• Does PARTIAL LOADING Save FUEL EXPENSES?
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QUITE often I. am asked what is the effect upon fuel consumption of running light: suppose a vehicle is running empty one way. what difference does. that make to the figures for fuel cost? Linked up with that is the further question: how should the figures for consumption quoted in The Commercial Motor Tables of Operating costs" be amended to suit varied conditions of loading?
The answer to the latter question is that the figures in the Tables give averages for all kinds of loading. If a vehicle is running fully loaded all the time, the cost per mile for fuel may be expected to be higher than average. If the vehicle is running only part-loaded for most of the time, the cost of fuel per mile may be expected to be somewhat less than the amounts quoted.
The figures given in Table 1 indicate, .roughly, what may be expected according to the various conditions specified. They are not pht forward as being precisely what may he expected: they are approximate only, as is bound to be the case, as other factors enter into the calculations, factors too numerous to be accounted for in any practical way.
Margin of Error
Eveit taking fuel consumption and costs alone, as I am doing in this article, there is such a margin of error that I sin putting the figures forward diffidently, with a plea for lenience in any criticisms which may arise.
I would far rather deal with the matter on the basis of the average figures given in the Tables, leaving the inquirer to make up his own figures by actually testing his vehicles directly, so that he will have no need even of averages. Those who do that should use the Tables in two ways: (a) for purposes of comparison with their own figures, and (b) in connection with work in prospect involving the use of types and sizes of vehicle of the use of which the operator concerned has not had any experience.
The predominant item in running costs is usually the expenditure on fuel, be it petrol or oil. It is, fortunately, the one concerning which most users have some information and it is, therefore, eaSy to point the argument that 1 have just put forward by taking fuel consumption as an example.
Experienced users and readers of these articles will hardly need to be told how liable fuel, consumption is to vary, how it is different with the same types of vehicle engaged upon the same kind of work. They know at !east enough a26
to he receptive to any suggestion that it varies in other ways.
A few words about the conditions which most affect fuel consumption may be useful here. There are circumstances due to the 'particular kind of work upon which the vehicle is engaged; there are those connected with the type of country which the vehicle has to traverse, and there are those brought about by its use at the hands of drivers and those whose business it is to maintain it.
I have often cited building construction as an activity which is hard on a vehicle engaged in carrying the necessary materials. These materials are often difficult to handle and, therefore, difficult to load in such a way as to give the vehicle what might be termed "a chance." Often enough new buildings are erected in advance of the construction of the roads which will eventually lead to them. That means that the vehicle, in the course of each journey, has to traverse unmade ground, and even if there is a road in existence. the actual delivery of the materials often involves leaving that road, with correspondingly rough treatment of chassis and tyres and inevitably increased consumption of fuel brought about by prolonged manceuvring in low gear.
View Confirmed
These views of mine on the conditions attaching to,the conveyance of building materials and the way in which it is hard on the vehicles engaged upon it were confirmed the other day in the course of a conversation with a builder. He told me that the life of a popular make of light lorry is, according to his experience, under two years.
As the annual mileage on this class of Work is invariably moderate, my friend's experience points to the fact that depreciation is at thh rate of a 50,000-mile life instead of the average of 150,000, thus increasing the single item of depreciation by as much as 200 per cent. All the ether items of running cost are similarly affected, although not to the same extent.
It will readily be agreed that there are at least a dozbn trades that, by reason of the conditions under which their transport is carried on, would be likely to affect-to a greater or lesser extent, the running costs of the vehicles employed in them.
It is not only the circumstances involved in the kind of work itself that affect costs adversely or otherwise, but also the way in which the vehicle is driven, hOw it is maintained, and the attention it receives at the hands of those who are responsible for its upkeep. Fuel consumption, tyre life, wear of brake facings and the general condition of the transmission can be aggravated by 100 per cent, if conditions are unfavourable.
Now, if we take extreme cases, say on the one hand a particular type, size and make of vehicle employed on work which is favourable to good performance, in the charge of a good driver and carefully maintained, and, on the other. one which is at work under difficult conditions, in the hands of a careless driver and is neglected, then it will be realized that an extremely wide variation in the running costs is likely to result.
I am stressing this point just now because I am about to depart from a rule to which I have most 'strictly held for many years, 'namely, never to discuss differences in fuel costs involved in light and loaded running. The reason for the rule is a good one, and it still exists. It is not right to hold out hopes of economy in fuel consumption as a means for cutting haulage rates when other conditions may affect tllat item in another direction so as not merely to eliminate the anticipated economy but to cause increased rather than diniinished expenditure.
Offset Any Economy As a-simple example of a condition of use which might easily upset any such calculation, I, need only compare the fuel consumption of a vehicle constantly engaged in congested traffic with another almost continually working upon long non-stop runs along main highways. The consumption of fuel in the former case' may quite easily be 30 per cent. higher than in the latter and that increase will. as the figures which I am about to disclose demonstrate, inure than offset any economy which is the outcome of light running.
I do. however, receive many inquiries from hauliers in which the condition of light running is mentioned as an indication that the inquirer anticipates that some measure of economy may possibly be effected as the outcome of that condition. I have endeavoured. to find a figure for consumption which will meet these circumstances. At the same time. I should warn allthose to whom these figures have an appeal that a careless driver, or some traffic condition such as one involving the negotiation of several miles of road where one-way traffic persists, will upset all these calculations and render the resulting figures valueless.
I do not propose, in this discussion, to go through the
whole range of sizes and types of vehicle, but shall take only the most popular oil-engined machines. I shall also confine my attention to goods vehicles, because the conditions of passenger transport are rarely such as to make it possible to state with any degree of accuracy what proportion of load is likely to be carried on any particular journey.
The only exception to this is where a coach is used for carrying workmen only one way, taking them to their work in 'the morning and bringing them back home in the evening. Readers who engage in that class of work can, by reference to a corresponding size of goods vehicle, obtain some idea of the proportionate savings.
I would like to emphasize once again that these figures must be used with only the maximum of reserve, but, given that qualification, my readers may find the information useful in cases where quotations are called
This Guy Otter is one of several vehicles Of this make operated in South Africa by the Natal Milling and Trading Co. for the transport of groceries and milling products in the Durban area. The wheelbase is 1.4 ft. 9 in. and the engine is a Perkins P6 unit. The .all-steel body is 18 ft. tong
and has a tarpaulin rail.
for in connection with long-period contracts, the detail conditions of which they are acquainted with to a sufficient extent to enable them to judge how far these figures may be applied with safety.
The accompanying table gives figures which would apply
• in the case of vehicles Which invariably carry a full load; and there are those concerning machines which, on the average, carry burdens that are such that the vehicle is loaded for the equivalent of 75 per cent. of its time. The third series is, perhaps, the most interesting as it givesfigures for a vehicle which is fully loaded in one direction and invariably returns empty. Finally, there are given consumption rates and costs of fuel per mile for machines running light. In calculating the cost, oil fuel is assumed to cost 4s. per gallon. It will be noted that it is not only in connection with the larger vehicle that the difference in consumption is worthy of note, as the•following calculation will show.
Take as the first example, a 3 ton van, and assume it is running 500 miles per week. The expenditure on fuel when it is fully loaded all the time will amount to £5; whereas if it is loaded only halt the time the fuel consumption will invOlve an expenditure of only £3 17s. Id. for the week, a difference of £1 2s. lid, per week.
In the case of a 7-tonner covering the same weekly mileage, the expenditure under fully loaded condition's will approximate to £8 6s. 8d. and if loaded only 50 per cent. £.6 13s. 4d., a difference of 13s. 4d. per week.
The weekly mileage is, of course, an important factor. If, for example, the 7-tonner covers 1,000 miles per week, as is not a rare experience, the cost of fuel, according to the first set of conditions, fully loaded for 100 per cent, of the time, will be £16 13s. 44. per week, whereas if the loading is only 50 per cent., the expenditure on fuel will amount to £13 6s. Ed., a difference of £3 6s. 8d. S.T.R.