The inner dual on a trailer’s rearmost axle is out of the driver’s sight and farthest from him. So it tends to be lower on air than all the other tires on a tractor-trailer. Tires on this van are equipped with P.S.I. inflation systems.
 - Photo by Tom Berg

The inner dual on a trailer’s rearmost axle is out of the driver’s sight and farthest from him. So it tends to be lower on air than all the other tires on a tractor-trailer. Tires on this van are equipped with P.S.I. inflation systems.

Photo by Tom Berg

What’s the most neglected tire on a tractor-trailer rig? The one farthest from the driver.  That’s what 40 years in the tire industry tells Al Cohn, formerly with Goodyear and for the last 12 years at Pressure Systems International, maker of the Meritor Tire Inflation System by P.S.I., where he’s director, new market development and engineering support.

Cohn was one of the presenters at P.S.I.’s annual Fleet Technology Seminar Oct. 9-10 in San Antonio, Texas. Tires and tire pressure are like a religion to him, and he shared many insights into what makes them live and die. Attendees at the seminar included truck users, equipment dealers and the trade press.

Most truck owners expect drivers to check and pump up tires, he said, but it’s almost too much to ask.

“It just takes too long to check the tire pressure on 18 tires,” Cohn said. It’s a difficult and dirty job, especially if a guy finds a tire that’s low on air and must find an air hose and drag it out to the truck. So drivers may eyeball and kick or thump one or two, but human nature leads them to give less attention to the ones they don’t see.

Cohn showed a drawing of a rig with typical inflation pressures of the nine tires on the driver’s side. The target pressure is 100 psi, and he noted that the tractor’s steer-axle tire is the one that’s most carefully looked at, because a blowout there can be catastrophic. But check how the pressures vary on the drive and trailer tires.

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Here are Cohn’s conclusions:

  • Air pressures drop the farther you go back on the vehicle. Steers are always best maintained (safety).
  • Trailer tires are always the lowest.
  • Driver side tires are better than the passenger side.
  • Outside duals are better than inside duals.
  • The right-rear inside trailer dual is typically the lowest.

That's why a tire pressure monitoring and inflation device like the one made by Cohn's company is a good idea.

Author

Tom Berg
Tom Berg

Tom Berg

Journalist since 1965, truck writer and editor since 1978. CDL-qualified; conducts road tests on new heavy-, medium- and light-duty tractors and trucks. Specializes in vocational trucks and trailers of all types.

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Journalist since 1965, truck writer and editor since 1978. CDL-qualified; conducts road tests on new heavy-, medium- and light-duty tractors and trucks. Specializes in vocational trucks and trailers of all types.

View Bio
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