Like all other constructions the above type offers certain disadvantages. The overall length of the vehicle must be greater in order to permit the location of the motor under a removable hood. In many cases this added length does not operate as a decided disadvantage for average application in which the machine must be maneuvered, in narrow thoroughfares, backed up to curbings and garaged in valuable space, every inch of added length makes itself felt in the owner's purse. With the question of load distribution it may be said that careless freight handlers are just as likely to place the light, bulky portion of a miscellaneous load forward of the axle, and to burden the overhang with heavy material, occupying little space, as they are to reverse the loading. Concentration of both driving and load stresses to a maximum degree upon one pair of tires causes loss as far as tire economy is concerned.
Turning now to the type of construction representative of the second class of design, we find illustrated in Fig. 2, a vehicle in which the driver's seat and controlling elements are superimposed upon the motor space, the load being apportioned fore and aft the rear axle in an approximate ratio of 2 to 1. The result of this load distribution is that it does not permit of a traction ratio so high as does the previously described type, and steering is perhaps less sensitive. But when the high friction coefficient of rubber is considered upon average road surface and the fact that roller bearing steering heads are to be found in most commercial car axles of modern design, then these two conditions become relatively important. In respect to the load distribution, the latter construction possesses advantages over the first type. For a given loading space the construction in Fig. 2 permits of marked compactness in overall length, with the attendant advantage of ease of handling, minimum projection into through fares when backed up to a curve and economy of garage space.
These relative advantages are gained at the expense of motor accessibility. Doors or removable panels are usually fitted to allow access to the motor from the side, while floor boards permit limited access from the top. When front fenders are provided the access from the sides is also materially reduced. This notable lack of accessibility arises, first, from the necessity for rigid and fairly bulky superstructure for carrying the driver's seat and second, from the fact that a maze of control levers, brackets and rods are frequently located in the space which should be reserved for access to the motor and its accessories. Many trucks show a marked improvement in this construction, however, at best it leaves much to be desired in the way of accessibility.
There is still another type, Fig. 3, which has been introduced several years ago, in which an attempt is made to combine the advantages of the first and second types is apparent. This has been accomplished in a measure, by mounting the motor in a more or less accessible position between the two seats. A removable hood is generally fitted, but the net result is almost invariably inferior from a standpoint of accessibility to the construction shown in Fig. 1, although from the same viewpoint it is an improvement over Fig. 2. The advantage of longitudinal compactness is retained, moreover the weight is well distributed between the front and rear axles.
In making the illustrations, the writer has taken pains to have the wheel base (i.e., center of front wheel to center of rear wheel), and the length of the loading in equal proportions in all illustrations so that a good idea can be obtained as to relative overall length and weight distribution.
It can readily be seen that in the point of overall length, the construction which embodies placing the driver's seat over the motor has the advantage of requiring less length than the other two types. While, on the other hand, the question may be asked, are the advantages to be gained by placing the driver's seat over the motor great enough to outweigh those claimed for other constructions?
The general advantage of either construction presents itself when the conditions of operations are considered. The vehicle may be operated in districts when traffic is congested, which would favor class two, while on the other hand accessibility may be the chief point to be considered, which then would favor class one. While certain conditions may suggest the selection of class three. In the smaller vehicles class one is greatly desired owing to its pleasing appearance when fitted with expense bodies.
From the above it can readily be understood that the construction of a vehicle is somewhat depended upon the conditions of operation and nature of the work it has to accomplish.