THE principal functions of a tire on an automotive vehicle are: (a) to carry the weight of the vehicle, to cushion it over road irregularities, and to eliminate noise; (b) to provide sufficient traction for accelerating, driving, and braking; and (c) to provide adequate steering control at high speeds.
Adequate steering control, taken for granted in the early days of automobiles, becomes highly important as driving speeds increase. The property of tires whereby steering is accomplished is called cornering power. This power is practically negligible in hard wheels, but is possessed by pneumatic tires due to the extended area of road contact.
Cornering thrust is developed when the plane of the rotating tire makes an angle with its path of travel. The thrust is proportional to this angle up to the point where slippage begins. When a tire is cambered, the cornering force is increased or diminished depending on whether the tire leans “into” or “away from” the curve.
Increase of inflation pressure or of rim width increases the cornering power. Certain structural features of the tire itself affect its cornering effectiveness. However, any change, whether internal or external, which improves cornering power, makes the cushioning ability of the tire worse.
Tread wear continues to be the most important aspect of tire performance. Of the 1934 cars, with various types of springing and of load distribution, some cause much faster tread wear than others. There is also a tendency, as compared with previous years, for rate of wear of front tires to approach that of rears.