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.
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.