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.