I was running 275/70 R17 on my 2006 Cummins 4x4 crew cab short box. At this time i got really bad fuel mileage. had injectors replaced and didnt help. Needed new tires so i put on 285/70 R17 because i wanted to fill in some of the gap in the wheel well. But now my mileage dropped almost 4mpg. I cant believe it would be that bad for a 1" taller tire.

Any opinions?

Thanks

 

The new tires are 1" wider and maybe 1" taller. This is only a difference of 3-4% in height, but they weigh more than the old tire. You should not see a 4MPG loss.
Different treads will give you more rolling friction along with the added weight.
Are you going by the onbaord computer?
Do you have a programmer that you can readjust the spedometer to compensate for the larger tire?

I am just about to go with the 285/70/17 on my truck too.
Did it at least fill the gap without rubbing?

 

I did the calculation and it is lower by 3. I also have teh edge programmer and input the new tire size and it had some comment about a change is not required???

as far as the gap i am happy with that. I also installed the leveling spacer on the front springs so the truck sits level.

 

How heavy is the new tire? If it's considerably heavier, if it's a much more aggressive tread, then yes, it could have an impact. I'd be surprised at almost 4mpg though, that's ridiculous. You can tow a 5k pound trailer with less economy drop.

 

Yeah, increasing the size by that little bit won't change mileage a real noticeable amount.

 

Not sure how aggressive the tire is compared to what was on it. It is a Cooper AT3

THe place that replaced my injectors said they want the truck back and they maybe replacing the injectors again to see if that is the issue wih the fuel mileage.