Newsletter No 45
November 2008
Partial first draft....
NITROGEN IN YOUR TIRES-JUST A BUNCH OF HOT AIR? (Forewarned is forearmed)(When wheel it ever end...)(Drawing a bead on excesses)
Recently
I have fielded a number of questions about filling tires with
nitrogen. It is the latest fad in tires, so you might have heard
of it. Typically you go to buy tires or have you car in for some
other service and you are told about the benefits of replacing the air
in you tires with pure nitrogen. Should you do it? Is it a
good idea? I have the answer in two forms, the short one and the
long one.
The short answer is "no, not worth the
cost". The long answer delves into why it is a waste of money for
most of us, but why it may work for some people.. If you don't
want to know why, you can skip to the next heading.
So, if race
cars and some airplanes use nitrogen in their tires, why shouldn't I
use it in my car? Good question. It will not harm you car,
only your wallet. The real harm I see in switching to pure
nitrogen instead of air is that it will give drivers a false sense of
security that their tires don't need to be checked. And, one of
the biggest problems I see with car maintenance is neglected tire
pressures, whether they are filled with nitrogen or air. Low tire
pressure can be expensive and dangerous. As the pressures gets
lower, the load carrying capacity of the tire diminishes. It can
drop below the point at which it cannot support the car any
longer. This may or may not be noticeable to the driver! It
can lead to loss of stability and hence, control. Low
pressure can also lead to sudden tire failure, I think we can all
agree that correct tire pressure is an important safety issue with
cars.
So, what is the deal with using nitrogen?
Why use it? The best reason for using pure nitrogen is that it
holds a more stable pressure no matter what the weather or how hot the
tires get from driving. Remember that you normally need to check
tire pressures when the tires are "cold", that is, not having been run
for a while. That is less important with a pure nitrogen
fill. This leads me to another reason that it may be harmful to
your wallet to buy nitrogen.
It is a well known fact
that if you raise tire pressures you get better fuel economy, due to
lowering the rolling resistance of the tires. For example, to
optimize fuel economy on my Prius, I run them at 44 psi. Toyota
recommends a much lower pressure around 30 psi. I can feel the
difference in how the car rolls, and can see higher fuel numbers on the
dash. Now, if nitrogen is more stable and the pressure does not
rise in a hot tire, the rolling resistance will be higher. Thus,
you will get WORSE fuel economy with a pure nitrogen fill! You
can compensate for this by filling the tires even higher, but how much?
When
I was a young man studying aerospace sciences, I ran around with
nitrogen in my tires (This was back in the seventies.) Did it
make any difference? You bet! I was COOL! I could
make all of my pilot buddies feel left out, because they just had plain
old air in their tires.
Point-counterpoint
Nitrogen filled tires don't have moisture in them. Air systems
used for filling tires professionally also use dried air.
Nitrogen filled tires have no oxygen inside them and therefore the
wheel can't corrode and the rubber tire cannot rot. Wheels and
tires don't corrode from the inside out. When dismounting an old
cracked tire, the insides are always clean and fresh, unlike the
exterior. I have never seen a tire replaced because of corrosion
or rubber deterioration from the inside out.
TIres hold their pressure longer than with plain air. The loss of
pressure is similar, and pressures should be checked periodically
regardless. See this test:
http://blogs.consumerreports.org/cars/2007/10/tires-nitrogen-.html
Nitrogen filled tires last longer. There is no evidence this is
true. TIres wear out at the same rate regardless of what is in
them.
In summary, there is no practical benefit to filling the tires
with nitrogen. The benefits are theoretical and very unlikely to
justify the cost.
Stop in to visit us, or if you have any questions about your cars, call us at 651-635-0395.
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