What is CAPACITY ?
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Asks P. A. C. Brockington, A.M.I.Mech.E.
UNLESS the body sides and rear door panels of a vehicle are flat or have a true geometrical shape, it is virtually impossible to calculate the precise load capacity. In a large van, small irregularities in the panels are of little practical importance in the determination of useful space, but in vans of less than 10 cwt. they may be serious.
How .accurate are the capacity figures fisted by manufacturers of such vehicles, and if the total given is a true evaluation theoretically, does it represent useful space to the average operator? • In some instances, the specifications do not state whether the space available beside the driver is included. Such an omission can be deceptive. Moreover, according to reliable reports, some makers take the maximum width for the basis of calculation and some the mean width.
Leaving in abeyance consideration of those features which restrict loading by virture of their position rather than size, the prospective user would be reassured to know that the capacity given was theoretically correct, Possibly the only satisfactory method of evaluation would be by filling the van with liquid or pellets after partitioning and sealing the driver's compartment (and the passenger space if this were not included in the specification) and measuring the capacity by pouring the contents into a graduated receptacle.. This would obviously present difficulties if the medium used were a liquid, but s10 the alternative method would be comparatively straightforward, particularly if the pellets were specially designed for the purpose.
The cost involved would be relatively negligible to the makers of vans produced in quantity and based on popular private-car chassis, which form the majority in the class under 10 cwt.
The styling appeal of vehicles of this type, as distinct from an acceptable appearance, is more important than the styling of large vehicles, because the operators often use them for pleasure as well as business. The opinions of the family sometimes influence the choice.
Some sacrifice of utility to styling is inevitable, otherwise the body would be rectangular, and its shape would be incongruous in comparison with that of the modern bonnet, front wings and other standard chassis components.
Shaped sides that slope inwards and off-vertical doors and rear panelling reduce the accommodation that can be used for large objects, and frequently loading difficulties are unnecessarily increased by such features as inward curves at the top corners of door frames and the use of gusset plates at these points. The wheel-arch can be regarded as an unavoidable encumbrance, but careful design can save valuable space. The distance between the arches is of first importance to operators carrying large, rectangular objects, and the floor area behind the arches is another factor that may affect the usefulness of the vehicle.
A valuable specification would be the dimensions of the largest box that could be carried in the vehicle and, of course, loaded through the doors. Straight-sided wheel-arches have obvious load-carrying advantages for some goods, which could offset a loss of capacity occasioned by their use.
The position of the spare wheel is another factor which, may, or may not, be taken into account" when the capacity is estimated. If it is located in the carrying space, it may obstruct. the load to an extent which is out of proportion to its size. When it can be easily removed to a position beside the driver, it may in practice be less wasteful of space, but projecting brackets can still be a hindrance.
Housing the wheel under the floor gives a neat appearance and increases the effective floor space, but the higher loading level may be ,a disadvantage, and raising the roof to provide the necessary total capacity may necessitate dome alterations which are not acceptable on the grounds of appearance. A high floor level may also be criticized if the passenger space is employed for load carrying.
Other detail features which may be obstructive include fuel-filler pipes, electrical connections and door-catch arms. Wiring plugs are easily damaged and this may lead to rear-light failure, and the projection of a sliding member into the interior when the door is closed may not be noticed until it has punctured a frail carton or has been bent by contact with a solid article.
A close-fitting frame saves space, and it should preferably be free from sharp edges. The back rest of a seat that slopes over the van floor also reduces the useful payload capacity of the body.
The area of the rear door opening above the floor, compared with cross-sectional area of the body, indicates the bulk-loading potential, and some operators regard loading height as such an important factor that they advise a check of the floor level with the vehicle laden and unladen before a purchase is made.
The production of a standard formula for measuring the capacity of vehicles might well be undertaken by the Society of Motor Manufacturers and Traders in the interests both of makers and operators. The present lack of uniformity is certainly causing dissatisfaction and the discrepancies in the claims of various manufacturers are misleading to users. the (Above) A spare wheel mounted inside the vehicle reduces the floor area, but may be preferable to housing the wheel under a raised floor. Frame members that stand out from the body panels could cause obstruction when the van is fully laden with bulky packages. A flat-topped wheel-arch can be valuable as a shelf (Left) Electrical connections that project into the body are easily accessible, but occupy space and are liable to be damaged. Packages slipping off the rounded wheel-arch could come into direct contact with the terminals. (Right) In building a flat floor, valuable loading height may be lost. The intrusion of the door pillar may steady the load, but may also be inconvenient in unloading from the front.