Help with milage

I just put 285/75/17 nitto trail grapplers on my 01 tacoma. Speeds over by about 3-5 mph. When im checking my gas mileage what should i be miles times # to get my true miles. they measure 34.1X11.59 i think according to nittos web site. Thanks

 

If you have an ultra guage or scan guage it will help you out. I'm not sure on the equation needed to figure that out

Also, I would think that a UG or scan guage would be more accurate because the size of the tire differs due to weight/ rim width/ air pressure. Tire companies usually run their sizes a little bigger than they really are.

 

I know before with 33 claws someone said 1.08 but not sure if this is more. my claws never effected my spedo but by a mph or 2 max

 

My truck is on 33/10.5/15 km2's and according to my ultra guage I'm off by 1.122. So when I get 220 miles per tank (according to my dash) I'm really getting 247 miles for that tank. Again this is all through my ultra guage which I hope is accurate.

 

I installed my lift and 33"s back in 2008 and I have no idea how many miles I have on now haha.

 

Yea I know my speed im just tryin to see how many miles im really going so I know my true mpg. I did it time 1.08 yesterday and was gettin 16.85 on the first tank with the new tires. I just feel im probably going further then the .08 with these new tires.
Is there a chart or something that will tell me?