Rising fuel prices are taking a toll on Owner-Operators everywhere. Although we cannot control the factors causing this rise, we can control the amount of fuel we use to get each job done. The combination of the laws of physics and how much fuel economy matters to you directly impact fuel consumption.
Many fuel-saving technologies today make it hard to know which are worthwhile. Before spending even more money on a solution, we've got four simple no-cost strategies to help keep money in your pocket when you need it most - pressure up, tighten up, slow down, and back off.
1. Pressure Up
It takes a certain amount of energy to keep a truck running at highway speed. To accomplish that, you must overcome aerodynamic resistance and rolling resistance. The rolling resistance of a tire is defined as the force needed to keep a tire rolling at a constant speed on a level surface.
Pay Attention to Rolling Resistance of Tires
Many factors affect the rolling resistance of a tire and the whole truck by extension. Soft squishy tires are harder to roll than firm tires and they require more energy to keep them rolling. Consider how much harder it is to walk on a beach with soft, deep sand than the firm, tightly packed sand close to the water's edge. It's the same for truck tires, and the more weight you place on the tire, the greater the rolling resistance.
The resistance to movement comes from the tire itself. As it rotates through the contact patch, the inner components of the tire -- the belts, different layers of rubber, etc. – move and deform and create friction between themselves. That flexing and deformation of the sidewall and the tread create rolling resistance.
Think of a single tread block on a drive tire tread; it moves and squirms as the tire rotates. It takes energy to move all those bits of stiff rubber, and all that energy comes straight from your fuel tank. According to Michelin, the tread normally contributes about 40% to a tire's rolling resistance, the sidewalls and belts another 40%, and the bead area about 20.” See the image below. It varies from tire to tire, but you get the idea.
Overall, tires contribute about 30% to a truck's rolling resistance. Again, this varies when accounting for the percentage of aerodynamic drag on an aero truck versus a non-aero design, and the speed and weight of the truck. Most tire manufacturers claim that the lower rolling resistance of their tires will improve fuel economy. The numbers vary, of course, but a rule of thumb suggests that 5% reduction in rolling resistance will yield a 1.5% improvement in fuel economy.
Find the Right Tire Inflation
While investing in low-rolling-resistance tires will lower fuel consumption, simply inflating your tires properly can lead to a reduction in rolling resistance too. Proper tire inflation has a double bonus: it can improve fuel economy and extend tire life by minimizing inflation-related irregular wear. Both will save money.
There are different opinions on how much to inflate your tires. Industry convention says 100 psi for drive and trailer tires is the correct level (steer tires are another story for another day). However, most tire makers' load and inflation tables indicate that 80-85 psi is all you need. Some in the industry maintain that at 80-85 psi, the tire is "soft" and may not be at its lowest possible rolling resistance. That's true to some extent, but you will probably get better life from the tire at the lower pressure.
Like almost everything in trucking, tire inflation pressure is a trade-off. If you want to minimize rolling resistance, 100 psi is probably the way. But don't overdo it. If 100 psi is good, is 120 psi not better? It might be from a rolling resistance perspective, but there are other consequences.
Most aluminum wheel manufacturers rate their wheels for maximum inflation pressure. It's stamped in the wheel for reference and is usually but not always 120 psi. Over-inflating the tire changes the contact patch. Particularly with light loads, it can dramatically reduce traction and cause rapid irregular wear on the center of the tread face and the shoulders.
Check Tire Pressure Weekly
While it's tedious, tractor tire pressure should be checked at least once a week and topped off when necessary. Tire pressure should also be checked on every trailer you pick up. Soft trailer tires will affect your tractor’s fuel consumption.
Remember Fuel Economy When Replacing Tires
And the next time you need to replace your tires, give some thought to more fuel-efficient low-rolling-resistance tires. You have to buy tires no matter what. If your tire choice can help save fuel, it's worth thinking about.
2. Tighten Up
Aerodynamic drag or wind resistance is another fuel economy killer. One of the worst areas on the truck is the gap between the tractor and the trailer. While there are lots of practical reasons for maintaining a certain gap, such as weight distribution, turning radius, tractor wheelbase, or trailer king-pin depth, the gap is often greater than it needs to be. Almost any driver will tell you their truck rides better with the fifth wheel positioned further back and closer to the center of the drive axles. You might get a more comfortable ride, but the increase in the gap costs fuel.
Mind the Tractor-Trailer Gap
Within the constraints of axle weight limits and clearance between the trailer and the back of the cab (including side extenders), keep the trailer as close to the tractor as possible. The actual savings are impossible to quantify because there are so many variables, such as crosswinds, headwinds, the height of the sleeper roof, the length of the side cab extenders, etc., but the savings are there.
Testing performed in the National Research Council of Canada's full-scale wind tunnel about a decade ago showed that closing the gap from 45 inches to 35 inches can save about 150 gallons of fuel per year for zero dollars invested.
Researchers noted that when moving the trailer closer to the tractor, the trim tab on the top of the tractor roof fairing may have to be angled more steeply to direct the airflow over the trailer. They found that air striking the roofline at the front of the trailer significantly impacted the overall savings.
Consider Adding Vortex Generators
If you want to further optimize the savings from reducing the gap, you might consider investing by adding vortex generators to the roof and sides of the sleeper cab or side extenders. These are the small plastic, V-shaped, peel-n-stick tabs you see on many trucks today. They are sold under a variety of brand names at an affordable price (typically just a few hundred dollars), and they have been tested and proven reasonably effective at helping air pass more smoothly over the gap between the tractor and the trailer. You won't see a life-changing difference in fuel economy, but a little bit here and there will certainly add up.
3. Slow Down
Speed has a direct impact on fuel consumption. It takes more energy to move a truck through the air at a higher speed.
Reduce Drag Over 30 MPH
When considering frictional losses from all the moving parts and even tire rolling resistance, that doesn't change much once a vehicle is traveling above 30 mph. Above that speed, it's all about aerodynamic drag and wind resistance. The faster you go, the more drag the truck faces.
That's something to consider when running westbound into a headwind. A 20-mph headwind when traveling at 70 mph is equal to 90 mph worth of wind resistance on a calm day. If you must run fast, save it for trips with the wind at your back.
Factor in Extra Drive Time
Not surprisingly, fuel economy on a non-aero truck will suffer more than an aero truck at higher speeds. If you're piloting a classically styled truck, these higher fuel prices will be even more painful. Can you afford the time to give up even five miles per hour? The better question is, can you afford not? Figures from the U.S. Department of Energy suggest trucks traveling at 75 mph use 27% more fuel than if driving at 65 mph. This is all to say how expensive that extra 10 mph can be with diesel prices - especially as of mid-March, 2022 - they're north of five bucks a gallon and climbing.
Of course, sometimes commercial concerns dictate how fast you drive, but poor planning on someone else's part shouldn't put you in a position to run at a loss just to get their job done.
4. Back Off
No, those aren't fighting words, just a more forceful way of saying try to conserve momentum.
Operate at a Steady Speed
When driving in heavy traffic, it can be tempting to maintain a close following distance to keep all those miscreant lane-changers in their place, but it hurts you more than it does them. You're burning fuel needlessly every time you accelerate to close up a gap in the line of traffic. Your diesel is most efficient when operating at a steady speed, so slow to a bit less than the traffic flow and idle your way along in 4th or 5th gear.
Run Slower than the Traffic Flow
The same thinking applies at highway speeds. Every time you apply the brakes as traffic slows, you're giving up momentum only to give it more fuel to get back up to speed as traffic inevitably picks up again. If you run along a little slower than the traffic flow, you’ll be better able to adjust your speed by coasting a bit by applying just a little brake, thus conserving more of your hard-earned momentum.
Take it Easy on Hills
Backing off also applies to climbing hills, but in reverse. To conserve fuel, climb the hill less aggressively, and when you near the top, back off the throttle pedal and let the truck rollover the crest and down the other side. You'll never notice the few extra moments it takes to go over the top at a slower speed, and you can easily make up the lost time coming down.
Final Thoughts
This type of driving requires patience and discipline. Of course, there are times when you need to run flat out to deliver on time. But it's worth it when you can save a few gallons of fuel along the way. After all, the winner is not the one who gets to the bank first, but with the largest deposit.
Other relevant articles:
Fuel Economy: Part 1 - The Driver Makes All the Difference