So one thing I have noticed with my 3.5EB Crew w/6.5 bed and 3.55 gears, is that when I had Michelin LTX M/S2's on my average MPG was 17.8 to 18.1 60/40 city/hwy respectively. On a pure hiway trip I would get 20-21 all the time. At 54,000 miles I put a more aggressive tire on, the Cooper A/T 3's and since then I have seen my mileage decrease to 15.5-16.7 and hiway down to 18.9-19.5. The more aggressive tread seems to create more rolling resistance thus a 10% decrease in fuel economy. Tires do make a difference.

Mark

 

Good post Mark, tires make a difference!

 

Check your odometer. I put "low rolling resistance" tires on a Subie recently and got about a 10% increase in MPG. Then I found out they are at least 5% smaller in rolling diameter than the same sized tire that was on the vehicle. So, my increase in MPG was partly due to not going as far on each tank as I thought. Perhaps your tires are bigger in diameter and you are going further than you think?