When it comes to tires, the primary consideration for most operators is resistance to irregular wear, while obtaining the highest overall tread life. So when we're talking about spec'ing trailer tires, we need to focus on service condition, especially the frequency and severity of trailer-axle side scrub.

Long-distance, high-speed rigs with minimum local delivery work will benefit from the current generation of trailer-axle-specific tires with premium casings and shallow treads. Since rolling resistance improves with reduced tread depth, and the tire contribution to total fuel economy increases for free-rolling tires at steady speeds, these tires offer improved fuel economy compared to deeper tread options.

Shallow tread tires also tend to reduce irregular wear in the absence of high lateral forces in the tread footprint area. In addition, many operators report lower operating costs when trailers equipped with air-ride suspensions are spec'd with shallow tread tires.

Deeper tread tires, such as those used on steer positions of linehaul or metro service power units, are good choices for vehicles used in local delivery applications, where there's lots of tight maneuvering in congested areas. These high-scrub conditions can create fast wear rates and unacceptably low removal mileages when shallow tread tires are used.

However, avoid deeper tread tires with de-coupled or undercut shoulder ribs. While these units are designed to reduce irregular wear on linehaul steer axles, they may be susceptible to shoulder rib tear in high-scrub trailer service, especially on tandem axle units and trailers subjected to frequent curbing.

Special consideration must also be given to tire selection for spread axle trailers. These configurations can create very high degrees of tire side-scuff when turning, and generally require deeper treads with solid shoulder ribs to achieve satisfactory tread life. Some tire manufacturers even produce specialized low-tread radius tires (more rounded shoulders) for these applications.

Another factor relevant to tire selection is trailer loading, since tires deliver optimum tread life when operated under consistent load conditions. When runs are light or empty, irregular wear can occur. The above guidelines should be used for operations in which the trailers are usually loaded, including most diminishing load delivery uses. But if empty returns make up a high percentage of trailer mileage, irregular wear should be monitored closely.

Maintenance of trailer tires should also be reviewed periodically. Many cost-conscious operators have recognized that the investment in premium radial trailer tires often justifies additional maintenance. The trend to OTR diesels that favor higher torque ratings also affects maintenance, since the transfer of driving torque tends to "age" tire casings over time. Therefore, it makes sense for many operators to retread used drive tires for free-rolling trailer positions, and retread high-quality trailer tire casings for drive tire service.

With the development of axle-specific tread designs for both new and retread tires, and the use of premium casing types on all positions, it's more important than ever to consider a comprehensive tire program for all wheel positions. Spec'ing tires for power units and trailers separately is not good for your bottom line.