Is there an established time or mileage for replacing air bags on air suspensions?” Kevin Tomlinson, maintenance manager at South Shore Transportation in Sandusky, Ohio, posed that question as a panelist during an industry meeting in September. The format of the session, which focused on decision-making, did not allow for an answer — but it’s a good question.

Because trucks, tractors and trailers operate in a wide range of load and operating conditions, there seems to be no predictable life for air springs, shock absorbers, height and pressure valves, bushings, fasteners and the many other parts of an air-ride suspension. Tomlinson, who’s also first vice chairman of the Technology & Maintenance Council of American Trucking Associations, understands that, and also that the session, during TMC’s Fall Meeting, was not designed to get him any answers. One day last month he reported that he had a dry-bulk tanker in the shop to change out its air bags, and discussed the subject.

“We’ve had vehicles that have run a million miles with the original bags, others that went 400,000,” he said. “You never know. This trailer hauls out of a limestone quarry just a few miles down the turnpike and back to a shingle plant right in town. A round trip is maybe 30 miles, and it’ll make five trips a day. It spends more time loading and unloading than running, so doesn’t get many miles. On something like that, miles don’t mean much.”