Proper inflation is the most important maintenance issue for extending treadlife and protecting casings.

Even if the tire is initially inflated to the optimum pressure, periodic checks and occasional top-offs are needed to maintain pressure.

There are two basic air-loss mechanisms responsible for pressure loss over time. All pneumatic tires lose some of their high-pressure inflation continuously by diffusion through the tire casing. This is, however, a much smaller problem than it was with older tire designs, especially bias ply and early generation radials.

Most quality radial truck tires now employ several layers of diffusion-resistant rubber compounds on the interior surfaces of their casings. Some go so far as to employ multiple components of “barrier” rubber compounds together with traditional tubeless innerliners to further inhibit diffusion through the casing. Two primary advantages are less air loss over time, so less makeup inflation is required, and second, less moisture permeation into the tire casing.

Lower moisture levels retard breakdown of the bonds between adjacent compounds – remember there are as many as 12 different rubber types in some radial truck tires – and between rubber/reinforcement material interfaces. This extends casing life for long-term durability and retreadability. Much progress relating to inflation retention has been made by tire manufacturers.

The second type of inflation loss results from punctures and other mechanical sealing failures. It is imperative that all tire injuries be identified and repaired promptly if tire casing integrity is to be maintained.

Inflation loss and moisture entry into the tire structure are both detrimental to long-term durability. Recommended procedures for tire inspections and repair techniques are well documented and readily available from tire manufacturers, the Technology & Maintenance Council and a variety of retreaders and repair material sources.

Other areas may be overlooked. Dirt, road salt, or other foreign material becoming lodged in the small, annular sealing area of the valve is a consistent problem for some operations. This creates a dilemma, since frequent pressure checks are desirable, but, at the same time, can create leaks that were not present before.

Screw-on, sealing valve caps have been an industry recommendation for years. While they do keep most external debris out of the critical sealing area, removing and replacing the caps can easily double the time required for routine pressure checks. In addition, the small caps are easily lost and difficult to handle in cold weather.

Flow-through caps, featuring a separate sealing area and a protective flange that remains closed to debris entry until depressed by the tire gauge chuck have become popular in recent years. These add a small cost to every tire valve assembly but are generally preferable to traditional screw-on caps, unless a cap replacement program following inflation checks is strictly enforced.

Another concern is debris from inside the tire cavity entering the sealing area. Mounting-lube residue, mold release agents from the tire liner, wheel-well paint particles, dirt from tire interiors not adequately cleaned prior to mounting and other miscellaneous items can lodge in the sealing area during pressure checks. A filtered valve core can eliminate most of these problems. It is a simple device that employs a fine mesh screen on the interior end of a conventional valve core. Some fleets are now considering using the filter cores for all applications, in hopes of reducing valve leaks.

The tire bead/rim seat interface is another area that can be leak prone. Corrosion, buildup from mounting-lube residue, rubber transfer from previous mountings, wheel material erosion, bead seat and flange damage/distortion are common potential troublemakers. Maintenance recommendations available from wheel manufacturers are excellent sources of information to help eliminate inflation loss problems.

Tire pressure monitoring systems may or may not eliminate the valve sealing issues, depending on the system design and location used for sensing pressure. Pressure maintenance systems that provide make-up inflation from on-board air sources may sometimes mask slow pressure losses. These losses, if not detected through periodic tire inspections, can lead to reduced casing longevity.

Remember, the overall goal is to inflate tires properly and keep the inflation contained.