too; higher up= pushing more air going down the road. Plus the wider/taller/heavier and more aggressive tire impacts the MPG. I dont think what you're getting is out of line. My Tundra stock got about 13 city 18 hwy like it was rated. Lifted 3" and 35x12.50R18's and I'm 10-12 city and 15-16 highway.

 

The Toyo AT 2 in 305/55r20 only comes in their "extreme" tread and is also a 10 ply tire. Long story short, you went to a wider, taller and much heavier tire with a more aggressive tread.
Also lifting the truck and adding wheels with a more positive offset is making you have to push more air going down the road.
I think a 2-3 mpg drop sounds about what I would expect with that combo

 

^^^^These guys above me said it all. Really nothing else to add.

Price we pay to drive a real truck.

It's worth it brother!! Trust me!

 

Yep sounds normal. Mine dropped even more than that with a 3" lift and 35's.
But it looks oh so good

 

Normal and expected

 

To make yourself feel better, you need to account for larger tire size over stock when computing ACTUAL miles travelled. Larger tire size, without a speedo correction, will log less miles in the OD. Ex: 10% larger tire over stock results in a speedometer error of roughly 10%, and associated OD readings of miles travelled by 10%. So if you drive 300 miles on the odometer, in reality you actually travelled 330 miles. Your numbers may vary, as I have no clue what stock tires/speedo fix came with your ride, but you need to refugees those numbers into your mpg calculations