By Paul Abelson
About one-third of the energy an engine produces goes toward overcoming rolling resistance, much 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. If distortion can be reduced, less power will be needed and fuel economy will improve.
But tires must have some degree of flex. A significant portion of flexing takes place at the sidewalls, which must distort to maintain contact with the ground. The tread also distorts to roll over uneven surfaces and to transfer cornering, acceleration, and braking forces from the vehicle to the ground.
Tires are designed to provide an optimal balance of traction, ride quality, durability, and fuel economy, all at a recommended inflation pressure. If pressure's too high, fuel economy improves but ride, comfort, and longevity decreases. If pressure's too low, excessive flexing wastes fuel and reduces stability.
Too much flexing also 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 long enough, resulting heat will destroy tire casings prematurely. Even if underinflated tires look good, nondestructive testing will show any damage that can make them unsuitable for retreading.
Since flexing consumes energy and sidewalls consume the most energy, it makes sense to cut the number of side-walls in half.
In 2000, Michelin acted on this assumption by introducing the X-One, a double-wide tire (445/50 R 223.5) designed to replace a traditional set of low-profile duals (275/80 R 22.5s). They eliminate half the sidewalls and a second wheel and tire, reducing weight up to 700 pounds per tandem. The resulting tread contact patch becomes more square than oval, improving traction but making the tire more susceptible to wear. Also, one wide-base single on a 14-inch aluminum wheel costs less than two dual tires on steel wheels.
Shortly after Michelin's product launch, Bridgestone introduced the Greatec wide-base tire with competitive specifications. Goodyear's subsequent entry for packers (i.e., refuse vehicles) is the G296 in 425/65 R 22.5, and today all three tire-makers offer them for both long-haul, over-the-road and off-road use.
Standard or extra-wide, tires are highly engineered products, with 25 or more separate component materials and compounds working together in harmony. Tread designs, rubber compounds, adhessives, radial cords, and tread belts are all optimized toward the function the tire is designed to perform.
Fortunately, commercial tire dealers have vocational specialists. What they don't know themselves, they can easily get from their suppliers' field service engineers.
If, for example, you opt for wide-base singles, you can get 14-inch wheels with a 2-inch outset. They'll 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 reduced axle loadings or limit axle loads to 20,000 pounds. That can eliminate any safety margin.
What's the best choice for your fleet? You'll have to consider your proportion of on- and off-highway applications, loads, speeds, etc.
Also, axle makers have products made for use with wide single tires. Some are wider, some have solid instead of hollow spindles, and most have larger bearings. Naturally, there are weight and cost trade-offs with these axles, partially offsetting the weight and cost advantages gained with wider tires.
Which trade-offs should you make for your fleet? That depends on your loads, speeds, technicians, drivers, driving surfaces, and if you are retrofitting or have new trucks.
A close relationship with your dealership's technicians is invaluable when making the above decisions. They can advise about specifying components beyond just tires.
One word of caution.
If your dealer pushes product because he needs to make a sale for a contest or to lower his inventory, dump him immediately. You could even register a complaint with the dealer's tire manufacturer. All the high-level tire-maker personnel I know 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 up-time than any low bid.
— Paul Abelson (firstname.lastname@example.org) is a former director of the Technology and Maintenance Council of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.