Solving the Problems of the Carrier
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Tyre Costs and Tyre Care
Some Up-to-date Figures for Tyre Costs, Showing the Increase in Cost Per Mile as From 1939. Hope for Better Tyres Forecast in An Interview With Officials of the Dunlop Rubber Co., Ltd.
READING a report of question and answer in Parliament relating to tyre costs reminded me that I had in preparation an article on that subject. It will be interesting to begin with a reference to what transpired in the House of Commons.
The Minister of Supply was asked whether he was aware that the average cost of tyres to the transport department of Nottingham Corporation had risen, since 1939, from 0.199d. per vehicle-mile to 0.87d., and, in view of the high profits made by tyre companies, what steps he proposed to take to prevent manufacturers from charging needlessly high prices to consumers.
In the written reply, it was stated that transport undertakings obtained their tyres either by purchase or on a mileage basis, The purchase price of giant tyres was higher by at least 80 per cent, on pre-war figures, on account of increases in costs. These increases have had the approval of the Ministry. The second method, which is that followed by the Nottingham Corporation, included not only the supply, but also the inspection, servicing and replacement of tyres by the manufacturer. Costs in this direction had risen more steeply because of such, factors as the lower lasting qualities of synthetic rubber and the consequent need for reore frequent replacement. Arrangements on this basis were not subject to scrutiny by the Ministry, but it was, of course, open to any local authority to purchase its tyres if it preferred that system.
The curious part of that reply is that, according to this M.P., the lower lasting qualities of synthetic rubber appear to affect only tyres paid for according to the second method, which hardly seems logical. However, the point that really interested me was that the increase in cost, as experienced by Nottingham Corporation, confirmed my own frequently reiterated view that tyre costs had risen to four times above pre-war level. In this case, as can be seen, the increase is in excess of that.
It was, in fact, that statement of mine, and one other, to which I shall refer, which brought about a meeting between myself and two experts, Mr. W. Parsons and Mr. Lambourn, officials of the Dunlop Rubber Co.' Ltd. The former is head of the Service Department, the latter of the Technical Department. We met to discuss this matter of tyre costs per mile.
In the first place, objection was taken to a statement made in one of my articles that tyre costs had actually increased eight times. As a matter of fact that was not my own opinion but was, as I said in the article, a statement which had been made by someone else. I did, however, adhere to my view that, in the majority of cases, tyre costs per mile are approximating to four times what they were before the war, and I quoted average mileages of 8,000 to 9.000 per set, as compared with 22,000 to 24,000 in pre-war days.
Mr. Lanabourn stated that, according to his company's own technical data, present-day synthetic tyres should give a mileage equivalent to 70 per cent.—given similar operating conditions—of tyres which were produced pre-war. The increase in the purchase cost was 55 per cent., so that, if the figure of 70 per cent., of what I might term wearability,
Vehicle Capacity Tyre Size . No.of Tyres per Vehicle Tons 1 2 3 5 6 7-8 12 15 Ins. 30 x 5 32 x 6 32 X 6 34 x 7 36 x 8 36 X 8 36 x 8 36 X 8 4 4 6 6 6 6 10 12
be accepted, then the preSentzday cost of tyres per mile should be little more than double the pre-war cost, and not quadruple as 1 suggested. It was pointed out that if my figures be accepted it would mean that present-day tyres were giving only 38 to 40 per cent of the pre-war mileage under equivalent conditions.
Mr. Lambourn also stressed the fact that there were four factors outside the control of manufacturers, which had an important bearing on tyre costs per mile, namely, efficiency of maintenance of the vehicle, the speeds at which it was operated, the loads it carried, and the road surface's over which it operated. I accepted this, but suggested there was no material difference in the majority of cases, except possibly in connection with vehicle maintenance, as between pre-war and present-day conditions. Moreover, the difference in the efficiency of maintenance in respect of the vehicles for which I had information was not sufficient to affect the wear of the tyres to anything like the extent indicated by the cost-per-mile figures, which I obtained from the same sources.
It was then agreed, and this I think is particularly important, that poor conditions of operation, in respect of all these four factors, would have a bigger effect on synthetic tyres than on pre-war tyres, in so far as diminishing the life was concerned. It seems to me that, possibly, there is a good deal in that, as being liable to decrease that figure of 70 per cent. of expected life.
Incidentally, it was mentioned that the figure of 70 per cent. applied only to giant tyres, and that so far as car tyres were concerned the Dunlop figure for expectation of mileage for synthetics was 85 per cent, of pre-war mileages. 'In the course of the discussion I referred to trouble with tubes and gave instances of some which had burst within a very short time of leaving the garage where they had been fitted.
On this point Mr. Parsons was emphatic. He said that trouble with synthetic tyres arose almost invariably because they were not fitted in accordance, with instructions, and it seems that it would be an excellent thing for me to pass on the recommendations relating to the fitting of these tubes.
In so far as tubes which are fitted to wheels of flat-base rims, with flaps, the following precautions should be taken:—
(1) Dust the inside of the cover evenly with French chalk.
(2) Inflate the tube until it begins to round out; then insert in cover. (3) Make sure the tube is evenly distributed and free from wrinkles. (4) Apply a frothy solution of soap and water generously around the entire base of the tube, extending upwards between the tyre beads and the tube itself for at least 2 ins, on both side. Also apply the solu tion to both sides of the flap. Do not allow solution to run into the crown of the tyre. The soluticn must be strong enough to feel slippery when the fingers are wetted with solution and rubbed together. (5) Insert flap, making certain it is centred between the beads and that the edges are not folded over. (6) Mount assembly immediately on the rim while soap solution is still wet, and inflate to correct pressure.
The foregoing procedure must be followed, without fail, whenever a synthetic tube is fitted. In an emergency, French chalk may be used as a substitute for a soap solution, provided it be evenly and generously applied. The use of French chalk in this way as a general practice is, however, not recommended.
I have heard operators scoff at this idea of using a soap solution when fitting inner tubes. In view of the emphatic insistence of Mr. Parsons on the importance of this solution, it seems likely that some, at least, of the complaints I have heard about failure of synthetic tubes is due to operators having deliberately ignored this recominendation.
Whenever synthetic tubes are being repaired, the punctures or injuries should be vulcanized. Ordinary patches should be used only for emergencies.
A similar set of instructions with slight modifications is issued in connection with well-base rims.
During the course of our conversation, I asked what were the prospects of improvement in connection with synthetics and, particularly, of a return to natural rubber for tyres which would be on the market and purchasable by hauliers.
The position as regards tubes is that there is already a certain amount of natural rubber in the tube mix. Although it is probable that tubes will go right over to natural rubber earlier than covers, it is not known when this will be.
I gathered, unofficially, that tyre manufacturers will be almost as pleased as operators when the complete return to the use of natural rubber becomes practicable.
One point arose, however, which should be kept in mind by those whose interest in their vehicles goes a little deeper than loading them, running them, and unloading them, and that is in respect of tubes made. of a particular kind of synthetic rubber known as GR.I (Butyl). It appears that for tubes themselves it is a good substitute for natural rubber and from one point of view, i.e., air-holding properties, it is actually better than the natural rubber.
Apparently, these GR.I tubes will hold the pressure much longer and thus eliminate the need for such frequent inflation. That, however, is a point which is of only passing interest as this material does possess disadvantages and is unlikely, at least for some time to come, to be standardized for tubes.
One point• about synthetic tyres emerged which was a surprise to me and will probably surprise most readers, namely that vehicles on synthetics are likely to use more fuel than vehicles on natural-rubber tyres. The increase is small. The reason is as follows : All pneumatic tyres, whether made of natural or synthetic rubber, absorb a certain amount of energy when they roll on a road surface under load. Rubber is not a perfectly elastic substance; hence, when it is deformed by an external force, some of the energy is absorbed by internal friction in the rubber and it i§ this energy absorption of a tyre that causes it to warm up. The amount of rolling resistance or energy absorption of a tyre varies considerably, depending not only upon the tyre construction, but on the operating conditions as well. Synthetic rubber is less elastic than natural rubber, although efforts are continuously being made by the tyre industry to improve this property. Therefore, syntheticrubber tyres will have a higher rolling resistance than natural-rubber tyres, the amount of increase depending on the proportion of synthetic rubber in the tyres.
Vehicles equipped with tyres made of present-day synthetic rubber require slightly more power to offset the increased rolling resistance and hence their fuel consumption is greater. The exact increase will vary considerably with various types of vehicle, roads, loads, speeds, inflation pressures, stopping and starting, and wind conditions, and for these reasons it is difficult to make a definite statement relating synthetic tyres with fuel consumption.
The effect of fitting synthetic tyres is relatively small,
however, and it is obvious that fuel-consumption tests, comparing natural-rubber and synthetic tyres, must be carefully carried out and assessed in relation to actual operating conditions. In making direct comparisons, it is most important to ensure that new natural-rubber tyres be compared with new synthetic-rubber tyres and to employ identical testing conditions.
Increase, 1939 to Now Tyre Cost Per Mile Percentage
Tests ieported to date indicate that the increase in fuel consumption may amount to between 2 per cent. and 10 per cent., a range illustrating the effect of the variables mentioned above.
For the purposes of calculation, an average increase in rolling resistance between natural-rubber and synthetic rubber tyres of about 10 lb. per ton may be taken; i.e., for a vehicle weighing 8 tons this would mean an added rolling resistance of 80 lb.
As a corollary and as a supplement to this discussion • about synthetic tyres I have compiled the figures which appear in the accompanying tables. They are, I think, selfexplanatory, except as regards those which relate to 6-tonners, and for that type of vehicle some further comment is necessary. In Tables I and II I have assumed that 6-tonners are fitted with 36-in. by 8-in. tyres. That, unfortunately, is not a universal practice. Perhaps a fairer way to put it would be that vehicles which are habitually loaded to six tons are fitted with 34-in. by 7-in, and not 36-in. by 8-in. The reason is usually that the vehicles have been sold to carry five tons with an occasional overload to six tons, but are used habitually to carry six tons with an occasional overload to seven tons. Without a doubt 34-in. by 7-in. tyres are insufficient to carry that load. Moreover, as has already been stated in this article, the effects of overloading are much more noticeable with synthetic tyres than they are with natural-rubber tyres.
Now, in pre-war days a set of 34-in. by 7-in. tyres on a 6-tonner would cost £65 7s. They would run on an average 18,000 miles, giving the cost of 0.69d. per mile. A set of 34-in. by 7-in. involves to-day an expenditure of £85 Is. and the operator will be lucky if he gets 8,000 miles out of them, so that his cost per mile is 2.55d. Actually, many operators tell me that they regard 6,000 miles as a fair expectation of life from 'these tyres, which is equivalent to a cost of 3.4d. per mile. S.T.R.