I tried used the search but couldn't come up with anything so I am posting this.

My question is what is the widest tire that fits on a stock 2001 dually wheel? I am assuming 10.5" tire will be ok.

Also what is the tallest tire you can run before fuel efficiency starts to degrade horribly?

Thanks for any help.

 

I ran into this on a truck a few years ago, and we found the BFG 315 is narrow enough to clear each other. This customer had custom built wheels on a 6.5 Chevy, but as far as I know the clearances are similar. Any tire shop will get the tires you want and mount them up for you to see if they will clear. If they won't, change shops.
As far as mielage is concerned, I have found a 35" tire with 3:55 gears will be just fine, especially when towing as the longer gears tend to keep the motor in the torque curve longer. I get 12-14 towing 8500LBS at 75-80MPH up at 4-5000 feet in elevation. LE

 

I used to have the 255 85 R16's on my truck which is a 33x10.5. The did not rub or affect the mileage but I felt that there was too much sidewall flex due to the weight of these rigs. I went back to the stock size and all is well.

 

A 255/85? Hmmm. I run a 315/75/16 with 3.54 gears. In the city it absolutely sucks the fuel. On the highway, it just barely sips it. I do have a single wheeled truck though.

 

A wider tire will erase much of the benefit you'll see from going to a taller tire. (more rolling/wind resistance & weight)