Why Inflating Tires With Nitrogen Makes Sense
From: Tire Retread Information Bureau
The practice of inflating tires with nitrogen has been around for a long
time. Because of the benefits of nitrogen over air, is has been commonly
used in tires on aerospace vehicles, commercial and military aircraft,
racecars and off-road equipment.
With advances in technology and the expanding commercial infrastructure
of nitrogen availability, nitrogen inflation is a growing trend in the
transportation industry.
This article by the Tire Retread Information Bureau (TRIB), provides a
primer and overview of nitrogen inflation, and discusses how it helps
optimize tire costs while providing environmental benefits.
TRIB is a non-profit, member-supported industry association dedicated
to the recycling of tires through retreading and repairing, and to
promoting proper tire maintenance for all tires.
By far, the single most critical factor for maximizing tire life and
minimizing the chance of catastrophic tire failure is maintaining the
proper inflation pressure for a given tire size and load. Properly
inflated tires not only last longer, but also are safer.
One way to help maintain proper tire inflation is to fill tires with
nitrogen instead of compressed air. Nitrogen allows a tire to retain more
of its original properties.
Among the benefits of nitrogen inflation: less inflation pressure loss
for a more stable, consistent tire pressure; cooler running tires; longer
tread life; less oxidation of tire components, and reduced rim and wheel
corrosion. The result is increased tire life, improved fuel economy,
reduced tire aging and a more durable casing for improved retreadability.
While the trend toward nitrogen inflation is relatively “new” to the
truck and bus tire market, it has been long used in tires on Formula One,
Indy, Le Mans and NASCAR racecars; commercial and military aircraft;
military vehicles; heavy off-road construction equipment, and the Space
Shuttle. The Moon Buggy had its tires inflated with nitrogen. Also, the
Tour de France bikes use nitrogen in their tires. Nitrogen is
environmentally safe and non-combustible.
A reason for the slow growth of nitrogen tire inflation in on-highway
transportation has been the availability of nitrogen. However, more and
more nitrogen filling facilities are appearing nationwide as on-site
nitrogen generators have become more affordable and as more manufacturers
of nitrogen generators have entered the marketplace.
THE SCIENCE
Over time the pressurized air inside a tire slowly migrates and permeates
its way into and through the tire. Air contains moisture. So in addition
to reducing the tire’s inflation pressure, the oxygen and moisture in the
air reacts with the rubber compounds in the tire, causing them to break
down and lose their strength and durability. A chart is available
illustrating that nitrogen is the slowest of all gases to flow through a
permeable barrier such as a tire. For a copy of the chart please contact
us at the number or email address shown below.
An underinflated tire is much more prone to premature failures. That’s
because when underinflated, as a tire rolls, it flexes more than it was
designed to. This flexing bends the tire’s rubber and steel (used within
the rubber to provide additional operating characteristics) and generates
heat. Heat is a tire’s worst enemy and accelerates tire wear dramatically.
There is a direct correlation between how much a tire is underinflated and
how much faster it wears.
Since air, which contains oxygen, is not an inert gas, it is affected
by changes in temperature, which affects the rate of air loss from a tire.
The air inside a tire expands when heated and contracts when cooled. More
air is lost in hot weather. The consensus is that for every 10-degree
Fahrenheit change in temperature, there will be a one psi (pound per
square inch) change in the pressure of a tire. Nitrogen will not
fluctuate as much. Being an inert gas - not readily changed by chemical
reaction, nitrogen provides constant pressure and is less susceptible to
accelerated diffusion caused by changing temperatures.
Nitrogen inflation minimizes moisture and oxygen in a tire so there is
less rubber degradation and no corrosive properties as found in compressed
air. A reduction in rubber oxidation slows a tire’s “aging,” improving the
casing’s structural durability, lengthening its useful life and yielding a
higher proportion of retreadable casings that can survive more retread
cycles. All of this helps lower operating costs. Some fleet managers, who
had been dead set against retreads, are now willing to use retreads with
nitrogen inflation.
Because nitrogen molecules are slightly larger and less permeable than
oxygen and all the other gases in air, it migrates considerably slower
through a tire. It might take a truck or bus tire inflated with nitrogen
about three months to lose two psi, whereas even a well-maintained tire
inflated with compressed air will lose, on average, about two psi per
month.
INFLATION CHECKS
Just because nitrogen provides consistent inflation pressure over longer
periods, that doesn’t mean there is no longer a need to regularly and
properly check tire pressure. Tires still need to be checked using a
calibrated tire gauge and when a tire is “cold” - meaning when a tire is
at approximately the same temperature as the surrounding air, typically
before a vehicle has been driven, or driven less than one mile.
Kicking or thumping a tire cannot accurately estimate inflation
pressure. Trying to determine if a tire needs air by thumping it is as
effective as trying to determine if a vehicle’s engine needs oil by
thumping on its hood.
Regardless of what is inside a tire - air or nitrogen, properly
maintaining tires maximizes tire life and fuel economy, and provides
improved handling, traction, braking and load-carrying capability. By
being more fuel efficient, less fuel is consumed, which decreases
petroleum fuel demand and reduces emissions and pollution.
ENVIRONMENTAL BENEFITS
Nitrogen can provide stronger casings for more retreadability, and
retreaded tires actively contribute to helping conserve valuable finite
natural resources and reduce solid waste disposal problems. Every retread
produced means one less new tire, which minimizes the number of new tires
that need to be produced annually.
Production of new truck and bus tires consumes large amounts of energy
and materials that impact the environment. Truck and bus tires are
basically petrochemical products. It takes 22 gallons of oil to
manufacture one new tire. Most of that oil is used in the tire casing,
which is reused in the retreading process, where only approximately 7
gallons of oil is required to retread that same tire. So each time a tire
is retreaded, approximately 15 gallons of oil are saved.
Retreading conserves hundreds of millions of gallons of oil every year,
which in today’s oil-scarce world is extremely important. And because
retreading requires less rubber, fewer rubber trees are “tapped,” which
helps preserve the natural environment and reduces the loss of natural
habitat.
To make the crude rubber used to manufacture tire, workers known as
“tappers” make a shallow cut in the trunk of rubber trees and insert a
“tap” - actually as small spout - with a cup underneath. Latex containing
rubber drips into the cup. The latex is collected and processed into crude
rubber.
By extending the useful life of a tire, retreading offers additional
environmental benefits. Every tire retreaded is a tire that does not need
to be disposed of.
Because every reputable truck and bus tire manufacturer designs and
engineers its tires for several retreading lives, only one worn tire
casing requires disposal instead of many. The natural resources that are
saved and the positive impact on the environment are multiplied.
So are the cost benefits to users of retreaded tries. For most
commercial vehicle fleets, tires represent the third largest item in their
operating budget after labor and fuel costs. Retreading can cut tire costs
in half and sometimes even more.
MIXING NITROGEN & AIR
There is some confusion about what happens when nitrogen and air are mixed
inside a tire. By way of example: when a nitrogen-inflated tire needs some
additional pressure and nitrogen is not available.
Normal air is about 78% nitrogen; so adding compressed air will simply
drop the nitrogen purity. There shouldn’t be any adverse affects on the
tire or vehicle handling, provided the pressure is kept at the proper
level.
The manufacturers of nitrogen inflation system advise that any tire
containing both nitrogen and air be purged and then re-inflated with the
proper amount of nitrogen as soon as possible. The same procedure holds
true in the event that a tire would need to be replaced and nitrogen is
not available.
In a situation where a nitrogen-inflated steer tire has been repaired
and refilled with air, some nitrogen inflation system manufacturers
recommend that the nitrogen be let out of the other steer tire and
re-filled with air.
The reason, they explain, is that an air-filled tire will heat up and
expand, whereas the tire with nitrogen will not, possibly causing a slight
pull to the side with the nitrogen-inflated tire. With air in both steer
tires, the air pressure will expand relatively equally, so there shouldn’t
be any steering issues.
Here again, as soon as possible, the air should be purged from both
steer tires and properly re-inflated with nitrogen. There is a small
controversy over this point. There are some in the field who believe the
effect of topping up nitrogen filled tire with air has too small an effect
in handling terms to require such action.
For additional information, including a list of locations where
nitrogen is available, contact the Tire Retread Information Bureau (TRIB)
toll free from anywhere in North America at (888) 473-8732, send an e-mail
to info@retread.org or visit TRIB’s website at www.retread.org.
TRIB WISHES TO THANK OUR MEMBERS WHO DEAL WITH NITROGEN
FOR CONTRIBUTING TO THIS ARTICLE.
Bibliography and Selected Reading
1. Airworthiness Standards: Transport Category Airplanes, 14CFR part
25.733, U.S. Code of Federal Regulations.
http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=36428fa124d2c4da59c6b875c89fac1c&rgn=div8&view=text&node=14:1.0.1.3.10.4.175.36&idno=14
2. Lawrence R. Sperberg, Million Mile Truck Tires – Available Today,
Stronger Longer Tires of El Paso, Inc. El Paso, TX 1985.
3. Shell Unveils Nitrogen Tire-Inflation Systems, Associated Press,
Houston, July 3, 1997.
4. Haray, K and Sun-Tak Hwang, Permeation of oxygen, argon and nitrogen
through polymer membranes, Journal of Membrane Science, 71, (1992) 13-27.
5. Peacock, R.N., Practical selection of elastomer materials for vacuum
seals, J. Vac. Sci. Technol. 17(1) Jan/Feb 1980.
6. Technical Information, Tire Inspection: Bridgestone/Firestone http://www.trucktires.com/us_eng/technical/bftechnical/tire_inspection_b.asp
7. Garrot, W. Riley; What Applied Research has Learned from Industry About
Tire Aging, NHTSA, 5/2003. http://www-nrd.nhtsa.dot.gov/vrtc/ca/tireaginglessons.pdf
8. Power, Stephen, Aeppel, Timothy; Many Current Models of Tires Don’t
Meet New Federal Rules,The Wall Street Journal, September 5th, 2002.
9. Baldwin, J.M., Bauer, David R., and Ellwood, Kevin R., Effects of
Nitrogen Inflation on Tire Aging and Performance, Rubber & Plastics News,
Vol. 34, No. 4, pp 14-19, 2004.
10. Tokita, N. et al., Uniroyal, Inc; Long Term Durability of Tires,
International Rubber Conference, Kyoto, Japan, October 1985.
11. Use of Nitrogen, Technical Bulletin PM-03-05, Michelin, Greenville,
SC, November, 2003.
12. Use of Nitrogen as Inflation Agent for Tires, Product Service Bulletin
#2004-09, Goodyear Tire and Rubber Company, Akron, OH, June 14, 2004.
13. Fisher, Peggy, 1998 Tire Debris Survey Summary , The Maintenance
Council of the American Trucking Association, 1998.
14. Walenga, Guy. Bridgestone/Firestone, Nitrogen Inflation for Truck
Tires. Clemson Tire Conference. Clemson University, 11 Mar. 2004.
15. Fisher, Peggy, A New Gas for the New Millenium? , Tire Business,
7/2000.
16. G. Potts, et al., Technical Trends in Indoor Tire Testing, Rubber
Division, American Chemical Society, Cleveland, OH, 10/2003.
17. The ‘Mephitic Air’ Advantage , Automotive Design and Production, pg
34, February, 2003.
18. Gerard-O’Connell, Mark Cool Running. Fleet Maintenance, pg 14,
October, 2003.
19. Bridgestone/Firestone Annual Report http://www.bridgestone.co.jp/english/info/profile/pdf/07.pdf
http://www.bridgestone.co.jp/ir/ar/2000/05japan.html
20. Should You Stop Putting Air in Your Tires, Real Questions, Real
Answers, Bridgestone/Firestone North America, LLC, Vol. 8, Issue 3, 2003.
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