According to TMC,
on-board computer displays of fuel economy can be
off by ±5%.

No fuel-efficient
component is
worth using
unless it saves
more money than
it costs – over
its useful life.

Fuel economy can be 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.

If you can't see it, is it worth doing?

If the fuel economy tactic you're considering is scientifically sound, it's probably worth doing. Just because the effect is buried in noise doesn't mean you aren't saving fuel.

Things change, and what is invisible today could show on your balance sheet tomorrow.

Fuel economy changes constantly

The fuel efficiency of a vehicle changes over time. A new engine may not consume the same amount of fuel as one that's well broken-in, or one that's nearly worn out. Newer-model trucks may have better aerodynamics than older ones. As tires wear, their fuel efficiency usually improves. In fact, the difference between a fuel-efficient tire and a regular tire may almost vanish as they approach 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.

What is your fuel economy now?

One of the most important questions you need to answer is what kind of fuel economy you're getting right now. After all, if you don't know that, how will you know whether anything you try is successful?

As it turns out, the best way to calculate fuel economy is the old-fashioned way: Take a bunch of fuel receipts and the corresponding odometer readings and simply divide the miles by the gallons of fuel.

The word "bunch" is important. The more data you have, the more representative your "average" miles per gallon calculation is going to be.

And, according to TMC, it's probably best not to be tempted by the simplicity of using the computer in the truck, either the dashboard display or the data you download from the computer port.

As TMC says, on-board computer calculations of miles per gallon can easily be in error by as much as five percent in either direction.

On any given truck, the dashboard readout might give you a relative indication of how that truck does from day to day. But it's not likely to give you a true picture. Stick with your fuel receipts, odometer readings and calculator.

Costs & 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, when fuel prices are extremely volatile, the old "rules of thumb" comparing tire costs to fuel costs can be misleading.