Are You Ruining Your Tires With Compressed Air?Posted in How To: Wheels Tires on April 1, 2012
Nitrogen (N2) filled tires have long been a part of the commercial truck, racing, aircraft, military, and emergency vehicle realms. The benefits have lately begun trickling down to the general public as the technology becomes more affordable. With Parker’s new TyreSaver wand, individual owners now have practical access to Nitrogen for their wheeling or street vehicle. We recently had the chance to put this new product through its paces and look at N2-filled tires in general.
What is “Air”?
The air we breathe is made up of 78 percent nitrogen, 20 percent oxygen, and 2 percent water vapor in varying amounts and other things. If you own a compressor, you know draining water from the tank is a frequent maintenance task. Water condenses easily in the dense atmosphere of a 150-psi air tank and even more easily in your hoses and air tools as it’s being used, sometimes spraying lots of water from the exhaust. You don’t want that stuff in air tools or tires. Air line dryers and filters help but there is a limit to how dry you can make ordinary compressed air. What’s more, many compressors are often sadly neglected.
N2 vs. Air in Tires
Internal tire moisture has several detrimental effects, including internal rim corrosion. Corroded rims can weaken and fail over time but, even at a beginning level, it can cause bead and valve core leaks. Moisture in the tires also causes greater pressure fluctuations due to temperature. Nitrogen is almost totally devoid of moisture and that’s one reason racers use it. Race car handling is fine-tuned via tire pressure and only a few psi can alter a car’s handling characteristics. Nitrogen delivers predictable results based on temperature. On top of that, nitrogen-filled tires are much safer in a fire.
All tires lose pressure over time due to a process called permeation. Under pressure, air molecules work their way through the tire into the lower-pressure atmosphere via microscopic passages in the rubber. The NHTSA (National Highway Traffic Safety Administration) has quoted average losses of between 2 and 5 percent per month. According to tests done by Bridgestone/Firestone, dynamic losses are greater than static.
A tire filled with N2 will lose pressure at a much lower rate than shop air because the nitrogen molecules are individually larger. Quoted permeation rates are generally between 1 to 2 percent per month for N2, sometimes under 1 percent. Parker quotes figures of 38 percent less permeation with N2 versus compressed air in static situations and 55 percent slower in dynamic. Better tires have thicker, more dense inner liners that are less permeable, so there are different pressure loss rates across the range of tires available, regardless of air or N2 being in the tire.
Combined with heat, the permeation of oxygen and water molecules through the tire has deteriorating effects. On their way out, those elements reach the belts and plies, oxidation takes place and the tire gradually deteriorates from the inside out. For the average car and light truck driver, the tire is usually worn out normally before that’s an issue but a study done by Ford showed a tire with N2 aged less in two years than one filled with air for three weeks. Internal deterioration is more a problem in the big truck realm, where a tire carcass may be recapped several times.
Parker’s TyreSaver 3.0
The TyreSaver 3.0 is the smallest, least expensive nitrogen generator on the market and that puts N2 within reach of performance-oriented individuals in their home shops. The wand filters the air at a microscopic level, allowing the larger N2 molecules to pass but the oxygen and water molecules to exit thru vents. The result is 95 percent pure N2.
While we trust the many independent studies on the benefits of N2 in tires, we looked for some objective way to test the claims ourselves in a short period of time. We decided to test pressure change from temperature by filling one tire at each end with N2 and other with shop air. Pressure was set at 70 degrees in the shop to 42 psi up front and 44 in back. The standard pressure rise, or drop, is 1 psi per 10 degrees of air temperature for dry air or N2 but pressure change increases with more water vapor in the air. We then went for a 70-mile freeway jaunt on a 65-degree fall day.
The front tire with N2 showed 3 psi less (43 versus 46) than the tire with shop air at the test temperature. In back, the N2 tire was also 3 psi less (45 versus 48). These differences illustrate the effects of moisture in the tires but pressure rise hot is not as important as pressure drop cold. That’s the direction that decreases fuel economy and increases tire wear. Frequent tire pressure maintenance can alleviate all the bad effects, but statistics show most people aren’t nearly diligent enough. Nitrogen makes the tire a bit more forgiving to neglect.
Weighing the Technology
There really are no cons to using N2 in and of itself. It’s proven to work as advertised. The issues come with balancing the costs versus the benefits because it isn’t dirt cheap or available at every corner. The numbers crunch well in commercial truck fleets and the safety benefits dictate N2 use in aircraft and military venues. Racers need it for the tuning aspects and safety. For the average private owner, the numbers may not add up as well.
Though only a fraction the cost of big N2 generators, the TyreSaver 3.0 is still not cheap and it’s mostly marketed to the retail environment. Expect to pay around a grand for one. With 12,000 fills, that’s about $0.08 per fill, or $0.16 per purge and fill, which sounds better. Performance enthusiasts are usually willing to pay a premium, usually between $4 and $10 per tire at the increasing numbers of shops with the equipment, though sometimes you can get it included with new tires. Individuals with private fleets may find the TyreSaver a more appealing expense than a common individual. N2 works just as well in motorcycle, ATV, and trailer tires. Only you can decide the costs versus the benefits, but we are satisfied that the technology and the benefits of having N2 in your tires are the real deal.
Cartridge capacity: Approximately 12,000 tire fills
Max tire pressure (psi): 80 (160 input)
N2 purity: 95% average
Ambient temperature range (F): -4 to +122
Weight (lbs): 2.6
Length (in): 25.2