Keep ’em pumped!

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It’s almost 2003. Space travel is commonplace. Dispatchers can track trucks to within feet, and satellite radio sounds great. So how come black shards of rubber still disgrace our highways?

Notice I said rubber, not retreads. They usually have nothing to do with the problem. A few years ago, a task force, organized by the Technology & Maintenance Council, collected 1,070 large fragments of truck tires at eight sections of highway, coast to coast. Only 11 fragments indicated that a tire had been victimized by defective retreading.

And other studies have shown that roughly half the rubber fragments found on roadways come from tires that have never been retreaded.

So, what causes tires to disintegrate? Underinflation. Simple, low-tech, not enough air in the ol’ tires.

How? The reinforcing belts in a tire are meant to flex a certain amount while rolling under load. This generates a manageable amount of heat. When a tire is significantly underinflated, however, the belts flex to a much greater degree, and generate enough heat to break down the integrity of the tire. If you’ve ever burned yourself by rapidly bending a coat hanger or paper clip back and forth, you know what I mean.

Often, the casing – belts and all – comes apart. If you see a rubber fragment on the road with wires sticking out of it, that’s not just tread. It’s casing, and it has nothing to do with whether or not the tire has been retreaded.

Also, excessive flexing, induced by underinflation, requires energy, and can reduce fuel economy by a few percentage points.

While the solution would seem simple, the amount of rubber on our highways suggests that vigilant tire-pressure monitoring is not universally embraced. So, if gauging all tires daily poses a time problem, why not let technology work for you? There are affordable, onboard tire monitors and inflation systems on the market, and some can even be spec’ed on new vehicles.

ArvinMeritor/PSI’s external, drive-axle, automatic tire inflation system for retrofit applications (shown), and internal steer and drive-axle systems for OE applications, are scheduled for introduction next spring.

While a few manufacturers offer such systems, I recently enjoyed a visit to Pressure Systems International (PSI), San Antonio. PSI’s trailer-axle inflation system, which is available through a joint marketing and sales venture with ArvinMeritor, Troy, Mich., currently enjoys a 14 percent market penetration at the OE level, and there are over 400,000 units on the road today in some prominent fleets. Moreover, the fleet guys I’ve talked to are very happy with the system, and have reported 30 to 50 percent reductions in total tire costs.

It’s a mechanical system that works like this: Air from the trailer’s supply line is routed to a weatherproof control box, then shunted via flexible air lines to drilled/tapped and pressurized axles. Air then moves to the tires, when needed, through a rotary union in the spindle end of the axles. A dynamic seal, with only one moving part, allows rotation.

In turn, each rotary valve is connected to the tires on a dual assembly via two braided hoses with check valves. For safety, a pressure protection valve between the shut-off valve and reservoir allows air to the system only when the brakes have sufficient pressure (i.e., at least 80 psi) to operate properly.

While on the road, the system automatically keeps all trailer tires inflated to the pressure you’ve dialed into the control box. Inflation triggers a warning light (typically, installed on the trailer’s left front corner). In the event that a leak is simply too big to handle, a check valve will isolate the tire.

While the company constantly uses field experience to improve the trailer system, it is also developing steer and drive-axle systems, which will be introduced soon. These are more good ideas for doing tires, roadways and trucking’s image some good.