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OPINIONS and QUERIES

6th December 1946
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Page 43, 6th December 1946 — OPINIONS and QUERIES
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Which of the following most accurately describes the problem?

ROADS AND THEIR CONTROL

A T present I am employed as a taxicab driver, but, r-k previously, was travelling in all directions, mostly on light transport work. In 1925 I was driving in London for a firm of contractors and was with them during the general strike, when I used an ex-W.D. Peerless on milk transport. I believe that driving in London with its fairly wide roads is actually easier than in the confined areas of this town. There is, incidentally, a rubbercovered road here, which I hold is a danger

• I am sure the greatest crime against road transport was the raiding of the Road Fund.

During the black-out, the " islands " here were going down like nine-pins. I had an interview with the surveyor and suggested removing the red lights on them and employing lanterns with distinct crosses. This was carried out, and almost cured the trouble. I offered to drive this official around and show him other causes of .accidents, but all I received was a curt letter of thanks.

It seems that until the roads are controlled by 100-percent. road-minded men of an age which will enable them fully to understand the problems, we shall get nowhere., I believe in a strong mobile police force with men of the right type; the ordinary policeman is merely a pedestrian and knows little about motors.

I look upon the motor industry as the greatest business that has ever been developed, and wish to do every

thing possible to support it. S. C. FIELD. Oxford.

TYRE VARIATIONS AFFECT SOME MULTI-WHEELERS

AS an engineer I support "The Commercial Motor" with regard to the leading article, "Why Do Tyre Overall Diameters Vary?" (October 18).

. I feel that it ought to be pointed out to your correspondent Mr. W. L. Barnes, who, in his letter to you, published on November 1, endeavoured to make light of tyre-diameter variations, that there are on the Toads such vehicles as multi-wheelers with both the rear axles driven.

It is in connection with this type of vehicle that axle overheating takes place when excessive tyre variation is present. Perhaps I ought to point out that the reference to axle overheating is in connection with the worm drive.

In my opinion, an engineer who blamed tyre variation on a single driving axle for axle overheating is not worthy of his name.

At times when a fully matched set of tyres is not available and there is any tendency to overheating, it is possible to overcome this difficulty by making up the near-side set to approximately the same diameter, and the off-side set to a different diameter; the variation in this case is equalized by the axle differentials. Should a vehicle of this type be away from its home base and sufficient tyres not be available for matching up, I find it expedient to instruct the driver to disconnect the drive to the second rear axle by removing the intermediate propeller shaft; this relieves the " chasing " effect which creates the overheating.

Another point that your correspondent has overlooked is the " mating ' of twin tyres, one to another. In this respect, the smaller tyre of the two very soon shows signs of " seuffing " or uneven wear.

If this variation of tyre size be o. no consequence, perhaps he will explain why, to mention one manufacturer, Thornycroft has fitted a third differential. I

quote an extract from the latest brochure covering its eight-wheeler:—" A third differential is fitted in the foremost bogie axle, ensuring equal driving results from each wheel, and allowing each wheel to rotate at a speed best suited to its diameter, thus eliminating undue tyre wear" The remarks of your correspondent are interesting, but do not explain the editorial query, "Why do Tyre Overall Diameters Vary?"

Perhaps some authority, or the Tyre Manufacturers' Conference, Will reply to the "leader," which is backed by the Institute of Road Transport Engineers' With regard to the last paragraph in the letter from Mr. W. L. Barnes, all transport engineers in charge of fleets will confirm that the understanding of tyres and their application to vehicles is only one part of their very important and responsible job of "keeping the wheels

turning." JOHN HUTCHINSON, M.I.R T E Stockton-on-Tees.

[Since this letter was received, the S.M.M.T. has replied, on behalf of its Tyre and Wheel Technical Committee, to the queries raised by the Institute. A reference to the answer was given on page 338 of our issue dated November 8.—Eo.1 THE EFFECTS OF FITTING LARGER TYRES I AM running a 1946 Bedford long-wheelbase 5-tonner I and, in consequence of tyre shortage, am considering fitting the 36-in by 8-in, size on the rear wheels. Will you please let me know what effect this will have on the gear ratios, general running, etc., also what would be the error in respect of the speedometer

I may add that conversions with standard wheels have worked well on tipping wagons with lower ratios.

Bristol. C.B

[The maker of this vehicle does not recommend the fitting of these larger tyres, owing to the possibility of advantage being taken of the opportunity of overloading, which would over-stress the rear axle. However, if this matter be properly supervised and you wish to proceed with the change, you would require new wheels of at least 51-in. offset. You may be able to obtain these either from Sankey or Dunlops. The tractive effort would be reduced by 6 per cent., and this would have an appreciable effect on the pulling powcr of the vehicle. As regards the speedometer, this would read approximately two miles " slow " at 30 m.p.h.—ED.] GUIDANCE ON CONTINENTAL . TOURING

NEXT year I hope to be able to travel on the Continent as a coach driver for a well-known London concern. Could you therefore advise me as to the best books to purchase to obtain information regarding road signs and general rules on the Continent

I have enjoyed your paper for many years, but would like to see in it a few more road tests

London, N.10. L.B.

[We think your best course, in order to obtain such information as you require, would be to contact the Automobile Association, Fanum House, New Coventry Street, London, W.I. It may be advisable to mention that we have recommended you to do this. The Association has had great experience in connection with Continental travel. We are glad to learn that you have enjoyed this journal for a number of years. As regards road tests apart from difficulties in obtaining sufficient paper for their inclusion, the vehicles themselves are in such urgent demand that they can seldom be spared for the time required, but arrangements are being made, and more tests will be published shortly. There is, in fact, one included in this issue.--Eo.] IN the previous article l began to discuss certain items in " The Commercial Motor" Tables of Operating Costs Which have from time to time been the subject of controversy". 1 dealt with all the standing charges, ending with a long dissertation on the final item, interest, that being one 'which has been hotly disputed for as long as I can remember.

In the five items under "Running Costs" it is the last one, depreciation, which has most frequently been the subject of argument, and I shall deal with that in this article. Before doing so, however, I would like to take the other items in order, as there are one or two points that sometimes arise in connection with them.

On fuel cost I should like for a moment to digress and refer to the results of some experiments carried out by Leyland Motors, Ltd. Tests were made in the fuel con-. sumption of the 9.8-litre oil engine, which has been recently introduced to replace the 8.6-litre and 7.4-litre engines. The point under coasideration was whether the increased consumption of a larger engine would militate against its favourable reception by operators, notwithstanding the fact that on other grounds it would be more suitable.

Engine Size and Fuel Consumption As the result of these tests, it was found that the variation in fuel consumption m no case amounted to more than 4 per cent. Sometimes the advantage was in favour of the smaller unit and at others the larger engine showed at best. The additional power would, therefore, make no substantial differences to economy unless the vehicle were " driven frantically," as Mr. S. Markland, a director of I.eylands, put it.

The crux of the whole matter is, of course, in the last sentence. When I read it I recalled the number of times had trundled along behind a Leyland sixor eight-wheeler, comfortably cruising at double its legal speed. It occurred to me that that was what might be called by Mr. Markland " driving frantically."

This point has a bearing on the subject of this article, for hard. driving does increase fuel consumption per mile. I am willing to admit that this excessive consumption is not necessarily extravagance. The saving of an hour or so on a 200-mile journey, carrying a 12-ton or 15-ton load, may, in the gross economy effected, more than offset the extra cost of a gallon or so of fuel expended on the journey.

This is not to be interpreted to the effect that I am suggesting that operators should consistently break the law by exceeding the speed lima. What I mean is that operators who, using these Tables as a standard of comparison, find that their fuel costs are excessive, should appreciate that those who make the utmost use of the power of the engines in their vehicles for speed must be willing to accept increased fuel costs per mile.

Paying for Speed It is just as well to add that the same remark applies to all the items of running cost, especially to oil, the consumption of which per mile, especially in a part-worn engine, rises rapidly and out of proportion to the speed. Tyres, too, wear out much more.quickly at high speeds, and obviously tyre costs per mile are likely to be high when vehicles are worked under such conditions.

"The Commercial Motor" Tables do take such conditions into account, because the figures embodied are collected from all kinds of user and, therefore, must include a reasonable proportion of those whose drivers habitually drive their vehicles fast.

That is why, for example, although I know that the average figure for fuel cost of a 6-ton oiler, according to the Tables, is about 154 m.p.g., I am not surprised to hear of operators who get 18 m.p.g. or even 20 m.p.g. out of vehicles of that size and type.

Tyre cost is still a problem. Part of the difficulty I have in obtaining representative average figures for cost of tyres arises from the fact that synthetic-rubber tyres suffer badly from ill-use—more so than natural-rubber tyres—and the result is to increase cost variations as between one user and another.

I recall that in a recent article I pointed out that whoreas one operator assesses his tyre costs at 24d. per mile, another, sung similar vehicles and operating under similar conditions, gives me a figure of less than Id. per mile. Whenever, of

late, I have written and -expressed the view that tyres are improving and that mileages per set are increasing, I have had a spate of correspondence from operators who disagree. Yet I know, from general observations and from my contacts, that I am right.

In the forthcoming issue of the Tables I have, in a sense, compromised. 'lyre prices, as between the previous issue and this one, have increased by 20-25 per cent. So far as my figures show, tyre mileages have also improved, although, perhaps, not to the same extent. I am looking to the future and trying to make the figures in the Tables cover as long a period as is practicable. I have, therefore, split the difference, and left the tyre cost per mile as before, notwithstanding the increase in the purchase price.

I am sure that a rapid return to pre-war experience of tyre users is coming and with that in view I feel justified in assessing tyre cost on future probabilities, rather than on the recent past.

It is rarely that I obtain comparable figures for the cost of maintenance as I understand it—that is, obtaining figures which cover the cost of every item. The amounts quoted in the Tables are meant to be comprehensive in that sense, and they may seem high to those whose cost figures are not complete, according to my interpretation of the term. 'The consequence is that I sometimes get criticisms that maintenance costs, as given in the Tables, are high. The reason, I usually find, is that the critic has not debited maintenance with all the expenditure which, in fact, should be so debited.

Depreciation Is a Running Cost

Finally, we come to depreciation, the biggest bugbear of all. First—the point which is most often argued—should depreciation be regarded as a standing charge or a running cost? I have, from the start, placed it in the latter category, and have never yet heard any argument sufficient to move me from that attitude.

These tables of costs are prepared and intended to be utilized in a practical way. They apply to vehicles which are operated in this manner—that is, run for as Jong as it is economical for the owner to run them, and then discarded. The termination of the useful life comes when the machine is so worn that the cost of maintenance, and, more important, the cost of loss of use because of increasing frequency of need for repairs, become too high. Rarely is a vehicle replaced just because it is four, five or six years old. It is mileage which wears a vehicle out. It is mileage which must logically be the measure of its depreciation.

One factor of practical use, which seems to me completely to dispose of the idea of assessing depreciation on a time basis, is the wide variation in annual mileage, Compare two cases of use, one in which the vehicle covers 250 miles per week and another 1,000 miles. If depreciation be assessed at, say, five years, the first vehicle becomes due for replace meat after it has done only 62,000 miles. The other, apparently, is expected to run for 250,000 miles. Neither method is correct. If they be assessed on mileage and given 125,000 miles each, the first one will last 10 years, the second 21 years.

The first vehicle will, in normal times, have become out of date before it has run the 125,000 miles. Whether the owner is likely to be concerned on that account must depend upon the nature of his business. If it be such that his vehicles must be up to date, he will have to replace it at the end of five years, or, at the most, six years, in which case the assessment of depreciation on a 125,000-mile basis will obviously be wrong.

On the other hand, it is unlikely that the vehicle operated as described in the second case will last the 250,000 miles which it would cover in its five years. If it be kept in service for all that time, it will certainly be costing more than is economical.

Allowance for Obsolescence In preparing figures for the Tables. I make some allowance for vehicles operated over particularly low mileages, to deal with this "obsolescence," in the figures which I give for depreciation, assessing it as a running cost. In the case of a. light machine with an average life of 100,000-120,000 miles, I take the limiting figure of 24,000 miles per annum. If that mileage per annum be exceeded, the depreciation figure assessed on the life quoted is left unaffected. If the annual mileage does not reach that figure, the assessment for depreciation on a mileage basis is decreased by some percentage which grows as the annual mileage decreases.

Suppose that a 4.5-tanner costs £640 new. Deduct the cost of a set of tyres—say, £85—giving a net figure of £555. Assume that the residual value—that is to say, the price which the owner gets for it on the second-hand market when he disposes of it—is approximately 10 per cent, of that net figure (£55); then we have a net amount, on which depreciation is to be calculated, of £500. On a life of 120.000 miles, depreciation costs jcl. per mile. So long as the annual mileage is 24,000 or over, that Id. stands, If it be less—say, 20,000 miles' per annum—approximately 10 per cent, is added to the depreciation figure, bringing it to 1.1d. per mile.

The heavier types of vehicle can usually be given a much longer life than the lighter types and a usual figure is 200,040-240,000 miles. In the case of vehicles of that class. the amount ,for depreciation directly assessed stands so long as the mileage is 48,000 per annum or over. If below that figure, a corresponding percentage is added.

Operators who take five years as the period over which to depreciate their vehicles, normally use the original purchase price—in the above example, £640—as the basis of assessment and divide by five (giving an annual amount of £128 as the allowance for depreciation). If the mileage be 24,000 per annum, that is equal to I.28d. per mile. If it be 20,000 miles per annum, the depreciation is I.54d., and if only 10,000 miles, more than 3d. per mile.

The point that I want to make is that, in the case of a compilation such as " The Commercial Motor" Tables of Operating Costs, where we are concerned with averages, the assessment of depreciation as a running cost is the only practical method which meets all the needs of the case. .

I do not, in taking this attitude about depreciation., overlook the fact that the company's auditor will expect depreciation to be presented in a manner altogether different from that, and will certainly be taking time as a basis. He will depreciate the value of the vehicles on a percentage basis, taking depreciation each year on the value of the vehicle as it stands at the commencement of the financial year. An example of this is shown in Table I, where I have assumed that it has been agreed to depreciate the vehicles at the rate of 20 per cent. per annum, In the first year the depreciation

on an initial purchase of £640 is £128. The value is diminished by that amount for the second year and becomes £512. The depreciation for that year is assessed at £102 and the same procedure followed in each successive year.

Sometimes the depreciation is assessed at 25 per cent., for which the corresponding figures are given in Table Now come back to our discussion of one of the principal uses of the Tables, which is to assist hauliers, by assessing an average cost per mile, to quote rates and ch4rges. What a muddle they would be in if they tried to fix and stabilize rates on the basis of depreciation assessed by these methods. If they worked to Table I, and assuming that a vehicle ran 24,000 miles per annum, they must make allowance for depreciation in the first year at 128d. per mile, but in the second year at 1.02d. per mile, and in the fifth year at just over id. per mile.

If operators worked to Table II, the position would he even worse, because they would start in the first year with an allowance for depreciation at 1.6d, per mile, dropping to id. at the fifth year.

Finally, to settle the argument, take the case of depreciation being arranged to meet the requirements of the incometax assessor. This year, there is, as has been described, an initial allowance of 20 per cent., as well as a normal wear and tear allowance, which, in the case of A licensees, is 31i per cent., and, in the case of B, C and passenger-vehicle operators, 25 per cent. The figures for depreciation, in the case of an A licensee, assuming again that a vehicle costs £640, are set out in Table III. Here the operator would be expected to charge his customers 3.28d. for depreciation during the first year, but only id. in the fifth year.

It should be clear that for the purposes of the Tables, and, what is more important, the uses to which operators put these Tables, the only practical way to assess depreciation is on a mileage basis. S.T.R.


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