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TIRE INFLATION
A tire's ability to carry weight and its heat-- building characteristics
are directly related to inflation pressure, and maintaining it is one
of the most important safety procedures on any RV owner's checklist.
The higher the pressure, the more weight the tire can support, up to,
but not exceeding, its maximum cold-inflation pressure listed on the
tire sidewall; the only exception is light-truck tires, which may be
inflated as much as 10 psi over the cold-inflation pressure listed
on the sidewall. Allow inflation pressure to drop, and the tire can
become dangerously overloaded, resulting in excessive heat buildup
and possibly resulting in a blowout. Even a short period of significant
underinflation can cause damage that is not immediately evident, but
which can result in destruction of the tire somewhere down the road.
Using the correct air pressure for the load also means a cooler-running,
longer-lasting trailer tire. Proper inflation assures best fuel-and-tire
mileage, not to mention overall handling. In fact, the Rubber Manufacturers
Association says that any tire run at less than 80 percent of the inflation
pressure required for a given load should be inspected for damage.
Tires that are not loaded to their maximums do not require maximum air
pressure, and load-inflation tables provide the values that can be used
to set air pressure for vehicles whose tire loads may be considerably
less than maximum — rear tires on lightly loaded pickup trucks,
for example. However, trailer weight does not fluctuate significantly
with variances in fresh and waste water and supplies, and trailer owners
should always inflate to the maximum pressure listed on the tire sidewall.
The inflation figures are for cold tires; if you check pressure after
the tire has been driven and thus warmed, you'll find it higher. This
pressure rise is normal and accounted for in the maximum cold-- pressure
rating.
INFLATION TOOLS
Adjusting tire pressure can take a few minutes, but it isn't difficult.
Having a small compressor at home is a help because the work can be
done at your leisure, when the tires are cold. If you must move the
trailer to a source of compressed air, the strictest definition of
a cold tire is one that has traveled a mile or less, or has cooled
for three to four hours. Ambient temperature is also a consideration
when setting tire pressures. A 10-degree-rise in ambient temperature
equates to a 1 psi change in tire pressure. Thus, if you set your tire
pressures on a cool 58-degree F spring day, they will magically rise
2 psi the following day should a weather front come through and pop
the temperature up to 78 F Dropping temperature lowers tire pressure
the same 1 psi per 10 degrees.
A very real variable is sunlight. Tires in the shade versus those sitting
in the sun can have definite pressure differences. Testing by a large
tire retailer has shown a 3 psi rise in tires left in the sun all day
versus those in the shade. This applies to shade versus sun sides of
the trailer, moving the trailer from a cool building into the warm sun
and so on. Clearly, setting pressures in even morning light and temperatures
simplifies the job.
An accurate pressure gauge is mandatory. Service station gauges found
on the end of air hoses are often inaccurate; the common pencil-type
gauge is a better choice. Better yet is a round-dial gauge with a short
length of hose. Coupled with its large, accurate and easy-to-read dials,
it makes measuring pressures much easier. A selection of air chucks may
also prove useful, depending on the style of valve stems on your wheels.
A visit to a local auto-supply store should net you the necessary air
chuck if the common acorn head won't work.
Because ambient temperature affects tire pressure and tires naturally
leak a little air - 1 to 2 psi a month is considered normal - it's important
to check tire pressures once a month. Weekly pressure checks are advisable
during trips, along with visual inspection every day.
Next - Tire Size
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