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17.5 hand calced every tank if any town driving is involved, long straight trips 18.5 - 19 mpg at 65-70 mph... Towing 8k+ 11-12. I have a chip but untill I get a few things cleared up I have ran this on the stock tune since I bought the truck and played with the chip mpgs...
The few times I've figured my mileage I've gotten about 16 around town and about 19 on the highway. Driving like a grandma, not too much hot rodding. Towing about 5000-6000 lbs, I think I got about 10mpg. Stock except for 6637. 171k, 4.10's.
I honestly don't know why with 265s you aren't getting more, maybe go 285s lol?
Well, a LT235/85R16E, which is the stock size, is about the same diameter as the LT265/75R16E. The difference between the two is that the LT265/75R16E is a little wider. If anything, I would expect to lose some fuel economy going from a LT235/85R16E to a LT265/75R16E.
Here's a link that will help everybody visualize tire size changes: Tire Size Calculator
I have a 97 f250 4x4, not chipped I usually get about 17 mpg highway. I am running 235/85/R16's. Can't seem to get any better mileage. It has around 57,000 mi. With diesel at $4.33 a gallon I haven't been driving it much.
I run 285's with 4:10's and get 16-17 mpg's empty and about 13 mpg towing 6000lbs. That is with an auto tranny and the common fuel leak. My best mileage either way is with a tune in.
I have a 97 CCLB lifted 35's auto no tune, AFE intake, straight pipe and get 10.5-12 city and 12.5-13 hwy. driving pretty easy - alignment is dead nuts, the truck is just cantankerous.
I do 17 around town.285's 3"and rsk.3"dp4" straight.6637 .no tune or inj.3.55 gears...
But only 17.5 highway .....cant figure why that is not better.with the obligatory fuel leak....argh :-(