Alternate inflation

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A problem with nitrogen inflation is adding air on the road, which compromises the benefits. Proponents of nitrogen envision machines like this at truck stops and service stations.

The advantages of nitrogen tire inflation have been understood for many years. But there remains much debate as to the magnitude of those advantages, and as to whether filling up with the gas can provide a return on investment.

Different behavior and performance
Proponents of nitrogen will tell you that the gas has larger molecules than air, so migration through rubber is slower, and tires stay properly inflated longer. They also correctly note that nitrogen is drier than air, so corrosive moisture is reduced. And since moisture holds heat, a dry tire should run cooler.

Finally, nitrogen doesn’t expand and contract, or vary as much in temperature as air, so it’s argued that tires maintain a more consistent footprint, thus improving wear.

The pros
In a previous position as president of Roadway Tire Co., Peggy Fisher, now president of TireStamp, was keenly interested in nitrogen inflation for the reasons noted above. “A nitrogen-filled tire will lose only about 2 psi over six months, as opposed to losing that amount in two months using air,” Fisher says. “Also, the moisture in air can attack a tire’s belts as it passes through, causing the casing to lose retreadability.” Moisture in air also can attack wheels, creating small particles that can lodge in valve seats when a tire is aired or gauged, she says.

The problem Fisher experienced was that nitrogen generators were very large and extremely expensive. “They were almost the size of a small house,” she recalls. “If I’d had today’s technology, I definitely would have tried it.” With today’s smaller, more affordable generators, testing to prove nitrogen’s benefits now is feasible, she says. If in her old position today, “I’d be doing it.”

The caveats
To enjoy the full benefits of nitrogen, it has to be pure, according to Asa Sharp, OEM and national account executive for International Marketing. “Tests have shown that you need 95 percent nitrogen in a tire,” Sharp says. The problem, he says, is make-up air on the road, where nitrogen probably won’t be available. “You can negate the benefits with as little as 10 percent air,” he says.

Moreover, Sharp doesn’t believe reduced sidewall permeation is as important as it was 15 or 20 years ago. “Over the years, tire manufacturers have upgraded air retention through the use of barrier liners and new bonding techniques,” he says.

Tim Miller, marketing communications manager for Goodyear Tire and Rubber, agrees that the biggest problem with nitrogen is make-up air. “It defeats the purpose,” he says. And as for nitrogen’s absence of moisture, “I think you can get the same benefit by using dry air.”

That requires only the addition of an air dryer to a dedicated airing line, Miller says.

Using an air dryer would be better, agrees Guy Walenga, engineering manager for Bridgestone Firestone North America. “We did a study on the age of tire casings, and found some up to 14 years old,” Walenga says. “Maybe they could last longer with nitrogen, but how much?”

As far as seepage is concerned, nitrogen can offer some benefit, Walenga admits. “Planes, racecars and mining equipment are good candidates because they have their own local facilities and don’t have to depend on outside sources,” he says. But for truck tires, “We neither encourage nor discourage nitrogen use.”

Thanks to better inner liner compounds, today’s tires don’t lose that much air over a period of time, says Al Cohn, director of new markets and support engineering for Pressure Systems International. Air permeation isn’t the leading cause of underinflation anyway, according to Cohn: Punctures and leaky valve stems are far more common instigators.

“Nitrogen is of particular value for earth movers,” Cohn says, “because they use electro-brakes that generate a lot of heat, and nitrogen is fire-resistant.”

Regarding nitrogen’s reduced expansion and contraction, Michael Burroughes, product manager for Michelin Americas Truck Tires, notes that “Our tires are designed to operate with air. They reach a thermal equilibrium – an ideal marriage of temperature and pressure. Nitrogen can alter that optimization.” However, its use won’t void the company’s warranty, Burroughes says.

A more subtle risk, he adds, is the perception that using nitrogen means that tire pressure doesn’t have to be checked. “You can’t neglect proper maintenance,” Burroughes says. “And checking pressure provides an opportunity to visually inspect tires.”

Curtis Decker, Continental’s field engineering manager, says his company will support any efforts by its customers to maintain proper inflation pressure. “But you need to look at the nitrogen infrastructure where you operate,” Decker says. “If you have hubs that can handle nitrogen inflation, fine. But if not, airing-up on the road will compromise the benefits.”

Cost vs. benefit
TireStamp’s Fisher knows one fleet using nitrogen, reportedly with great success. “The fleet manager reports better treadwear and reduced tire failures,” she says. He’s getting better fuel economy, and his tire costs have fallen from $7,500 to $3,500 per month, Fisher says.

But such reports usually are short-term and largely anecdotal. “No one’s been using nitrogen for very long, so good data is hard to come by,” Fisher says.

Decker says Continental has one customer who just had a nitrogen generator installed in one of his shops. “It cost him $6,200 installed, and it has all the capacity he needs,” he says. But is it worth it? “Fleets have to make that determination on their individual circumstances.”

Neil Brensinger, owner and maintenance manager for Service Truck Line, based in Schuylkill County, Pa., says his tire supplier has assured him that the claimed benefits of nitrogen are true. “But I know if you add regular air on the road, you lose those benefits,” Brensinger says. Then there’s the question of buying a nitrogen generator. “They’re expensive,” he says, “and I’m not sure if there’s a return on the investment.”

Cohn says PSI hasn’t seen any data to support claims of benefits. “It seems hard to justify the cost,” he says. “If fleets are interested, I would suggest they run their own tests.”
Michelin’s Burroughes agrees. “There isn’t any cost/benefit data,” he says. “Interested fleets need to experiment.”

To be practical, “it must have a payback,” says Bridgestone Firestone’s Walenga. “As the product matures, it may well prove worthwhile.”

The good news is that using nitrogen can’t do any harm. “There are no negatives except cost,” says Fisher. “But if you use it and keep track of your tires, I think you’ll see improved mileage and better wear. You just need to determine if it’s worth it.”

Generating nitrogen
Once huge in size and cost, nitrogen generators today can be as compact as small tool chests. Made by such companies as Parker Hannifin, Ingersoll-Rand, Champion Pneumatic, Kreska and Branick, they can be free-standing, wall-mounted, rollable or even truck-mounted and completely mobile.

They work by moving ambient air – which is more than 78 percent nitrogen – through one or more semi-permeable membranes, which extract the nitrogen and move it to one or more storage tanks. Generally, they can be connected to an existing air system, or they can use a separate dedicated system. Nitrogen output can range from less than 2 to about 34 CFM.