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2torial #0817:
Learn2 Improve Your Gas Mileage
(Continued)
 Maintain optimum tire pressure
It sounds like a no-brainer, but when was the last time that you
checked your tire pressure? It takes more effort for an engine to
propel an underinflated tire than a properly inflated one--the engine
uses more gas to move it along.
The trickiest part of checking your tire pressure is that you actually
have to check it twice: once before the vehicle has been moved that
day, and again when you're at a gas station with an air hose. The
first reading is from a cold tire, and it's the accurate one, while
the second is from a tire that has warmed up from rolling on the
pavement. The second reading will be a bit higher than the first.
Here's the routine:
- Get a good quality tire gauge, and measure the pressure
in all four tires before you move the vehicle. You'll do this
by removing the plastic caps on your valve stems and pressing
the gauge firmly down over the metal threads on the end of the
stem. You'll hear a little hiss as a bit of air escapes, but when
you press the gauge firmly down and hold it there, the noise will
stop and the gauge will register the tire pressure.
- Write down the measurement for each tire--this is your cold
measurement. Tire companies specifications reflect cold
tire pressures, and pressure is measured in PSI, or pounds
per square inch.
- The auto manufacturer has specified tire pressures for
both front and back tires. Look for these specs on the inside
edge of the driver's door, on the inside of the glove compartment
door, or in the owner's manual. Use these numbers, rather than
the numbers printed on the outside of the tire, to find out how
much pressure should be in the tires.
- Compare the cold measurements with the manufacturer's
pressure recommendations. If the manufacturer recommends a different
pressure (either higher or lower) than the cold measurement, you'll
adjust the tire pressure accordingly.
- Find a service station with an air hose. Sometimes you'll
need to put a coin in to make it work, but in most places there
won't be any charge. There will either be a metal handle that
releases air when you squeeze it, or a simple metal fitting that
releases air when it's pressed over the valve stem.
- Take the tire pressure again with your own tire gauge.
It'll probably be a bit higher than the cold measurement, since
the tire has warmed up from rolling along the pavement. This will
be the warm measurement.
- If the cold measurement was lower than the manufacturer's
recommendation, add the proper amount of air with the hose. How
much? Use the warm measurement as your guide. Let's say you compare
the cold measurement (say, 32 PSI) with the manufacturer's recommendation
(35 PSI)--the tire needs three more pounds of pressure. If the
warm measurement was 34 PSI, fill up the tire until the gauge
reads 37 PSI. Don't worry if the final measurement is more than
the manufacturer's recommendation--tomorrow morning, when the
tire is cold again, the pressure will be correct.
- On the other hand, if the cold measurement was higher
than the manufacturer's recommendation, release the excess pressure
from the tire. (This is easy to do: find the valve, and press
on the metal piece in the center of the valve with your fingernail,
a key, or a small stone, until your hear a hissing sound.) Again,
use the warm measurement as your guide. For example, if you knew
from your cold measurement that the tire had two pounds of excess
pressure, and the warm measurement is 38 PSI, release pressure
until the gauge reads 36 PSI.
- Tires lose pressure at different rates. If you measure
tire pressure every few weeks or so, you'll get a better idea
of how often adjustments are necessary. Don't try to go by the
tires appearance, as modern radial tires often look under inflated
when they're not.
- Overly inflated tires can wear unevenly, so don't try
to overinflate them into balloons.
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