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.
CHAPTER IV
THE STEERING GEAR AND BRAKES
The Steering Column.—This is a very important mechanical element of the car. Its direct useful functions are to carry or hold the mechanism for steering the machine, and for the motor control, controlling the air supply for the fuel, as well as for regulating the sparking mechanism.