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.