THE AXLE.--Axles are of two kinds, generally designated as “live,” when they turn the wheels; and “dead” when they do not turn the wheels, but simply support the weight of the frame and of the body. Dead axles are used with double chain drive, as, in that case, the sprocket wheels are attached directly to the sides of the wheels and the wheels turn on the studs, or ends of the dead axle. LIVE AXLES.--1. _Plain live axles_ originally consisted of a shaft without differential gearing, having one wheel fast on it, the other turning. Modern construction shows two axle shafts in a housing, the weight of the car, and the tooth pressure of the differential being carried by the axle shafts. 2. _Semi-floating axles_ have the weight of the car carried by the axle shafts, whereas the tooth pressure of the differential is supported by the housing, and only the turning effect or torsion is transmitted by the axle shafts. [Illustration: Fig. 7. Floating Axle.] [Illustration: Fig. 8. Semi-floating Axle.] 3. _Full floating axles_ carry the full weight of the car, and the differential bevel gear teeth pressure with the housing, so that the axle shafts carry no load but only the torsional stress. Both full and semi-floating constructions are applied to rear axles only. The front wheels are now universally applied to knuckles, which swing on vertical pivot pins at the ends of the dead axles. WHEELS.--Wheels are now in a transition state. The ultimate wheel has not yet appeared; but whatever its form or construction, certain things are essential. FLEXIBILITY.--In the ordinary wagon or carriage wheel, there is but little, if any, flexibility; but in automobiles, where speed is a consideration, elasticity, either in the rim, or in some other part of the wheel, is necessary. One of the reasons for this is, that on account of tire expense, motor wheels are smaller than carriage wheels. Making them smaller, however, produces certain disadvantages. One is that in going over the inequalities of the road, the axle on the small wheel has a greater vertical movement than on a large wheel, and the jar on striking an obstruction is more pronounced, also. These disadvantages, however, are more than counterbalanced by the elasticity of the invention. LARGE VS. SMALL WHEELS.--Fig. 9 shows a large wheel A, passing over a depression B. The large arc of the wheel does not permit the rim to go to the bottom. On the other hand, the small wheel C goes to the bottom of the depression, and the vertical distance which the axle of this wheel must travel, is three times as far as in the case of the wheel A. In Fig. 10, where the large wheel strikes an obstruction D, the angle of its upward movement, as designated by the line E, is much less than the impact force of the small wheel, as shown by the greater slope or incline of the line F. [Illustration: Fig. 9. Crossing Depression.] [Illustration: Fig. 10. Striking Obstruction.]