Nitrogen Tire Inflation: Hot Stuff or Hot air?

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Most truck tires are inflated with air, which is 78% nitrogen. Equipment that extracts nitrogen from the air pumps about 95% pure, dry nitrogen into tires, increasing the nitrogen level to about 93%, or less. Proponents claim many advantages.

First, their case against air: More often than not, air contains lots of rust-causing moisture. Moisture retains heat and expands in hot driving conditions, causing over-inflation and reduced tire life. Oxygen molecules permeating the inner liner degrade the rubber and rust tire wall cords. As oxygen escapes, tires pressure falls, shortening tire life.

Their case for nitrogen: Rust is a non-issue with nitrogen. Even in hot conditions tire pressure barely rises above the cold-inflation pressure, to about 106 psi, according to one report, compared to 130-plus psi for air. Nitrogen molecules, bigger than oxygen molecules, do not permeate inner liners; rubber does not deteriorate as quickly and tires maintain pressure longer. Casings last longer and tolerate more retreads. Properly-inflated tires have less rolling resistance, improving fuel mileage.

Primary research documents and raw data are difficult to access, forcing casual researchers to rely on often selective summaries of what may or may not be solid research. So, for example, an August, 2005 document released by the Tire Retread Information Bureau (TRIB) refers to the nitrogen arguments as “The Science” and supports them. But without access to primary sources, it is impossible to know whether TRIB’s holus bolus support is justified.

Too, the evident cherry-picking of text to support nitrogen use is troubling. An 18-page presentation by the Ford Motor Company at a meeting of the Rubber Division, American Chemical Society in 2004 says in its abstract, “When nitrogen is used as the inflation media [sic], the change in rubber properties is significantly slowed down or even halted.” Yet a closer reading uncovers a more tentative conclusion and more questions; e.g., is oxidation occurring from the outside of the tire; what would be the magnitude of improvement due to nitrogen if the test had been done at a tire’s normal operating temperature and not at the 60C in an oven?

To claim that this Ford study is a categorical endorsement of nitrogen inflation would be a misrepresentation.

In section five of a larger Goodyear document, apparently dating from 2003, Goodyear discusses inflation. “At the present time, Goodyear endorses nitrogen inflation for certain sizes of earthmover tires used in particular applications…” Nitrogen proponents have jumped on such statements as good for the goose, good for the gander-style proof that nitrogen should be used in truck tires, but is that justified? Acknowledging that little controlled test data exists, Goodyear notes, “we know of no significantly improved casing durability or retread durability performance to be expected from nitrogen inflation in over-the-road truck tires.”

Bridgestone has determined that there are definite benefits to using nitrogen in maintaining casing integrity, but has not concluded that fleets will get more retreads from their casings, cautions Greg McDonald, with Bridgestone Engineering in Nashville. “Will fleets’ bottom lines be affected? Unknown.”

A National Highway Traffic Safety Administration (NHTSA) presentation from 2003 states that tire aging, due to heat and oxygen interactions, matters. High ambient temperatures result in more failures, and accelerate the rate of chemical aging. Although this information is referenced in other articles to bolster the claim that nitrogen-filled tires will endure fewer such indignities, the NHTSA presentation makes no such claim.

Bandag surely knows a thing or two about retreading truck tires, but the company’s Don Schauer says, “We really don’t have a position on the use of nitrogen for truck tire inflation.”

Nitrogen proponents like to refer to sources that admonish tire users to discard their tires after just a few years (six is a popular age), making what they see as a logical leap between oxygen-caused degradation, its removal and the consequent benefits of nitrogen. Yet one Bandag document “Making the Right Casing Utilisation Decisions” notes that some fleets are running casings 13-16 years old, while others seek to reduce tire failures by putting a three to four-year age limit on them. The document suggests that five to six years might make more sense from a return on investment point of view, but it does not advocate discarding tires at that age.

Adrian Leu, technical services manager for Eastern Canada, Yokohama Tire (Canada), says the theory behind the nitrogen inflation case makes sense. “Normally we do support the idea and agree with it. We are doing some follow-up tests (we have installed some sets of tires on some fleet trucks) to see to what extent we can see improvements on the maintenance side.”

Leu notes, “In a truck tire, premature aging due to oxygen will appear in about 10 years. Normally the oxygen, as it is, does not cause a big problem,” However, Yokohama officially supports the reduced-oxidation claim. The bulk of its support though, is for the benefits that flow from running with properly-inflated tires because nitrogen stabilizes tire pressure.

A Goodyear product service bulletin issued in 2004 states, “Goodyear supports the use of nitrogen, as an inflation gas … based on the ability for a tire to retain pressure for a longer period of time.” A 2003 Michelin Americas Small Tires (MAST) technical bulletin says the same thing. But Ralph Beaveridge, marketing manager, Michelin North America, is uncomfortable applying that assertion to truck tires.

Michelin’s technical people do not have the data to support any possible advantages of using nitrogen in truck tires, according to Beaveridge, and they are not encouraging the use of nitrogen, specifically. “Our tires,” Beaveridge says, “are designed to live in the North American marketplace where they are inflated with air. They are designed to operate overinflated [after they warm up]. The tires are designed for changes in temperature.”

Amid the claims and snorts, several Canadian fleets, and a nitrogen generating equipment manufacturer, are running trials to collect data and evaluate the promised benefits of inflating truck tires with nitrogen.

Quebec’s Groupe Robert is partway through an eight-month trial involving about 400 nitrogen-filled tires. Why? Rolling resistance and fuel consumption. “The price of fuel is enough to have us in nitrogen testing,” says tire manager Francois Gareau.

“Any modification in rolling resistance is critical. Only 2% reduction in rolling resistance is good enough.” [to justify the cost of nitrogen inflation],” Lue notes.

Paul Hamm, fleet maintenance manager with Winnipeg Motor Express, says, “When I take delivery of new equipment, or when I have new tires installed on a new tractor or trailer, I order nitrogen-filled tires as much as possible. I’ve had trailers go a whole year and lose only two pounds. That is unusual. My tire costs are far more consistent now and going down. I’m confident that a portion of that is attributable to nitrogen.”

On the other hand, Ken Price, corporate director of fleet services with Saskatoon-based Siemens Transportation Group, says, “I looked at it and it didn’t make any sense to me. We elected not to pursue it.”

The Drexan Corporation, in Burnaby, BC, which supplies nitrogen-inflation equipment to industry, is heading a six-month, $140,000 trial to quantify the benefits of nitrogen for long-haul trucking. The subject fleet, Harris Transport of Winnipeg, began converting (minus control groups) to nitrogen-inflated tires this April. The trial will track fuel consumption and tire wear; Transport Canada has agreed to refund up to 50% of the trial costs.

While the industry blows billions out their exhaust pipes, maybe Hamm has the best argument of the day: “You know, for five dollars a tire, I’m willing to take that risk. It is cheap.”

Carroll McCormick
is an award-winning writer who has been covering transportation industry issues and technologies for more than a decade. He is based in Quebec.

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