Taking care of the Top Two

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As you’ll read in this issue, retreading has become a valuable tool for offsetting most fleets’ number-one maintenance expense (see “Retreads unwrapped,” page 50). But an expense that’s even greater than tires is fuel, and tire maintenance can have a profound effect on fuel economy. The good news is that getting the most mileage out of your tires translates into maximizing mpg.

The importance of proper inflation should be obvious. An underinflated tire flexes more, works harder and robs energy that would otherwise be used for propulsion. Not only can uninflation cost a 3-5 percent fuel economy penalty, it also can lead to a tire’s early demise.

The Tire Retread Information Bureau advises checking all tires as often as possible. Do it when they’re cool, and use a high-quality gauge. It’s hard to go wrong if you maintain inflation pressures based on vehicle manufacturers’ recommendations, which account for weight, speed and ambient temperature.

Another area that can save fuel and prolong tire life is alignment. Misaligned wheels actually fight each other trying to go in different directions. This scrubs away tread and consumes energy. Even slight misalignment, say tire manufacturers, can result in a 1-2 percent fuel economy penalty.

The three major components of alignment are caster, camber and toe. These values can be measured by a variety of means, from string, plum-bobs, protractors and measuring tapes, to sophisticated, computerized, laser-measurement devices offered by a variety of manufacturers.

Caster is the forward or backward tilt of the kingpin or support arm at the top of a wheel-suspension assembly, and camber is the departure, from vertical, of a wheel/tire assembly. While neither has a great impact on fuel economy, incorrect settings can cause handling and tire-wear problems.

Toe, however, can ruin tires quickly and consume excess fuel. Toe is the deviation, from parallel, of the longitudinal planes of the two front tires. If the leading edges of the tires are closer together than the trailing edges, the wheels are toed-in. If the leading edges are farther apart than the trailing edges, the wheels are toed-out. Toe can be measured and expressed in inches, millimeters or degrees of deviation from straight ahead (zero).

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An improper toe setting has a quick and obvious effect on tire wear, so it’s not difficult to detect an out-of-spec condition. If both front tires are evenly worn on their outside shoulders, it’s a good bet that there’s excessive toe-in. If the wear is on the inside shoulders, the wheels are likely toed-out. Toe-related wear, in early, less-severe stages, can show up as feathering, which usually can be felt by hand before it can be seen.

Feathering is a condition where the individual tread ribs wear more on one side than on the other.

If the direction of feathering is on opposite sides on the right and left tires (e.g., left on the left and right on the right), a toe problem is a strong possibility. If it’s on the same side (e.g., on the left side of both tires), you’re probably looking at a camber problem.

Opportunities for misalignment also exist at rear axles. When the thrustline, which runs perpendicular to the center of the rear axle, departs from the geometric centerline of the truck, there is misalignment. And, on a three-axle truck or tractor, each rear axle may produce its own thrust angle, which results in a fuel-robbing and tire-eating condition called tandem scrub.

The upshot is that paying attention to basic maintenance conserves fuel, maximizes tire life and brightens your bottom line. It’s good all around.