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As if the tangled task of maintaining your vehicle without draining
your bank account isn't tough enough, some of the folks who sell and service the
tires on your car have come up with another item for your consideration:
Would you like regular air or nitrogen with your
tires? Nitrogen? OK, expect to be charged
as much as $10 per tire for that choice. Is it worth it? Let's
check the basics.
You might trace this latest kink
to the concerns of several years ago about blowouts
on SUVs, particularly the Ford Explorer equipped
with Firestone tires. What's at issue with nitrogen
versus plain old air, which comes from the pump
at the gas station, is that nitrogen is a dryer,
more stable gas that's less prone to changes in
pressure due to heat or cold.
Nitrogen has long been used in aircraft
tires and in the tires of race cars. Its use in
average road cars is new and controversial.
Proponents of
nitrogen argue that since studies show that fewer than 60 percent of drivers rarely
if ever check the inflation of their tires, anything that will slow the normal
leakage -- estimated by some at 1 to 2 pounds per square inch a month -- is a
good safety measure. One Web site that lays out the claims
for using nitrogen is www.getnitrogen.org. It
says, essentially, that putting nitrogen in your tires will increase your fuel
efficiency because properly inflated tires will reduce rolling resistance, which
can mean as much as a 3 percent better mileage than a car with under-inflated
tires. It also claims that nitrogen will not degrade the interior
rubber of the tire or corrode the wheels, since it contains no oxygen or water
vapor -- both present in the atmosphere we breathe and pump into our tires. But
a closer examination of the facts makes some of the claims for nitrogen seem at
best anecdotal or illusory for everyday drivers. First, the
air around us is already 78 percent nitrogen, with 21 percent oxygen and 1 percent
other gases. So going to pure nitrogen only squeezes out a small amount of the
oxygen molecules that nitrogen proponents argue are so detrimental. Also,
the advantage of nitrogen being more stable and less prone to changes in pressure
due to heat in the tires seems of little benefit to average drivers. Race teams
use it because they can change the handling of the car by adjusting individual
tire pressure by as little as a quarter pound. So having a gas that's ultra stable
has real benefits when dealing with such small degrees. Nitrogen
proponents say that the nature of the gas means it's less prone to leaking out
over time through the pores present in rubber tires. But most air leakage in tires
can be traced to poor fit around the rim of the wheel or the valve stem, rather
than gas permeating through the rubber. Claims of nitrogen
being more friendly to the rubber and wheels is also questionable, since most
tires wear out the tread on the outside long before the inner rubber would go
bad from exposure to oxygen. The same factors hold true for wheels, many of which
are made from alloys, not straight steel. You're far more likely to damage a wheel
from hitting a curb than see a wheel go bad from oxidation. A
good site that takes a contrarian point of view on nitrogen in passenger car tires
is www.eng-tips.com, which
is run by engineers. When it comes down to a dollar decision,
it's hard to argue that spending as much as $40 for nitrogen in a set of tires
is a good fiscal move. Even if you accept the arguments of
proponents, at some point you are going to have to add air to your tires -- not
even the most ardent nitrogen pushers will say that your tires will never lose
pressure. When that happens, you're most likely to go to the corner gas station,
put in a couple of quarters and pump your tire up with regular old air, which
will mix with the nitrogen and degrade its benefits. Save your
money and just keep an eye on your tire pressures.
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