One Thousand Miles in a Gas Truck

Coast to coast, if you count Lake Michigan. Fun fact: Lake Michigan is the only one of the Great Lakes that is not part Canadian.

We spent much of the winter traveling across the Gulf states: Texas, Louisiana, Mississippi, and Alabama. We needed to head home to Indiana to take care of some things and get ready for spring.

Our last thousand miles was a pretty straight northern trek from the gulf near Mobile Alabama up to Lake Michigan, taking I-65 almost the whole way. We started at sea level, climbed up to the outer edge of the Appalachian mountains in Northern Alabama and Tennessee, and through the windy flatlands of Indiana.

Obviously we got much worse mileage in the Appalachian foothills, right?

Results

Total miles: 1,024

Fuel Cost: $507.82

Total fuel economy: 6.8 mpg

Route: Starting near Mobile AL on the gulf coast and ending in Northern Indiana near the shores of Lake Michigan

Day 1: Mobile to Northern Alabama

Terrain: Good roads, some up and down, gradual climb to 500+ ft

Weather: high 50°s and sunny, low wind

Fuel economy: 7.1 mpg

Day 2: Northern Alabama thru Tennessee to Louisville in Northern Kentucky

Terrain: Ok roads, foothills of Appalachian mountains, plenty of medium climbs

Weather: Mid 40°s and sunny, low wind, some rain in parts

Fuel economy: 6.8 mpg

Why did fuel economy get worse the second day?

Rain + cooler temps increases rolling resistance on tires
Rain + cooler temps keep drivetrain from optimal temps
Climbing grades

Day 3: Indiana

Terrain: Bad roads and angry drivers

Weather: Around 30°, windy in parts

Fuel economy: 6.4 mpg

Why was flat Indiana the worst day for fuel economy?

Cold temps increases rolling resistance on tires
Cold airs keeps drivetrain from optimal operating temps
Potholes and rough road slow momentum
Bad drivers and construction make it hard to maintain consistent speeds
Windy enough for turbines

Let’s dig a little deeper into the factors affecting fuel consumption.

Road Quality. Rougher roads mean more rolling resistance. And then the potholes take away your forward inertia. With rough winters and a small road budget, Indiana roads are frustrating.

Bad Drivers & Traffic. Consistent speeds are good for fuel economy. Slowing down and speeding up because of other vehicles will bring down your numbers.

Inclines. Your engine has to work hard to overcome gravity to make it up a hit or overpass.

Wind. I-65 goes through a wind farm in the north part of the state. There are not many trees to deflect the wind from the road. Even though the terrain was fairly flat, during this stretch the truck rarely got past 8th gear. Whether gravity or wind, any time you have a force pushing on your rig in a direction other than the way you are headed, you are going to spend fuel to overcome it.

Temperature. Heading north in the winter means cold temperatures. Tires, differentials, and all the other spinning parts of the truck have a not-too-hot not-too-cold Goldilocks zone. Imagine the oils in your truck being like butter for your toast. Too cold and its hard to spread. Too warm and it won’t stick where you want it.

Rain. While we only had a bit of rain on day 2, and I don’t think it had a major affect, but it can also have a major impact on fuel economy. Wet roads both increase rolling resistance and cool down your axles & differentials under the vehicle resulting in the Cold Butter Effect™.

Conclusion

By spending a little time to track fuel economy on a long trip, I was able to gain a much improved understanding of the factors that affect my vehicle's range and operating cost.

I love this truck. It’s a lot of fun to drive with or without a trailer. I know I’m giving up a bit of towing comfort by not having a diesel, but I don’t tow every day. Around half our miles are without the trailer. This is the right ride for us.

Links:

Freightliner article on fuel economy in semi trucks

Highway fuel prices nationwide at Pilot/Flying J