11mpg difference between city and highway

Normally my truck doesn't leave the city, and my mileage is pretty bad. 13mpg over the winter which by the sounds of it isn't too far off given my climate and city terrain that I drive through.

The weird thing is when I take the truck on the highway I'm getting unreal mileage. Last trip was 24mpg (100% highway).

My question is, how the heck is there such a huge difference? Is my city driving (short trips, steep hills, short distance between lights) a big enough reason? I figure running E load tires might have something to do with it but just wondering if anyone else out there has experienced similar results.

 

What size are your tires?

 

265/75/16E KO2's

 

BFG tires run smaller than advertised. Your true tire diameter is probably 31", if that. Which is a bit undersized for our speedo/odometer gear. Which means the faster you are going the more "over" your speedometer is reading which in turn turns more miles on the odometer.

So if you're calculating your mpg by using the tripometer/gallons consumed, then your calculations are off.

And it's not a linear equation to figure out the difference in actual vs reported mileage. For example, when you're going 30 mph, your speedo/odo is probably pretty close to being spot on, but when you're going 65 or 70 mph, you are probably reading 3 mph faster than actual.

I have 31" tires and have the same issue.

Best way to see if this is your problem is to have a GPS device that measures your speed and compare to your speedometer. I figured out something wasn't right years before I had a GPS device. On a long highway road trip I compared mile markers to my tripometer. It was pretty far off after a full tank of gas.

 

Interesting stuff, thanks for your input. I've been using fuelly which is based on odometer and fuel used. Ill try measuring my actual tire diameter and use a GPS to see if I can get a more accurate picture.