Tires and Fuel Efficiency
January 1, 2006
Tires and Fuel Efficiency
High fuel prices not only take their toll at the pump, they affect tire prices as well because oil is a major ingredient in manufacturing tires. One simple and immediate way to make the most of fuel and tire money is to pay greater attention to proper tire maintenance.
Air pressure is at the heart of proper tire maintenance. By maintaining the proper inflation pressure for a given size of tire and load, tires will provide the best fuel mileage and safety, while minimizing wear and maximizing retreadability. Commercial tire manufacturers have tables and charts — available free for the asking — that specify air pressure adjustments for tire size, load and speed.
Inflation pressure is critical because it is the air inside the tire that carries the weight of a vehicle, absorbs shock and keeps the tire in its proper shape so it may perform as designed. In essence, the tire serves as the container for the air. In addition to affecting rolling resistance, and thus fuel economy, inflation pressure also influences handling, traction, braking and load-carrying capability.
Tires are made of layers of fabric and steel cords encased in rubber. These cords provide additional operating characteristics.
Tires flex when they roll, which bends these components, and in turn, generates internal heat — a tire’s worst enemy. Wear is the result of friction created between the road’s surface and the tread as the tire rolls along.
A tire that is improperly inflated doesn’t roll as smoothly or as easily as it was designed to, causing fuel efficiency to fall off since the engine has to work harder to keep the vehicle moving.
Improperly inflated tires have an uneven, irregular tire footprint — that portion that contacts the road surface. This inconsistent shape leads to increased wear, reduced traction and performance, and handling and ride problems.
Underinflation is a major contributor to premature tire problems because underinflated tires cause excessive flexing. There is a direct correlation between how much a tire is underinflated and how much faster it wears. And underinflated tires tend to run hotter, diminishing retreadability.
When a tire is overinflated, excessive wear occurs at the center of the tread because it will bear the majority of the vehicle’s weight. Along with making for a harsher ride, overinflated tires tend to not “absorb” road hazards like debris in the road and potholes as well, increasing the risk of sustaining a puncture or impact damage.
Because improper inflation shortens tread life, tires will have to be changed more often. Along with the expense of purchasing replacement tires, there is the additional cost for tire service and vehicle downtime.
In comparison, air is cheap, and checking inflation pressures doesn’t require a big investment in time.
Tire pressure should always be checked when a tire is “cold,” that is before a vehicle has been driven, or driven less than one mile. Once a vehicle has been driven, tires warm up and experience an increase in air pressure, resulting in an inaccurate reading.
Tire pressure should be checked regularly, at least once a week, and always with a properly calibrated tire gauge. Inflation pressure cannot be accurately estimated by kicking or thumping the tire.
As the Tire Retread Information Bureau’s Harvey Brodsky is fond of stating: “Trying to determine if tires need air by thumping them is as effective as trying to determine if a vehicle’s engine needs oil by thumping on the hood.”
It is good practice to install value caps on all valve stems and to keep them tight. Metal value caps are best, as they contain a rubber gasket to provide an air-tight seal. Most plastic caps do not.
Particular attention needs to be paid to tire pressure in mated dual tire and wheel assemblies. Inflation mismatches on these tires can cause tire diameters to differ enough that the “larger” tire will drag the “smaller” tire. This results in rapid and irregular wear, especially on the “smaller” tire.
What’s more, an underinflated tire on a dual assembly, having a smaller diameter, will shift its share of the load to the other tire. This tire then becomes overloaded, wearing faster and unevenly.
Properly maintaining tires maximizes fuel economy. This saves money at the pump, decreases petroleum fuel demand and reduces emissions and pollution.
Along with lasting longer, tires that are well maintained have improved retreadability. This is significant because retreaded tires provide the same dependable performance and safety as new tires but at a far lower cost — as much as 50 percent less.
Beyond that, retreading actively contributes to helping conserve valuable finite natural resources needed to manufacture tires. For every retread produced, one less new tire needs to be manufactured. Plus, with retreading, tires stay on the road longer so fewer worn tires require disposal instead of many, and this helps reduce scrap tire disposal problems.
Finally, keep in mind that tire selection impacts a vehicle’s overall fuel performance. Because tread depth and design have the biggest effect on rolling resistance, tires should be application-specific. BI
David Kolman is a veteran truck communicator, keynote speaker and long-haul trucker. Commissioned as an Honorary Colonel on the Kentucky governor’s staff for his work promoting traffic safety, he actively participates in trade associations and reports news and information about the trucking industry for broadcasting and print media.
Maintaining tire pressure
Things that can be done to help maintain proper tire inflation:
Fill tires with nitrogen instead of compressed air. Nitrogen allows a tire to retain more of its original properties so there is less inflation pressure loss for a more stable and consistent tire pressure, longer tread life and less oxidation of tire components. This assists in increasing tire life, improving fuel economy and reducing tire aging for a more durable casing for more retreadability.
Use of various air pressure monitoring and control systems. Some warn of low pressure. Others equalize air pressure between tires in a dual assembly. Still others detect when air pressure has dropped and inflate it back to the proper level.