I have a 2013 f-250 xlt 4dr 4x4 6.2L 70,000 miles recently purchased used. When i bought it according to the fuel display i was getting 14.9 mpg then i changed from 275/65r18 tires to 275/70r18 and my display then was reading 10.4 mpg i checked actual mpg myself and i'm getting 8.6 mpg( not towing) i did not have the trucks computer updated for the new tire size, and i'm hearing that the tire size change will effect several things on the truck(fuel mpg, trans shifting ect.) Is this true? And how can i get better mpg? Help please

 

I don't believe the change in tire size is the culprit.

Going from a 275/65r18 Tire to a 275/70r18 is only a 3.4% change in tire diameter. It grows from 32.1 inches, to 33.2 inches.

The 275/65r18 tire spins 629.1 revolutions per mile
While the 275/70R18 spins 608.6 revolutions per mile.
So at 60 mph your speedometer will be off by about 2 mph.

That small a tire change isn't going to mess up your shift points etc. It's not going to cause a 30% difference in fuel economy. I'd start looking for other problems - clogged air filter? Dirty fuel injectors?

 

NutJob has some good advice.

Remember that larger ties are going to take more energy to roll down the road. The speedo being off is going to exacerbate that on your calculations. How does the truck run?

 

the truck runs great, i did have to have a new exhaust manifold put on, but im hearing that seems to be common also

 

Would the the K&N cold air filter help?

 

No. If it can flow enough air to make 385 HP at WOT without undue restriction, it can easily pass enough air on the highway when it's only making 100 HP. Fuel economy claims are a marketing gimmick, you will gain nothing.

 

air filter was changed about 1000 miles ago, it runs great no rough idle or cutting out/missing when driving so i wouldn't think it would be the injectors? any other suggestions ?

 

That is roughly the same results I got when going from a 265/60R17 to a 285/60R17. MPG took a serious nose dive, 1-2 MPG while empty and 1 MPG while towing, even after correcting for the odometer being off.

Despite the small tire in the wheel well look, I went back to the stock size tire. My truck is much happier.

 

Check for a 'sticky' brake caliper.

 

Winter fuel has been notorious for a 2 mpg hit for some. Maybe the fuel change is when the problem started?

 

when you bought it the display said 14.9
Maybe the previous owner reset the average then put a few highway miles on it.
Maybe they had a much different driving style than you.

If you are really getting 8.6 then something is very wrong. I get 8.6 towing an enclosed 9000 pound trailer 75 mph.

 

I'd start checking things. I'm running 33 inch tires that are swamper iroks. I'm averaging 12.5 mpg mixed driving and a lot of slow driving in 4x4

 

at this point i'm not even sure where to begin looking, if it ran bad i would think injectors,everyone is saying the little tire change i made wouldn't effect it that much the only thing i'm leaning toward is someone mentioned caliper sticking, but i've been told if it was i would smell the brake getting hot or wearing it out

 

yes it said 12.0- 14.9 for like 2-3 weeks until i changed tires and rims, and i really don't drive it hard