I have never changed the tire sizes on any of my trucks. What would be a good tire size to help my fuel economy. I drive 90% highway miles unloaded. I am getting about 20 mpg at 65 mph. Would like to gain a mile or two more since my job now includes a lot of road miles each week. Thanks for any input.

 

I have 4.10s and I am considering going to 285/75-17 next tire change out.

 

Without a lift the largest you can fit is usually a 315/70 R 17, which is essentially a 35" tire. Changing to the bigger tire saved me 160rpm, which at 65MPH puts me right at 1900RPM. With my truck, I notice a drastic mileage drop when I cross 2000RPM, so this change in itself saved me almost 1mpg. When I added the Smarty JR, I picked up another 1.2mpg.

The 285/75 R 17 is a great alternative. It's a 35" tall tire as well, but 1.5" narrower which reduces road friction and should help mileage slightly. My problem was the only brands I could find (Toyo and Nitto) were almost $1000 more expensive than my set of Firestone A/T, so I ended up with 315's.

I wouldn't recommend removing good tires just to go to a bigger size for mileage gains as the cost takes quite awhile to balance out, but if you're already in need of new tires a larger size will certainly help.

 

Jerry,
Tire pressure and driving speed has the most influence to fuel economy. Due to the aerodynamics, wheel size has limited influence to economy. Good driving habits, highest tire pressure allowed and lower highway speeds make the really big difference. Just bringing speed down to 55 is worth 10%.