Introduction New resources available Theory, controlled testing and the real world

This publication, together with one from TMC, provides comprehensive coverage of the truck fuel economy issue. Bridgestone has been conducting fuel economy tests, under strict scientific conditions, for over 20 years.

As we near the end of the twentieth century, even though the trucking business is experiencing an unprecedented boom, competitive pressures are also at an all-time high.

Your fleet’s survival and profitability depend on your ability to improve productivity and reduce costs. Your customers demand the lowest possible freight rates, just-in-time delivery, and all kinds of other special services, each of which puts pressure on your bottom line.

After driver pay, fuel is probably your number one cost. And anything you can do to save fuel will improve your profitability—
provided it doesn’t cost more than it saves.

Why this Publication?

This is the third Bridgestone publication on fuel economy. The first appeared in 1984, when low profile tires were just beginning to gain significant acceptance. The second, in 1992, coincided with then-new “fuel-efficient tread compound” radials.

Bridgestone has been publishing the results of its tire fuel economy tests since 1984.

Now, low profile radials are commonplace, and most manufacturers offer tires with fuel-efficient tread compounds.

Today, the questions fleets most often ask are:

• How do tires fit into the overall fuel economy picture?
• What effect do new speed limits have on fuel economy?
• How can we select the best tire for our operations?
• Why don’t we get results as large as we see in tests?

We hope to address these questions in this newly revised guide.

New resources available

Recently, The Maintenance Council of the American Trucking Associations published the results of its S.11 Vehicle Energy Conservation Study Group in a report titled The Fleet Manager’s Guide to Fuel Economy. We consider the TMC publication a companion to this one, since it addresses numerous other fuel economy factors not considered here. Copies of the TMC guide are available from:

The Maintenance Council 2200 Mill Road Alexandria, VA 22314 (703) 838-1763 FAX (703) 684-4328 The Fleet Manager’s Guide to Fuel Economy, from TMC, is a comprehensive guide for improving commercial vehicle fleet fuel efficiency, and covers many non-tire-related topics.

To help you find the fuel economy information you need in either book, we have included an index with references to both this guide and the TMC publication. Bridgestone also offers a new video, What Drivers Can Do To Save Fuel, that you can use in your driver education program.

How do we know what we know?

Over the past two decades, Bridgestone has conducted tests at its Texas Proving Grounds in Fort Stockton, Texas, at the Transportation Research Center (TRC) in Marysvillle, Ohio, and at the Tochigi Proving Grounds in Japan.

In addition, we’ve incorporated information from other industry and government sources.

For Bridgestone tests, we have chosen the SAE J1376 procedure. This method produces highly accurate, very repeatable results.

We also include data from “real world” testing conducted by our customers, using their trucks, doing what they do best: hauling freight.

Theory, controlled testing and the real world

In the real world, variables cannot be tightly controlled. As a result, real world fuel economy is substantially less than that measured in tests.

One of the most often asked questions is why the results reported in tests, or in manufacturer’s advertising, are so difficult to duplicate in the real world.

The reason is simply that there are many factors that influence the fuel consumption of a large truck, and most of them interact with each other.
When you run tests, you carefully control as many variables as possible. Speed is rigidly controlled, idle time is fixed. Drivers, loads, trucks, trailers and test courses remain constant throughout a single test. If the wind blows too hard, if it’s too hot or too cold, or if it rains or snows, the test is scrubbed.

In the real world, you don’t have the luxury of controlling everything. One day, you may be hauling a full load of steel castings; the next, a partial load of potato chips. Weather, roads and terrain change constantly.

Care and careful record keeping are critical in accurately measuring real world fuel economy. The worse your fuel economy is now, the more you have to gain by trying to improve it. Both short-term and long-term conditions constantly change—and so does fuel economy.

In addition, as The Maintenance Council points out, when you are calculating miles per gallon or comparing data with someone else, “even the smallest oversight can result in large errors in your calculations.”

“For example,” TMC continues, “a simple oversight resulting in a five-percent initial-fill fueling recording error of a Class 8 truck can invalidate consumption comparisons between units for a year or more.” (Italics ours.)

And, TMC goes on to list a dozen other sources of error that can render fuel economy calculations worthless.*

Because of the way the mathematics works, it’s vitally important that you know whether a given fuel economy measure is expected to DECREASE your fuel consumption or INCREASE your miles per gallon. (The actual math is very similar to the difference between discounts and markups.)

For example, an 18 percent increase in miles per gallon represents only about a 15 percent decrease in fuel use. The bigger the numbers, the bigger the difference.

Who benefits most?

Fleets that have the most to gain from improving their fuel economy are the ones who have the worst fuel economy to begin with.

That’s because mathematically, a given percentage of savings produces a larger dollar amount for heavy fuel users. If you use
$1 million worth of fuel each year and save just one percent, that’s $10,000. If you use $100,000 worth of fuel, that same one percent saves you $1,000.

The good news is, the worse your fuel economy, the more you have to gain by improving it.

All things are NEVER equal

You might think that in the real world, with its constantly changing conditions, variables would cancel each other over time. They
can, but they can also cancel the savings you wanted to get.

It’s a little like trying to follow a conversation in a noisy, crowded restaurant. You can see that the other person is talking to you, but the noise around you may make it impossible to hear.

Fuel economy is often like that. You may be able to find a difference under laboratory conditions, but it may disappear in the real world—and from your bottom line. It gets lost in the “noise” of changing loads, changing routes, changing drivers and changing seasons.

Your investment in fuel-efficient equipment, components and techniques must be evaluated in exactly the same way as any other operational investment. New vehicle designs offer improved aerodynamics and fuel efficiency that can be negated by higher operating speeds.

Even if you could control all the variables, you still might not be able to detect fuel economy differences in the real world.

That’s because the fuel efficiency of a vehicle changes over time. New engines don’t consume the same amount of fuel as old engines. A new truck may have better aerodynamics than one with oxidized paint.

As tires wear out, their fuel efficiency often improves. In fact, the difference between a fuel-efficient tire and a regular tire may completely vanish as they wear out.

And that means, of course, if your tests were done using new tires, the results may be very different as the tires wear, especially with today’s long-lasting truck tires.

Costs and return on investment

No fuel-efficient component is worth using unless it saves more money than it costs—over its useful life (or, over your normal trade-in cycle.) It’s important to weigh the total cost against the total savings. Otherwise, you could lose money trying to save fuel.

And, since tire-related costs are often second only to fuel costs, fuel savings may easily be negated by higher tire prices.

What makes things even more complicated is that some fuel-
efficient components have performance tradeoffs. Making a tire fuel-efficient sometimes compromises wet traction, shortens tread life, increases susceptibility to irregular wear or reduces casing durability. It’s difficult to assign a dollar value to many of these factors, especially the ones that relate to safety.

What’s new in large truck fuel economy?

While certain principles remain the same, advances in technology are radically changing truck fuel economy, as are changes in business conditions. Today’s trucks are much more aerodynamically sleek, have much more fuel-efficient engines, and often are
running at much higher speeds.

All these things affect fuel economy, sometimes in very dramatic ways; which raises new questions that are as much about business as they are about trucks.
For example, is it cost-effective to continue to govern trucks at 57 mph, or should you increase speeds to 70 or 75—if the law allows it? Can you increase productivity by increasing speed, or will the cost exceed the benefit?

In the end, only you can determine what works for you—by running your own tests. We’ll simply give you our perspective—as a tire manufacturer—on these and other issues.