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Commercial Tires

The Air In There

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The Air In There

We’ve discussed a number of tire selection, maintenance and technology issues
in this column over the last 18 months. Over this period, roadside tire pieces have continued to figure prominently in news reports and studies conducted by parties inside and outside of our industry.
Some reflection and updating on the basics of pneumatic tire inflation clearly is in order. Plain and simple: tires don’t function without inflation pressure. Equally as simple: inflation pressure management remains the single most important maintenance-related element for any trucking operation.
While so-called run-flat tires have been developed for automotive applications, using highly reinforced sidewall and bead areas and specialized fatigue-resistant materials, such tires operate under much lighter loads and lower inflation pressures.
It’s generally accepted that current run-flat designs are not compatible with the requirements for high speed over-the-road truck tires, which operate at three times the inflation pressure and carry much greater loads than the smaller tires. There are some heavy duty run-flat systems, developed primarily for military use, but they tend to be expensive, add considerable weight and rolling resistance, and are difficult to service.

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Getting to Right

Regardless of run-flat technology, maintaining proper inflation consists of five separate considerations:
®′ Using the proper inflation medium
®′ Getting it into the tire
®′ Setting the correct pressure
®′ Keeping it in the tire
®′ Monitoring any pressure loss
Funk and Wagnalls define pneumatic as “pertaining to or containing air or gas, especially compressed air.” Alternative gasses, most notably nitrogen, are occasionally used to inflate commercial tires, usually to reduce the possibly of fire or explosion in the event of overheating caused by excessive loading, high speeds, or aggressive brake use. OTR equipment and heavy off-road hauling account for the majority of these applications, though some smaller fleets are experimenting with nitrogen for on-highway applications.
The performance and safety benefits of nitrogen vs. air have been argued for decades. And there have been few real-world studies done on the possible benefits of nitrogen. Nitrogen is still touted in many corners, but most tiremakers and fleet managers question the benefit and convenience. One major logistics issue is that even a small percentage of non-nitrogen make-up inflation (e.g. truckstop service) negates any claimed benefits. For now, let’s concentrate on compressed air in non-runflat tires.
Dry air is very important to tire casing longevity. Have you ever noticed that mounted snow tires usually need to be topped off after storing them?
Some high-pressure inflation is diffused through all tires over time, carrying available moisture with it. Moisture contained in inflation air is detrimental to the bonds between internal tire components, and can also cause corrosion in areas around punctures and repairs where reinforcing materials have been exposed. Not to mention corrosion around the interior of a steel wheel. Higher amounts of moisture/water can actually cause an out-of-balance condition and resulting vibration.

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Dry Out Your Air

Correct plumbing of air lines should include drop legs below the level of air takeoff. Primary water traps or collectors at compressor outlets are essential to collect much of the moisture produced in the compression process. However, smaller filters at the end of the air line, just ahead of the inflation chuck, are highly recommended and sometimes overlooked. An extra bit of insurance is available from filters specially designed to cut off airflow if excessive moisture is present.
A high flow rate of air into the tire, coupled with proper use of lubricant, is helpful in obtaining the most concentric bead seating and, therefore, the most uniform tire/wheel assembly. Some new truck manufacturers don’t actually use the valve for first inflation, but rely on computer calibrated high-pressure air blasts directed into the tire between the lower sidewall and rim flange for rapid bead seating.
Some innovative maintenance managers have obtained good results in their experiments with larger bore OTR tire-type valves. This concept is logical but the problem of changing servicing equipment nationwide or carrying valve adapters have discouraged this approach.
Best results using standard equipment can be achieved by maintaining target pressures in delivery lines, having sufficient volume reserves to service maximum expected line drawdown, and eliminating restrictions in delivery lines. Some bead lubricants tend to dry or lose “slipperiness” faster than others, so the time interval between application and tire airing should be controlled.

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Clean Seats and Valves

Another area often overlooked is wheel bead seat cleanliness. Corrosion/oxidation and/or residue from certain types of bead lubricants are common causes of irregular seating that can prevent proper sealing at the tire/wheel interface.
Correct inflation pressure settings require good regulating equipment and frequent, regularly scheduled calibration using a high quality master gauge. These are available from local tire supply houses and every shop that services tires should have and use one. Once inflated, the annular opening between the valve core and housing must be kept clean to avoid leaks.
Metal sealing valve caps are normally recommended to protect the valve from the outside environment. Valves not properly protected from dirt, road chemicals, and other contaminants can sometimes become “leakers” during well-intentioned pressure checks.
One option is the use of flow-through valve extensions that provide a dirt seal, but these generally don’t provide the secondary pressure sealing insurance offered by a metal screw-on cap. If dry balancing materials are used inside the tire, filtered valve cores are highly recommended. These typically have fine screens fitted to the interior core end to prevent material contained in the tire cavity from entering the sealing area.

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TPMS Still Need Checks

On-board inflation maintenance systems have recently become available for trailer applications and are expected to follow for drive axle fitments in the next 12 to 18 months. These typically route compressed air, already dried for brake system use, from truck or trailer air tanks through the axle housing to tire valves at each axle end.
While these systems eliminate the need for time-consuming conventional pressure checks and address the goal of equalizing pressures in dual tire sets, care must be taken to monitor any make-up inflation required. Continuing inflation to a tire having, for example, a nail hole puncture will likely result in premature casing failure.
These basics are not all-inclusive but intended to highlight some features of successful tire programs. Major tire manufacturers have experienced consultants available to work with your servicing people for detailed training and to troubleshoot your particular operations.
Just ask for their help. 

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