Road shocks must first be taken by the road wheels, through tire contact, and thence distributed, spreading out in all directions from the hubs if the wheels.
The artillery type of wheel consists of a set of spokes turned from very tough wood, generally second growth hickory, which arc clamped at their inner end be-tween flanges on a metal hub and at their outer end tenoned into a wooden felloe, which is surrounded by a steel band or ring. The spokes may he either of elliptic, square or rectangular section, and great care is taken to get the fiber to run exactly in the direction of the spoke length. It is common practice to split the spoke billets instead of sawing them.
The wood used in the spokes and felloes is made from wellseasoned timber, so that strength and toughness in the highest degree can be obtained. Second growth stock and stock From the lower portion of small trees yields the best parts.
In truck work when solid tires are used the spokes are of square or rectangular section, since these are stronger in proportion to weight than the elliptic spoke.
The greatest amount of trouble with the artillery wheel has been experienced with those used on very heavy trucks. The spokes ate eery thick and a comparatively slight shrinkage of the spoke causes them to loosen in their hub and the severe jarring, due to the use of solid tires, then has a very destructive action In order to deviate this difficulty and strengthen the spokes assembly at the center the Schwartz Wheel Co. make the miter of the spokes interlocking, while other makers provide keys between the miters or adjacent spokes.
Cast-stell wheels are now gradually coming into use, while pressed steel wheels are also used on some of the vehicles having less than two tons capacity. The steel wheel is very popular in foreign countries, and American manufacturers are gradually using them. In some cases they have not succeeded, while in others they have given excellent service, which is also true of the wood wheel.
The advantages possessed by the steel wheel for heavy duty are strength, true shape, rigidity, concentricity of the hub and accurate design for the support of the load. In point of strength and elastic limit, the steel wheel well made, is superior to the wood wheel, and will sustain more in impact and side thrust. Another advantage is that they may be accurately machined and once round, they will stay so regardless of humidity, heat, etc., that affect most wood wheels. In design these wheels may have the brake drum, hub and flange cast integral so that there are no bolts and rivets to loosen or break. Considering weight, for vehicles of three-ton capacity and over, the steel wheel is lighter than a wood wheel of equal strength, while for two-ton vehicles both types are about equal in weight.
The pressed steel type of wheel for trucks up to two-tons capacity is somewhat lighter in weight than a wooden wheel of corresponding capacity. This type of wheel can l>e produced for practically the same price as wood wheels, when the complete wheel is considered.
The steel wheels vary in construction, and opinions differ as to which construction gives the best service.
An idea of the construction of wood and steel wheels can be obtained from the illustrations presented herewith and the descriptions which follow:
Fig. 259 illustrates the Nateo one-ton front wheel with demountable tire. The wheel has twelve square spokes which an turned into the felloe and retained in the huh by twelve bolts placed between adjacent spokes. The general form of the hubs is largely determined by the dimensions of the bearings and their necessary distance apart. One hub flange is generally made integral with the huh casting, while the other is free to be slipped over a machined cylindrical surface so as to be accurately guided.
Fig. 260 depicts the construction of the Mogul six-ton rear wheel which is equipped with 40 x 7 in. S.A.E. tires. There we eight spokes of rectangular section and eight spokes of square section. These are all of the same thickness, but the rectangular, ones are used for attaching the brake drum, and practically the same strength as the square spokes, as considerable stock is removed by the bolt holes. The hub holts pass through the joints of adjacent spokes as shown. The felloe is made to SA.E, dimensions, and the S.A.E. felloe band is shrunk over it.
Cast steel wheels may be either of the spoke or disc type, and both seem to be giving good results. The disc type either have a single or a double disc, depending upon the capacity. while the spoke type may have either tubular or cross-section.
The single-disc type is at present being used on the Nash Quad Trucks, and this application is clearly shown in Fig. 261. The essential features of this type of wheel are a cast hollow box section rim supported by a curved spring-like section to struts connecting with the hub. The disc includes a solid cast brake drum and container for the driving mechanism. The working parts of the drive are thoroughly protected from injury by the wheel disc and brake drum. It will be noted that the hub is cast integral and that there aRE no bolts and nuts to loosen except those which retain the internal gear.
Fig. 259. Natto Front Wheel.