Mpg loss with small tire upsize
 

Is this right, immediatly after the switch from stock GY 18"s I went to 285 65 18"s BFG A/t ko ( love them BTW) what I don't like is a 2 mpg loss consistency with no change in driving habits or conditions. Is this possible from such a small size change( I think a half inch wider and taller).

Two things to consider. Number one, did you adjust your speedometer/odometer? Some of your "loss" may not be accurate as you may have traveled further than what you are registering. Second, not only do those tires slightly change your drive trane ratios, but they probably weigh more than your other tires so a slight loss is probably to be expected. Chances are if your gauges have not been adjusted yet you will get some of your calculated loss back. Enjoy your new shoes.

You can't expect bigger tires to increase mpg or even keep it the same.

yes just be glad you only lost 2mpg

The biggest factor may be that the BFGs are a much more aggressive tire. Combined with the speedometer being off and the increased width and height, that isn't surprising.

What tire pressure are you running those tires at? If 35 or even 40, that is too low for them. They should be run at about 50, and no lower than 45. If your old tires were P series, then you can expect a slight drop going to LT tires, no matter what pressure you run. Those are a LR E with a max of 80 and need to be run at the proper pressure for them. Also they will have a bit more rolling resistance.

more weight per tire ...2mpg......what is that 50 miles a tank?

LT E rated tire , at 60psi all round, no changes to speedo (don't know how) and a loss from 434 miles/tank to 372 a tank. from what i read so far could be normal due to the new weight of the Erated tire and tread pattern.

Actually 60 may be a little high. You will probably get excessive wear in the center of the tread with that, unless carrying a load. I would lower that to 50.
Tire size can only be reprogrammed by either the dealer (who would not have that tire size available) or an after market programmer. However the difference between the 275 and 285 are negligible. Not that big a difference to make programming worthwhile. Use one of the programmers on the sticky at the top of the page to get the real difference. I think you will find the difference is about 1/4 of an inch, which would be less than 1%. At 65 on your speedo, you are actually going 66.

60 psi and it will beat your brains out driving it

i ran my Erated tires at around 45 and it was good for me