Tire Size vs Mileage

[Bolt]

I know this gets covered all the time, but....

I have an 05 6.0 4WD. 265/70/17's in need of replacement.

The best I have ever gotten at 75 cruise is 19.4 MPG. Only once. Usually around 17 if I'm lucky. Farm/town type driving nets me 11-14 all the time. I keep records on every tank.

I want to go with the Michelin LTX A/T2 285/70/17's, but not sure if it will kill my mileage or not. Does the lowered cruising RPM get canceled out by the rolling resistance? Or am I better off going with 265's again? I think they look dinky on the truck, and I could use some more rubber on the farm at times. Thinking about a leveling kit as well.

Also, with the 285 only available in a Load Range D, does it really matter? They have similar load ratings, and the Michelins have 3 steel plys vs. 2 anyways. I do tow farm equipment from time to time, 12,000 lb trailers. Would I still be fine just keeping the 285's properly inflated and rotated?

 

[TampaDieselFX4]

I have an 07 6.0 FX4. with my stock 275's & 20's I got 20-22 hwy at 65-70 cruise. I put on some 35x12.50 Procomp Xtreme AT's (very quiet by the way) and my milage is now 18.5 at 70. So i'm going to conclude my tires killed my MPG's by a SOLID 2mpg. 4" lift & 35's at 70 geting 17.5-18.5mpg. I'm dropping my lift b/c it's overkill for 35's on stock wheels and I'm trying to gain back some MPG's. FYI, 35's weigh 11# more ea than OEM tires.

 

[JRJ04]

i went up to 285/75/R16 (mine came with 16's) and id say i lost about 1 - 1.5 mpg. Now, having the wider tire did help out a LOT in the sand down the beach and off roading in general. Now, is it worth it? If they keep me from getting stuck just one time...its worth it to me. you gotta run the cost/benefit analysis on it i guess...

 

[woofer700]

if you went up in tire size, wouldn't your speedo read a tad slower, that would account for some of the milage, dont know how to figure out the diff, but it would count up less miles

 

[JRJ04]

it would, but even with the approximate recalc that i do, im still averaging about 1 - 1.5 less.

 

[Bolt]

Thanks for the replies. Yes, the speedo would be off a bit, but that can be altered with a little math pretty easily, especially for figuring MPG.

Too bad these are not the answers I was hoping to hear! Haha.