The Washington times., 1913-07-12
EXPERIMENTS PROVE
OLD THEORY WRONG
Air Pressure in Motor Tire Is
Not Increased During Heat
of Summer.
By F. l. REYNOLDS.

Quite often you read in Iour paper
of some new and wonderful discovery
made by science. You are not startled.
because man has grown accustomed
to the rapid advance of science. You
take the new discovery as IA matter OF
course. You adjust your ways OF HV-
ing TO fit the new discovery and pass 1t
by as you would a birthday-somethins
that time is sure to bring.
1t will be no surprise to motorists
to learn that science has again come
TO their rescue-this time discardlng
one of the long cherished theories re-
gard!ng tires.
Since the time the first pneumatic
sixteen years ago. by the Diamond
Rubber Company. II has been the pop
ular belief among motorists that the
air pressure in an automobile tire IN
creases greatly on hot daJ. ActinG
upon this misaprehension many mo-
torists are accustmoed to running their
tires at low pressure, at times even
Debating them, during the hot summer
seasons Experiments conducted by
the engineering staff Of the Diamond
Rubber Company recently. proved con-
clusively that increased pressure IN an
automobile tire, due to the heating cf
the tire. is less on hot day than on
a cold day.
Experiments Refute Theory.
These experiments were worked out
on the basis of the proved theory that
the absolute air pressure in any con-
tainer such as a tire, the volume OF
which remains constant, is in direct
to the absolute temperature.
The absolute pressure is obtained by
adding the atmospheric pressure OF III
pounds per square inch to the gauge
pressure. In order to obtain the aoso-
lutte temperature add 400 degrees to the
Fahrenheit, 460 degrees be-
ing what is known as the absolute zero.
Applying this rule, a formula can De
worked out which will give the flnai
pressure due to increase In temperature
in the tire when running.
Actual tests show that "a by tire
inflated to a pressure of y pounds per
square inch and run 25 miles in an hour
under average conditions on day when
the thermometer stands at rreezinS ID
degrees Fahrenheit). the temperature
will increase IS degrees. But on a day
when the thermometer is at the mean
(62 degrees Fahrenhei)'
and the same "a by ! tire is given Inc
a hove test of 25 miles in one hour. theh
the increase in temperature OF the ure
will be "a degrees.
Heat Reduces Pressure.
The experiments showed the final
pressure in the tire to be ISL pounds per
square inch. and the final temperature
to be g. degrees when the thermometer
stood at 81 degrees. an increase OF 81
pounds per square inch. When the
stood at 60 degrees the
final temperature was Sc degrees In
the tire and the pressure was U.b
pounds, an increase of SO pounds per
square inch When the thermometer
stood at 80 degrees the final temperature
in the tire was 123 degrees and the
pressure was only ~ pounds, an in
crease of 81 pounds per square inch.
AS a matter of fact. the increase in
pressure would be slightly less than
those noted above, due to a slightly
greater expansion of the tire itself.
caused by the greater pressures.
OF course. this heating OF tire Ia
injurious to It, but whenever the pres
sure in a tire is decreased, the heating
of the tire Is Increased rather than de-
,reased on account OF the greater bend
ng of the tire and consequent greater
friction and generation OF heat.
From the above II should be clear that |
he pressure in a tire should not be |
decreased on a hot day. as is commonly |
supposed, for the simple reason that It |
: impossible TO obtain an increase In !
he pressure, due to the heating of the |
ire in service sufficient to in any way |
njure II.