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Measuring the Benefits of Proper Spec’ing.


Heavy-duty truck tires generally fall into three categories: steer tires, drive tires and trailer tires. Proper maintenance of steer and drive tires is relatively simple, but trailer tire maintenance tends to be more of a challenge; primarily due to the fact that trailers are usually rotated or released frequently throughout a typical delivery route.

Effective tire management is a key factor as it relates to efficiently operating a fleet of heavy-duty trucks. Air pressure, rotation, vehicle alignment and speed are the four key elements that contribute to the extended life of a tire.

Air pressure in a tire impacts the fuel economy of a vehicle and tread life of the tires. Studies show that vehicles typically experience a 1% reduction in fuel economy for every 10% of under-inflation in the tires. Such a small percentage may seem trivial until you factor in the number of tire positions, the number of trucks in a fleet and amount of miles run each year. Severely under-inflated tires can also lead to as much as a 50% reduction in the life of a tire.

Periodic rotation of the tire and proper vehicle alignment extend the life of a tire by reducing irregular wear; which also contributes to smoother performance and increased fuel efficiency. Rolling resistance is directly related to the speed that a vehicle is traveling. Every mile per hour (mph) increase in speed above 55mph results in a 2% reduction in miles per gallon (mpg). Increasing the average speed of a vehicle from 55mph to 65mph will result in a 22% increase in fuel consumption, while only reducing travel time by 18%.

Ultimately, improper tire maintenance will lead to irregular wear, higher thermal and mechanical fatigue of the casing, lower re-treadability and even premature failure. Understanding how to properly spec the different types of tires on a tractor-trailer combination is essential.

On a typical heavy duty rig, trailer tires contribute as much as 50% to the vehicle’s overall fuel economy; with steer and drive tires accounting for up to 20% and 40%, respectively. Trailer tires have the most significant impact on a vehicle’s fuel economy and there are more of them in the average fleet in America; so, properly selecting the appropriate trailer tire for a particular operation is paramount.

It is also wise to take into consideration the primary operation of a given fleet or vehicle. Long haul, medium haul, regional, on-off, off road and winter operations each have a unique set of parameters to be considered as it relates to the design and construction of tires (and trucks, for that matter). For instance, the cut and chip resistant compound found in an on-off mixed type tire would wear out rapidly during a long haul operation, where high speed and elevated temperature are the standard.

There are versatile tires that offer a fair balance between two operating conditions that are fairly close in the spectrum – like medium haul and regional, for example; but a fleet must make several careful considerations when selecting tire patterns and compounds. The tire industry has moved in the direction of developing ultra-specialized products that meet precisely meet the needs of specific service options; therefore, accurately defining the fleet’s operational range is of utmost importance.

Wheel position also adds a number of variables to the tire selection equation; steer, drive and trailer tires usually require a variety of different tread and compound combinations.

For example: steer tires typically experience high levels of mass transfer while breaking and cornering. As a result, it is wise to select tread pattern that will support elevated lateral forces during normal handling, cornering and by wind drag; drive tires experience high levels of torque because they are attached to the axle, so deep treads and blocks in the central tread are common features; trailer tires do not steer the vehicle and are not driven by the engine, so torque is not a factor. Shallow tread, strong solid shoulders and special compounding in trailer tires result in longer life, low irregular wear and low rolling resistance.

With the implementation of an effective tire maintenance system fleets can track the results of any changes they make in tire selection. Over time, measured improvements will illustrate the benefits to good tire management.

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