You’ve got to roll with the punches. So do trailer skirts if they are to last a long time, say people who make, test and use them. One such man is Kirk Altrichter, vice president, maintenance, at Crete Carrier Corp. in Lincoln, Neb., who began testing and buying skirts more than a decade ago, when he held a similar job at Gordon Trucking in Washington State. “There are several things” to look for in skirts, he says, not the least of which is ability to save fuel – the main purpose of skirts and other aerodynamic improvers.

Skirts have become common on van and refrigerated trailers, with more than half of all such trailers leaving factories with skirts installed. One estimate says it’s closer to two-thirds. California requires skirts on most semitrailers to reduce fuel use and greenhouse-gas emissions, and current and future federal standards have the same effect. So fleets buy the vehicles with skirts or install them afterwards.

Durability is another thing. “Is it gonna hold up?” Altrichter says. “How robust is it if it comes against docks, curbs, yellow poles” that limit truck movement in yards? “They have to be flexible. I stayed away from metal because they get bent and that’s the end of it. Some have springs in their mountings, but hit one at an angle and they get bent and don’t straighten out. Skirts need flexibility.”

In a test of aluminum skirts 11 years ago, Altrichter found that rivets popped through the skirts’ panels, which rigidly resisted flexing against wind force. In one case, this happened on the first trip.

“Heat expansion” is another potential problem with metal skirts, says Fritz Marinko, vice president, business development, at Stemco, which recently acquired ATDynamics, maker of the TrailerTail and EcoSkirts, which are non-metal. Metal expands with heat and contracts with cold, so mounts need to allow for this, but early models didn’t.

Skirt makers tried other materials and found that thermoplastic and a combination of thermoplastic and fiberglass worked best because they more or less ignore heat and cold, and bend upon impact but spring back into shape afterwards. So they hold up the best, Altrichter has found in his testing and in-service experience with thousands of trailers. Mounting brackets likewise have to flex, so some brands use the same skirt materials for brackets, while others use different but also resilient materials.

Some products have a tall strip of rubber-like material along their bottom edges to absorb most impacts with ground obstructions. Wabash National’s DuraPlate Skirts use a PVC strip that’s very flexible, but the thermoplastic skirt material also flexes inward and outward, then regains its shape. Utility Trailer’s USS, for Utility Side Skirt, uses no lower strip, but its thermoplastic skirting material is highly resilient and its galvanized spring steel brackets bend against inward or outward forces. Videos by Wabash, Utility, ATDynamics, Ridge, Transtex and others show how their skirts bend inward or outward but spring back when the obstacle has passed.

Mounting hardware must resist corrosion from salt spray, too, so nuts and bolts should be stainless steel or hot-dipped galvanized steel, says Marc Bolduc, vice president, business development, at Transtex Composite, maker of Edge products. They should also be SAE-rated, like Grade 5, so they resist shock and wind forces that try to stretch and bend the fasteners. He believes skirts should also look good, so their materials should resist marring by obstacles and waving or rippling in the wind. Thus Transtex’s skirts are stiff yet resilient.

Customers might or might not care much about appearances, and select products accordingly. “It comes down to a personal fleet opinion,” says Marinko. “One fleet buys one brand, another fleet buys a different brand,” based on performance and price. Sometimes a skirt will pick up a long black mark from rubbing against something, but the skirt still works and so does its trailer, hauling freight and making money.”

“Skirts have become a commodity,” Bolduc says, and strong competition among manufacturers has put pressure on pricing. “But the question is, do they hold up? Are parts available, and how good is the warranty – not just the words on paper, but the company behind it?” Prices based on fleet volume have dipped below $1,000 for some products, but better products will cost more. Repairs and associated downtime also cost money, so better products will probably be worth their higher prices.

“Durability far outshadows how we thought they would hold up,” says Marinko. “They’re holding up a lot better than we ever thought they would. Eight years ago, I was one who thought, ‘Oh my God, they’re gonna be nothing but trouble. But they’ve turned out to be very good.”