USEFUL LOAD CAPACITY.
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Some Considerations Bearing Upon the Selection of the Most Suitable Size of Commercial Motor Vehicle, and Showing the Relations Which Exist Between the Useful Load-carrying Capacity and the Cost Per Mile and Per Ton-mile.
FOR THE PURPOSE of establishing general principles rather than exactly estimating the cost of operating some particular vehicle, it will serve our purpose to take, as a basis of calculation, figures which are admittedly better than those which can at the moment be obtained in the:majoritk of instances. If we assume fuel to be fairly cheap, labour available at reasonable cost, and roads to be of good quality, a. van capable of carrying one ton to 25 cwt. may be operated over an annual mileage of about 22,500 at a cost of about 5d. a mile. The figure taken corresponds to 450 miles per week, assuming 50 working weeks in the. year, or to 75 miles a day, taking_ six working days in the week. Of course, it is not always possible to find useful work for a van over so big a mileage but this applies with equal force to the coraparative figures for other types which will be given below.
Assuming our one-tonner to carry its full load over its full mileage, the cost per .ton-mile is evidently the same as the cost per mile, namely, 5d. . Next take a typical two-tonner working under similar conditions. Its speed will be somewhat slower, so we may say that it is capable of covering 18,000 miles hi the year, or 60 miles a day. The cost of operation may be about qd. a mile. With a full load this means 31d. per tonmile.
With a three-tonner we may put the annual mileage at 15,000, or the daily mileage at 50, and the cost per mile at about 8d. the cost per tonmile being one-third of that amount.
For a five-to:aner we must again reduce the mileage somewhat. We may put it at 13,500 for the year, or 45 miles per day, and we may estimate the working costs at 10-id, per mile, the cost per ton-mile being one-fifth of that.
As already stated, these figures are all on the favourable side : they are not impossible, but they are at the present improbable, of attainment ; they are, however, all about equally favourable, so that they may be regarded as fair if used merely for lourposes of comparison of the various tynes of vehicle named. • In selecting a, vehicle, we may consider first the question of mileage. If we want to cover much more than 45 miles in a day in a single run out and home, the five-tonner will be to big for us. If, on the other hand the total daily mileage to be covered is about 75—made up of a number of fairly .short runs—and the load to be earriei daily over that distance is five tons, we could do the work by using a couple of five-tonners, or alternatively, by employing five onetanners. The choice depends partly on whether our load is of such a character that it can be conveniently Fig. 2 shows the practical weekly Son-mileage of vehicles of various load-capacity, assuming full mileago and full load throughout. The term "ton-mile" means here the net ton mile—that is to say, it is Wised on the weight of the useful load and does not take into account the weight of the vehicle itself. It is evident that if either the load or the mileage be reduced, the practical weekly ton-mileage will be reduced in the same proportion.
We may turn now to Fig. 3, which shows the comparative costs per ton mile for vehicles of, various load capa cities. This curve is obtained by using the figures given above. It as sumes full load and full mileage in every case. If the load actually carried on the vehicle were reduced, the cost per ton-mile would increase in the same proportion. If, however, the mileage were reduced, the effect would be different. This, as explained in a previous article is due to the fact that some of the cats of operation re sult directly from the use of the ve hicle and the mileage covered by it, while others are standing charges which have to be met equally whether the mileage is great or sinall. The point to note about Fig. 3 is that the greater the capacity of the vehicle the lower the cost of carrying a ton over the distance of a mile, always assuming that the big vehicle can be kept as fully loaded as the
small one.If the load be a constant factor, then, as shown in Fig. 4, it is evidently best to use the smallest vehicle capable of carrying that load.
Fig. 5 shows the comparative costs per ton-mile for various types of vehicle, carrying in each case various loads, but assuming the full practical mileage in every instance. It is, of course, in practice almost impossible to provide a full load at all times for a vehicle. Fig. 5 shows, for example, that if the cost per ton-mile with the five-toriner fully loaded is 2.1d., this cost will rise to about 2.7d. per ton-mile if the average load is only four tons ; to about 3.5t1. per tonmile if the average load is three tons and so on. . The curves taken together illustrate a point already made. Thus, a, three-tonner fully loaded costs about 2.7d. per ton-mile, If our loads will never exceed three tons, it is therefore cheaper to use a threetonner than a five-tonner. If, however, we can find
loads of not less than 31 tons, then from that point
upwards the five-tonner, though not quite fully loaded, will show a lower cost per ton-mile than the three tonner fully loaded. Similarly, a three-tonner carry
ing a load of 2i tons will be just as economical in cost per ton-mile as a two-tonner fully loaded ; and a
five-tonner carrying just over two tons as an average load will be as economical in cost per ton-mile as a one-tanner fully loaded. These comparisons can be readily drawn by noting where the horizontal lines
(Aas Bb and-to) cut the various sections. If we draw any horizontal line, such as Ee, it will help our com
parisons. This line shows that, from the point of view of cost per ton-mile, a five-tonner carrying
tons is the equal of a three-tonner carrying about 2'3 cwt., a two-tonner carrying about 18 cwt., or a onetonner carrying about 15 cwt. average load.
In practice we cannot provide exactly the same load on every occasion: we have, therefore, to take into acceunt the fact that on some occasions the load may be unusually heavy. If, therefore, we buy a vehicle only capable of carrying our average load, we are ,without any reserve against such an emergency. Generally speaking, an exceptionally heavy load, if it is only of occasional occurrence, can be dealt with by
calling upon the vehicle, which is usually adequate,, to cover once in a way an exceptionally heavy mile044
age. If the occurrence of very big loads is comparatively frequent, this course cannot be adopted, and a vehicle o4 larger load-capacity must be selected in the first instance.
We must also remember that in many classes of business the mere fact that a motor begins to be used itself increases the amount of work that becomes available for that motor to do. For example, the retail trader, by adopting motorvans greatly increases his area of delivery by load. If, then, in selecting his vans, he bases all his calculations on the mileage or ton-mileage of his old horsed-vehicles, he will presently find that his motors are either not big enough or not numerous enough for his work. The various figures in this article show clearly enough that, wherever it is practical to use them, a comparatively few large vehicles are cheaper to operate than a proportionately greater number of smaller vehicles of equal aggregate capacity. Despite this fact, the light van may often be preferred, not on the grounds of economy per ton-mile, but because the distribution of the points at which deliveries have to be made is such that a few big vehicles could not cover the ground sufficiently often. The superior speed of the smaller models is also important in some businesses in-which great promptitude is an asset. Altogether, the writer does not suggest that the study of the diagrams given in this article will inevitably lead to a correct decision. He maintains, however, that such a study will give the prospective motor user cause to think carefully about a number of points which ought to be taken into account in his selection of machines, and will therefore help him in that selection by making it less likely that he will omit to consider, some factor which is in reality of considerable, if not actually of vital, importance.
Up to the present it has not been our habit to regard the Japanese as likely competitors in any sphere of motor manufacture; but, backed by the experience of Mr. A. C. Hills in his recent tour through the East, it now seems fairly safe to prophesy that the British firms which manufacture the smaller and cheaper classes of accessory: are likely to find-Japanese competition quite a serious matter when the war is over. The Japs are magnificent copyists, and are able to get really skilled labour at a very low cost. There appears to be nothing to prevent them from turning out lamps, horns, and so on of reasonably good quality and at an extremely low price. subdivided, but it depends more often on which is the cheaper method of haulage.
Fig. ). shows by means of a curve the approximate weekly mileage that can be covered by vehicles of various load capacities. The lighter classes of vehicle Cal). travel more rapidly than the heavier without undue 4 vibration, likely to lead to wear and tear. Moreover, the law allows them somewhat higher epeeds. More often than not, however, we have to consider' not merely the mileage but the load that can be carried over that mileage. For purposes of comparison we then use the ton-mile as our unit.