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Mercedes shown at Fig. 208. In the former, the wheel spindle is attached to a central body member of forged steel that fits in a yoke at the end of the axle and which rotates on a through bolt passing through the axle and wheel spindle boss and forming a bearing for these members as well as holding the assembly together. In the Mercedes type the wheel spindle is attached to a yoke member while the axle is provided with a simple bearing boss, the two parts being held together by a bolt as in the construction previously outlined.

Q. What is the “caster” axle construction and its advantages?

A. Forms of front axles having a peculiar steering spindle construction in which the wheel spindle center line is carried back of that of the axle proper are termed “caster axles” because the wheels tend to trail along and run straight even if the tie bar joining the two wheel spindles should break or become loose. It is contended that this form of axle provides greater safety on account of the wheels tending to travel in a straight path automatically. Other claims of easier steering and longer tire life are also advanced by adherents of this method of construction which is not very widely used.

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Fig. 208.-Front Hub Mounted on Mercedes Type Steering Spindle.

Q. What types of bearings are generally used in front wheels?

A. Front wheels are invariably mounted on anti-friction bearing of the ball or roller form. The wheel hubs outlined at Figs. 207 and 208 are carried on ball bearings while the wheel spindles of the heavy truck axle depicted at Fig. 202 and that of the touring car axle at Fig. 201 are mounted on taper roller bearings. A full discussion of anti-friction bearings and their advantages is given in Lesson 25.

Q. How are the springs secured to the front axle?

A The springs usually rest on pads or spring chairs, either attached to the axle as in the built-up tubular construction or forged integrally in one-piece axles and are kept from moving out of place by means of U shaped spring clips which straddle the springs and pass through the spring pads or chairs where they are held securely by means of locking nuts. The construction of a spring pad and arrangement of spring clips are clearly outlined at Fig. 202.

LESSON TWENTY-FOUR

WHEELS, RIMS AND TIRES

Q. What types of wheels are used for automobiles ?

A. Automobile wheels may be divided into two main classifications, those made of wood and the forms composed entirely of metal. Wooden wheels are generally of the artillery type, while metal wheels

may

be any one of four different forms. The most common metal wheel construction is the wire spoked form similar in appearance to those used on bicycles and motorcycles. Other forms are composed of two metal discs riveted to the hub at the center portion and together at the rim. There is another method of metal wheel construction patterned after the artillery wooden wheel excepting that it is made up of tubing and channel sections brazed together to form the complete assembly. A form of metal wheel that is receiving some application in heavy vehicle service is composed of a large steel casting, having fewer spokes than the usual, artillery wheels. These spokes are cast with flanges or ribs which act as a reinforcement and the wheel is a very substantial member.

Q. Describe construction of artillery wheel.

A. The wooden portions of an efficient form of artillery wheel used for pleasure cars are clearly shown at Fig. 209. The spokes, which are made of hickory, are joined together at the central part of the wheel by a series of interlocking mortise and tenon joints which form a very strong assembly and they are inserted into holes in a wooden felloe at their outer ends. The complete artillery wheel with metal hub and rim in place is shown at Fig. 210, while the two forms outlined at Fig. 211 show clearly the method of holding the lower end of the spoke securely between the main hub casting and the metal flange which acts as a clamping member. The main casting serves as a housing for the bearings on which the wheel revolves.

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Fig. 209.-Wooden Parts of Typi. Fig. 210.—Heavy Artillery Wheel cal Artillery Wheel

for Motor Trucks.

The wheel shown at A, Fig. 211, is a lighter form than that outlined at B and is intended for application on the front axle of a motor truck. The heavier and stronger wheel with sprocket and brake drum attached is one of the traction members that revolve on the rear axle. The rubber tires with which these wheels are provided are not shown in this view but the appearance of a complete wheel with sectional block tires and retaining flanges in place is clearly depicted at Fig. 210.

Q. Describe a typical cast-steel wheel for motor trucks.

A. Heavy cast-steel wheels intended for use on a large motor truck of German design are shown at Fig. 210-a. That at A is a front wheel and is fitted with a single tire. That at B is a rear wheel with rim of sufficient width to take two solid rubber tires side by side. The wheel construction consists of a steel casting having cored spokes and rim to give it lightness, provided with a plain bearing hub. The construction of the front and rear wheels is similar except that the hollow rim and spokes of the latter are of larger size and the spokes are provided with bosses through which the bolts holding the driving sprocket and brake drum in place are secured. The use of plain bearings is not general on American motor trucks on account of the friction present when the wheels are heavily loaded. Plain bearings are suitable only where truck speeds are very low and the motor has a margin of power over the actual requirements.

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Fig. 210A.-Motor Truck Wheels of German Design Made by Steel

Casting Process.

Q. Outline construction of wire spoke wheels and state their advantages.

A. A tangent spoke wire wheel adapted for automobile use complete with tire is shown at Fig. 212, while the various methods of wire wheel construction in vogue are outlined at Figs. 213, 214, and 215. Wire wheels may be of either the double or triple spoke construction as indicated at A, Fig. 213. The double spoke type follows lines that have been established as standard in bicycle and motorcycle construction and differs but slightly from the wheels used on the lighter vehicles except in the matter of structural strength of the components. The triple spoke construction has been devel

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