NEW YORK -- The U.S. aftermarket for medium- and heavy-duty truck parts and components will increase by 3.8 percent annually to $17.1 billion by 2013.

According to a report released by the Dow Jone’s stock market service MarketWatch, the increasing complexity of trucks in addition to rising emission-control and safety-standards will be the catalysts behind the market growth.

The point is, national fleet is aging and fleets are extending trade-in cycles, even as the economy recovers.

However, because OEMs are making trucks better than they used to, most of the aftermarket growth will be spurred by exterior and structural components; mostly, tires, both new and recapped.

According to MarketWatch, “the increased use of new, more durable materials and designs, coupled with the shift toward the use of advanced electronic sensing and control systems, continues to play a major role in reducing medium- and heavy-duty truck maintenance and repair costs.

“Tires,” the report says, “are by far the most important aftermarket product, accounting for more than 40 percent of the total medium- and heavy-duty truck aftermarket in 2008. In fact, tires typically represent the largest maintenance cost for a fleet and often trail only fuel, insurance and driver salaries among all operating costs.

Other products to stock up on: fifth wheels, windows, mirrors, windshield wiper systems and a range of miscellaneous components such as trailer landing gear, bumpers, truck roof and side fairings, trailer body panels and trailer doors.

When it comes to other components such as chassis, drive train, and suspension, growth will be more limited.