TIRES, TUBES, AND RIMS
TIRES.--Three kinds of tires are now used, namely: Solid, cushion,
and pneumatic. These forms all use rubber, or some compound with
the qualities and characteristics of rubber, so as to afford a good
tractive surface, as well as resiliency.
[Illustration: Fig. 11. Solid Tire.]
_The solid_ tires are used on heavy trucks, where weight and not speed
must be provided for.
_Cushion_ tires are sometimes employed on cars and trucks of medium
weight.
_Pneumatic_ tires, in which air is used, are universally used in
automobiles for all other purposes.
[Illustration: Fig. 12. Single Tube.]
The air is confined in two ways:
First, by what is known as the “single tube.” (Fig. 12.)
Second, by the “double,” or inner tube system. (Fig. 13.)
The single tube is well adapted for light vehicles, or where great
speed or weight are not considered, and this type is now confined to
bicycles. But it has certain disadvantages, namely: That of creeping,
due to the impossibility of properly securing it to the rim of the
wheel. Sand and grit are also liable to creep in between the tire and
rim, and wear the material, thereby ruining it.
The outer casing, or shoe, is split on its inner side, and usually
provided with an annular flange on each side of the split, which rests
against the rim of the wheel, and is adapted to receive a rim which
securely fastens the annular flange of the shoe, to the rim of the
wheel.
[Illustration: Fig. 13. Double Tube.]
Various ways are provided for holding the shoe to the rim of the wheel;
but in the different types shown by the illustrations, Figs. 13 and 14,
the shoe has a flange which is held within channels on the rim, or by
some form of fastening device.
_The inner_ tube is usually of thin elastic rubber, so made that when
properly inflated it will fit the outer tube or casing. The outer
part, which can be made of a different rubber compound, and is better
adapted to stand wear, whereas, the inner tube, which is made of the
best, and more costly material is protected.
ADVANTAGE OF DOUBLE TUBE.--The great advantage of the double tube is
due to the positive means of fastening it to the rim of the wheel, so
as to prevent creeping.
In the single tire construction the latter is liable to roll out of its
bed where quick turns are made, but with the double tube this is not
possible.
[Illustration: Fig. 14. Illustrating Tire-removing Tool.]
PUTTING ON AND TAKING OFF DOUBLE TUBES.--To do this properly with
clincher tires is quite an art. A pair of blunt, round-ended levers is
best for the purpose.
The practice is to use cold chisels, screw drivers and like sharp or
pointed tools. This is bad practice. A pair of levers, as shown in Fig.
14, can be made by any one, and you may be sure that their use will not
be liable to jag a hole in the inner tube during the removal process.
When the inner tube is put into the outer casing, or tire, as it is
called, powdered talcum should be liberally applied, to the tube and
also placed within the casing. The tube is then put in and carefully
distributed and straightened out before the clinchers are put on.
A little air blown into the tube will prevent it from being pinched
under the flanges of the casing. The spare tubes should be inclosed in
a receptacle of some kind which will exclude light, and protect them
from heat. With the advent of the quick detachable rims of different
forms these troubles have happily disappeared in the modern automobile.
DAMAGES TO TIRES.--Many things must be provided for in the matter of
tire keep. The thing most necessary to guard against is _punctures_,
caused either by sharp stones, or nails. When a casing has a heavy
protective tread the inner tube may not be effected, but it frequently
happens that the outer casing is slitted for some distance, and
the great pressure forces the thin wall of the inner tube into the
slitted opening, and it is thus ruptured, not on account of its being
punctured, but because the outer tire did not afford protection against
the pressure.
REPAIRS TO TIRES.--It is not a difficult job to repair tires, and the
apparatus for doing it is very simple. Rubber, in its natural state, is
a white, thick, milky juice, which after several heating and refining
processes becomes dark and sticky.
VULCANIZING.--When in this condition and properly mixed with sulphur,
it may be vulcanized, which destroys the stickiness, and makes it firm
and elastic. Vulcanizing is a kind of baking process, the maximum heat
being about 275 degrees, but generally less. The time required is
from 12 to 15 minutes, dependent on the thickness of the mass to be
vulcanized.
[Illustration: Fig. 15. Vulcanizer.]
When the torn or cut portion of the tube or tire is carefully cleaned,
it is filled with the plastic rubber, and the heater is applied. The
heater, one form of which is shown in Fig. 15, is merely a shell with a
heater connection, and this being partly filled with water, generates
steam, the temperature of the shell being, of course, dependent on the
pressure of the steam developed.
To repair the inner tube, it should be first rubbed with sand paper,
and liquid rubber cement applied. When this becomes tacky apply the
patch and dry. It is then ready to be vulcanized.
OIL AS AN ENEMY OF TIRES.--All literature on the subject of tires give
warnings as to the insidious character of oil, which deteriorates the
rubber. Most manufacturers now make an oil proof quality, but the
cheaper grades are not to be depended on.
The action of oil shows itself in several ways, but principally because
it dissolves the rubber.
NON-SKIDDING TIRES.--Various means are provided in the shape of tire
treads to prevent skidding, the most important being vacuum cups,
the herring-bone formation, and various ribbed or ridged surfaces.
Nevertheless, for smooth asphalt pavements, chains or similar
substitutes are found most satisfactory.
Sudden application of the brakes, or the sliding of wheels on hillsides
or the skidding of the car in making short turns at too great speeds,
are the most destructive things for tires, however good they may be.
TIRES FOR CITY USE.--A tire which may be of good service for country
roads, might not be available for city work. The tendency of many
drivers is to hug the curb too closely, and the result is a wear on the
side, which is its weakest point. It is like the side of a shoe, the
upper of which can be readily worn through, whereas the sole will stand
hard usage.
In country use the great danger is in the winter months, where the
wheels must pass over or along frozen ruts. There the same difficulties
of side wear are liable to destroy the best material.
SIDE SLIPPING.--The same remarks apply to the weakness of tires due to
side slipping. The fibers of the fabric are ruptured at the weak point
and the least external abrasion assists in destroying it.
[Illustration: Fig. 16. Turning Action on Front Wheel.]
FAULTY ALINEMENT.--Another cause of ruptured tires is attributable to
improper alinement of wheels, due to the wheel being not exactly true,
through a bent axle, or improper adjustment. This is more frequently
the case with front than with rear wheels.
It will be readily understood that while the rear wheels have the
traction applied to them, the front wheels, fixed as they are, to the
short turning knuckles, are affected by a movement diagonally across
the tire, at every turn which is made.
This is shown by reference to Fig. 16. The movement of the car is in
the direction of the arrow A, consequently, when the wheels are turned,
the momentum of its forward end is in the direction of the arrows B B.
When the turn is to the right, the strain is on the inside of one tire
and on the outside of the other, and when the movement is to the left
the conditions are reversed in the stress, and this explains why the
tires of front wheels are so liable to yield, in all cases where turns
are made at high speeds.
BROKEN FABRIC.--The fabric of a tire may be ruptured without giving any
indications on its outer side. When there is a strong impact force,
like a transverse ridge, which will force in the tire, several things
occur. First, the body of the tire is flattened out so that it has a
bulging cheek on each side; and, second, a strain is produced on the
longitudinal fibers.
BRUISES.--The result of such a severe bruise is to cause a break,
not transversely, or longitudinally, but usually, obliquely, for the
following reason. The fabric has one set of its threads running across
the tire, and the other set around the perimeter. This arrangement of
the fabric usually prevents a straight break in either direction, and
the weakest part of the fabric is across the diagonal direction.
[Illustration: Fig. 17. Illustrating the Strain on Fabric. Fig. 18.]
Try the experiment with a handkerchief, as shown in Fig. 17 by
stretching it in the direction of the threads; and then look at Fig.
18, in which case the tension is diagonally, or across the corners.
This will be sufficient, probably, to suggest to your mind the reason
for the break on diagonal lines.
The rubber material is not sufficient to prevent the stretch which the
fabric permits, hence the break follows.
UNDER INFLATION.--To permit a wheel to run flat causes a tire to
stretch more on the tread than along the clinch line.
STRETCHED TIRES.--A good illustration of this is shown in Fig. 19,
where the tread is a succession of irregular wavy surfaces, whereas the
sides remain round and full.
Many attribute this to poor or defective tires. The best tire in
the market will show symptoms of this kind, if allowed to run when
deflated. In such cases the flatness produces a continual pouching out
of the sides, which follow the wheel around, and tend to produce a
creeping of the fabric.
[Illustration: Fig. 19. Effect of Flat-Tire.]
In time the rubber works away, or along on the fabric, until it becomes
stretched at the tread, and all the pressure in the tire will not again
restore it to the proper condition.
BLISTERED TIRES.--A blister is a plain case of the rubber being
separated from the fabric. At first the injury may be a small cut down
to the fabric, which, after being neglected for a time, permits sand to
enter, and a grinding takes place, each movement of the parts causing
a further separation, and pressure expands the rubber, until, finally,
it bulges out and gives an unsightly appearance, as well as starts the
tire on its road to destruction.
Such defects can be cured, if taken in time, as many compounds are on
the market for this purpose.
RIM CUTTING.--This is caused by sand or sharp particles being forced
in between the tire and edges of the rim, which causes a wearing out
at the contact points. Insufficient air is another cause. The tires
flatten and are then cut by the metal.
Frequently the tire is too small for the rim, and this is always bad
for it. Heavy loads will cause cutting, because the tire will be
flattened out, although inflated to the proper tension.
It is good practice to turn a tire, when one side wears more than the
other. This wearing on one edge excessively, shows some defect in the
wheel alinement, which needs correcting. Possibly the wheels may not be
parallel. This is a frequent trouble with front wheels, on account of
the bending of the arm which runs from the knuckle.
INFLATION PRESSURES.--Manufacturers of tires furnish data with respect
to the proper pressures for their products, and these vary somewhat,
and it is wise to observe the pressures which they indicate for the
different sizes.
EXPANSION OF HEATED AIR.--There is another cause of tire expansion,
not generally considered, which is due to the expansion of heated air.
It is not infrequently the case that a tire will, in running, heat
up fifty or sixty degrees, which means an expansion of one-eighth the
volume of air within the tube. If, therefore, there is any weakness in
the walls of the tire, a blowout follows.
As this heating is liable to take place to a greater extent in the
summer than in winter, it is obvious that it is better to under inflate
during that period, than to have an over pressure, particularly with
old, or considerably worn, or injured tires.