265/70/17 tires with a 4 cyl

So I just ordered up some trd sema rims for my little sr 4 cyl auto. My question is, how bad will the 265/70 tires hurt it fuel mileage wise. I currently have the 245/75/16 hankook ht with steel wheels.
I'm looking at the bfg c rated.

 

Get the Hankook tires that are really super light in that size and you are good to go.

 

Good choice on wheels, those are relatively light at 25lbs. You shed a good amount of weight ditching the steel wheels. Cannot comment on mpg change for that specific setup, but the C-load KO2s are decently light (45lbs IIRC) for an aggressive tire. Of course if not off reading P-load tires like stock will be even lighter.