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Michelin's X-One double-wide tire was designed to replace a traditional set of low-profile duals.

Tires are one of the greatest operating costs of any fleet, right behind personnel and fuel.

And tires have a huge effect on fuel consumption. About one-third of the energy produced by an engine goes to overcoming rolling resistance, most of which comes from tires. To provide traction and comfort, tires must flex or distort their shape. The forces that create this distortion come from burning fuel.

A significant portion of flexing takes place at the sidewalls. Engineers try to reduce this through better designs, more flexible materials, and other improvements. If distortion can be reduced, less power will be needed and fuel economy will improve.

But tires must have some degree of flex. Sidewalls must yield to maintain the tread's contact patch with the ground. Otherwise, the tread will lift, breaking traction. The tread also distorts to roll over uneven surfaces and to transfer cornering, acceleration, and braking forces from the vehicle.

Tires are designed to provide an optimal balance of traction, ride quality, durability, and fuel economy, all at a recommended inflation pressure. If pressure is too high for conditions, fuel economy will improve, but ride, comfort, and longevity decrease. When pressure is below the desired point, excessive flexing wastes fuel and reduces stability.

Too much flexing causes enough internal friction to raise internal temperatures to the point that bonds between components will be lost. If tires are run 20% low for a long enough period, resulting heat will prematurely destroy tire casings. Even if underinflated tires look good, nondestructive testing will show damage that can make them unsuitable for retreading.

Don't test tires by thumping them. Gauge them at least once a week; daily, if you can. Thumping tells you there is air in the tire, but it cannot differentiate between 65 and 105 psi.

Wide range of options

Since flexing consumes energy (fuel) and sidewalls consume the most, it would make sense to cut the number of sidewalls in half. In 2000, Michelin introduced the X-One, a double-wide tire designed to replace a traditional set of low-profile duals. (One 445/50 R 22.5 will replace two 275/80 R 22.5.) Eliminating the second wheel and tire can reduce up to 700 pounds per tandem. The resulting tread contact patch is more square than oval, resulting in better traction but making the tire more susceptible to wear.

Today, a number of tire-makers have wide-base tires. Initially, they were solely for long-haul, over-the-road use, but now there are a number of wide tires suitable for regional and vocational use. These should not be confused with high flotation Super Singles, usually 385/65 R 22.5.

Today's tires are technological marvels that can help or hinder your trucks' performance. They have evolved into highly engineered products, with 25 or more separate component materials and compounds working together in harmony. Tread designs, rubber compounds, adhesives, radial cords, and tread belts are all optimized toward the tire's intended function.

For example, if you opt for wide- base singles, you can get 14-inch wheels with a 2-inch outset. They will improve stability due to the 4-inch wider track, but the offset puts added stress on wheel ends and bearings, accelerating wear. Some axle manufacturers call for reducing axle loadings, or limiting axle loads to 20,000 pounds. That can eliminate any safety margin.

Axle-makers have products made for use with wide single tires. Some are wider so no offset is needed, some have solid instead of hollow spindles, and most have larger bearings. There are weight and cost trade-offs with these axles, partially offsetting the weight and cost advantages gained with wider tires.

A close relationship with the technical people at your tire dealer can be invaluable when making decisions. They can advise about specifying truck components beyond just tires. However, if you ever find a tire dealer pushing product because he needs to make a sale to lower his inventory, meet product quotas, or for some reason other than your best interests, find a new dealer immediately. And consider registering a complaint with the dealer's tire manufacturer.

Tire-makers do their best to support strong dealer-customer relationships based on sound business decisions and, above all, trust. That relationship can do more to keep you on budget with maximum uptime than any low bid price. And, you'll save fuel, too.

Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Association and is on the Board of Truckwriters of North America. E-mailtruckwriter@anet.com.

Read more and share your comments at Paul Abelson's Fleet Factors blog.