Why do my LT235/85R16 get GREAT mpg & 31x10.5s suck mpg

[meyek91974]

I had a 97 4door 4wd that I put 31x10.5s and I got around 12mpg and now on my 99 EB I put LT235/85R16s to have a bigger/taller tire and my center console tells me Im getting 28-31mpg when Im on the highway.

Is it because they air up to 85psi (I usu go about 75psi)? because they're about 3/4 inch narrower? cause the tread is linear? They're tires from an electrician's box work truck Or ???? combination of all

I know when I have them aired up & I put it in N I can push it with my thumb once I give it the initial push.... but rpms & gear ratios would still make the engine run the same RIGHT???

 

[my98nnj]

Tire pressure is vehicle specific, which means what's on the sidewall is the tires max load rating. You're way over inflating them to the point your traction is being compromised. (Less foot print) Thats why your MPG is different.

You should be running around 35psi max for daily use.