Check your alignment...
 

I had been noticing a slight decrease in my FE as compared to last year. I recently took a long highway trip in my MMH and noticed that I was also seeing a significant reduction in my fuel economy there as well. I was unsure what the cause might be, and aside from my tire pressure being a couple psi below normal, I was stumped.

I just had my MMH in this week for a service visit and to have the recall for the HV battery harness done. While there the service manager recommended I have the alignment done. I agreed and the tech came back to say that the alignment in front was WAY out of spec. I certainly hit my share of potholes and uneven road surfaces here in Philly so that wasn't a huge surprise.

That led me to wonder if a poorly aligned vehicle could have a 1-2mpg impact on fuel economy. If tire pressure can, and roof rack cross rails can, why not misaligned wheels?

Thoughts?

Re: Check your alignment...
 

Huh, never thought of that, but now that you mention it I don't see how a misalignment wouldn't affect your FE.

If the camber were in or out (the vertical tilt of the tire), the pressure on the tread wouldn't be directed squarely down on the road - it'd be on the inside or outside of the tire which is not where the tire is designed to be loaded. The steel belts in the tire would be trying to push/pull the tire back to the center of it's "comfort zone".

I'd also be similar if it were toe in/toe out (think of your feet - with your toes either in {pigeon toed} or out {duck-footed}). The front tires would not be both pointing in same direct line of travel, so one or the other would be causing friction by trying to "pull" the car in the direction it's aligned and trying to make it go it's way - so the car would actually be working against itself a little bit.