I've been thinking a little about getting some bigger tires (285/75/16) Stock is 265/75/16. What do you guys think I will lose if I do this?

 

you can roughly estimate the loss from the percentage increase in rolling diameter.

 

265/75/16 is ~31.65" tall
285/75/16 is ~32.83" tall

The difference is roughly 4% (a little less, actually), so I would expect the difference to be similar to going to a 3.60 gear vs. a 3.73 (not that bad at all).

 

You'll lose the gearing that you've just mentioned, then it will also take more power just to get the additional weight rolling.

When I went from 245.75.16s to 285.75.16s in my Z71, I lost about 8% gas mileage even after I adjusted the odometer for the larger tires.

 

What about in the 1/4, .2 tenths maybe?

 

Depends on how heavy your new tires are compared to the old ones.

My stock 265/75/16s weigh 54lbs. With 285/75/16 Wrangler ATs they weigh 66lbs. Thats 10lbs per rim for 40lbs total. 40lbs of weight on the wheels is "supposed" to be like 8lbs of dead weigh in the truck. Sooo 320lbs? That would kill ya by 2-3 10ths or so. If all the math is correct.

The above doesn't include loss due to diameter/gearing loss.