How much does load affect fuel economy?

It’s the second biggest factor contributing to a tractor-trailer’s fuel economy, following speed.

In the last issue, we learned how aerodynamics and speed affect fuel economy. Imagine an empty conventional long-nosed tractor pulling an empty trailer and how it uses its energy to push through the wind to achieve and then maintain a 70 mph speed.

Now consider that same truck hauling its legal maximum load. It’s not difficult to imagine that same truck consuming more fuel pulling that considerable weight!

But how much more?

If your tractor-trailer ran completely empty, so it weighed around 40,000 lb, you could save 15.5 percent in fuel.

But the point of this business is to haul freight, not empty trailers.

Load 20,000 lb of freight into the empty trailer, so your rig tips the scales at 60,000 lb, total gross weight, and that produces about a 7.7 percent savings in fuel by comparison to the maximum.

Increase the freight to 30,000 lb, so you have a 70,000 lb, total gross weight, and you can expect to save approximately 3.9 percent in fuel. Again that’s in comparison to running at the maximum legal limit.

Using 100 gallons of fuel a day as an example, that saves you almost four gallons.

Nobody can afford to leave 10,000 lb of freight on the dock.

Exactly, but this illustration does prove one thing: maximum payload should always be your primary goal. The trick is to eliminate non-paying load from the truck. In other words, don’t worry about freight that pays. The more weight you reduce that doesn’t pay revenue, the more ways you can increase the amount of freight that does.

Where do I begin?

Take a look at switching to lighter weight accessories. But use a calculator rather than a scale to measure savings. The key is to replace weight saved with revenue-producing freight. If you can’t convert the weight savings into more payload, it probably isn’t worth the time or hassle.

When you spec your next truck, replace heavy steel with lightweight aluminum and composite materials wherever it makes sense, but don’t go so lightweight that vehicle durability is reduced.  These help increase revenue-producing capacity without adding to the gross weight of the truck.  Yes, this can get complicated.

What about tires?

Bridgestone recommends fleets that typically “gross out” before they “cube out.” Consider Greatec wide base radials for the weight-saving benefits.

Again, pull out the calculator rather than the scale to determine if the cost of buying special wheels and possibly retrofitting equipment justifies the expense. Every fleet is different.

If fuel economy is your goal – rather than reducing overall gross weight – you can easily get it back spec’ing fuel-efficient conventional tires, such as those approved for use on SmartWay^SM certified tractors and trailers – Bridgestone M720 drive and R195F trailer radials.

However, if you find you can replace the payload, changing to wide base single tires may be something you need to test.

How can they help?

When you switch from duals to Greatec, you shed the weight of the second wheel and tire on each axle end. Sure, you replace the dual assembly with a bigger Greatec and bigger wheel, but you can still drop a good amount of weight.

Take a look at this chart and see for yourself.

How does this help?

If you haul petroleum, for example, you could add an extra 191 gallons of gasoline or 152 additional gallons of fuel oil.

But we come back to the earlier question – can you make a profit? If your customers are taking all they can and you’re returning to the terminal still loaded, who cares if you can carry extra fuel?

Some fleets have contracts with shippers for specific amounts, and even if you can pull more cargo, the shipper can’t handle the additional inventory.
Yet, maybe you can win an extra contract or two because you can haul 1,964 lb more cargo than the other guy. Or haul 21 more panels of sheetrock. Or 136 gallons of milk.

The bottom line is, reducing weight to save fuel is not a good investment. Spending money that can be replaced by payload is a great one.