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27th July 1920, Page 17
27th July 1920
Page 17
Page 18
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Which of the following most accurately describes the problem?

The Probabilities of the System Making Good.

By " Vectis."

WE ARE HEARING a great deal just now about the coming revolution in motor transport that is to be brought about by the general introduction of pneumatic tyres on commercial motor vehicles. The idea is, of course, an attractive one, but it is not afe to jump to the conclusion that the use of these tyres will be justified in the average case ; that is to say, when the decision rests entirely on straightforward considerations of economy.

Some, at least, of the difficulties in the way of designing pneumatics for heavy vehicles have been overdome, and we may fairly confidently look forward to their use, wherever the user has strong reasons for desiring either eiceptionally high speed capabilities or, alternatively, exceptionally thorough protection from the vibration due to the, minor inequalities on the road. The average trader will, however, ask the simple question of whether, if he fits pneumatic tyres, he is going to get his deliveries effected or transport performed More cheaply on that account.

Tine pr of the movement in the tnited States is not sufficient evidence for users in this country. The road system in America is very'different from our own, and it is eleaa-ly possible that pneumatics might be justified 092 one system, but an entirely unnecessary extravagance on the other. Again, we might find pneumatics becoming very popular in districts where sette or pave roads abound, but remaining comparatively rare on heavy vehicles where most of the roads are macadam or wood paved.

What is the Gain in Speed ?

At the present moment the law governing the use of heavy motor vehicles does not contemplate the employment of pneumatic tyres, and, consequently, makes no special provision differentiating in their favour. Thus, if we may assume that the user intends to observe the law as it stands, he can evidently Fet only a very small increase in avea-age speed by using pneumatics instead of solid tyres. The present commercial vehicles are all well able to travel under remsonably favourable conditions at the full speeds permitted them by law. Probably, when it comes to the revision of the law, the Ministry of Transport will be willing to permit higher speeds to pneumatie-tyred vehicles.

Let us consider, so far as we can, what will be the position if the pneurnatic-tyred lorry is allowed a speed-25 per cent, in excess of that permitted to the solid-tyred lorry of equal capacity. This authority to travel at higher speeds could not be practically utilized throughout the day. The fitting of pneumatics would, in itself, do nothing towards reducing time spent in effecting deliveries, in leading, or in unloading. A 25 per cent. tolerance might mean an average of 15 to 20 per cent, higher speed during running hours, but would probably not mean an average of more than 10 per cent, higher daily mileage in the average case. This increased speed and mileage could certainly be obtained without increasing the power of the engine, because of thp greater resilience and lower resistance to traction of the tyres. Probably, in fact, the occasions on which it would be necessary to open the throttle fully would be less frequent, and we might find that a 3-tonner which had been doing seven miles to the gallon would now do eight miles to the gallon. In that ease, and if we take fuel at its present price, we should be reducing the fuel cost to 4d. a mile instead of about eid. a mile. The pneumatics might also, despite the higher speeds, have the effect of reducing the repair bill per mile covered. We can hardly allow for a saving of more than d a mile on this score, or a Id. a. mile under the heading of fuels and repairs taken together.

Now, let us suppose that the total cost of operatics's' has been is. 4d. per mile, 10d. out of this amount being represented by running costs, and, 0d. by standing charges. The standing cost per mile, owing to the additional mileage covered, would be reduced by about 10 per cent, or, approximately, id. a mile. This gives us a gross fraying of lid. per mile due to the use of pneumatic tyres. It is just possible that we might increase this amount by employing a somewhat more lightly constructed and cheaper vehicle, on the grounds that the light structure will be sufficiently protected by the pneumatic tyres. On the other hand, the wheels and tyres themselves will cost more in the first instance, and, on the whole, I suggest that it is not safe to aseume any saving under the headings of depreciation or interest on first cost.

Thus we reach the conclusion that, if the legal speed limit for a heavy motor on pneumatics were 25 per cent. higher than for a similar vehicle with solids, the pneumatics would give the cheaper tramsport, provided that they did not involve an additional cost of as much as lid. per mile for tyre maintenanea Personally, I doubt whether they would rat involve a considerably higher figure than this. For one thing, they are more or less liable to damage against the kerb. They are also to some extent liable to bursts, punctures, and cute. It would certainly be necessary to have the pneumatics rerv-ulcanized or to fit new tyres before the set was really worn out, because, ip commercial service, we cannot take 'any risk of unpunetuality due to avoidable breakdowns on the road.. The tyres would certainly be expensive in the first place, and their life in miles would not compare favourably with that of solids. At least, I should be very much surprised if it does so. Thus, altogether, it seems very questionable whether, given a reasonable increase in legal speed and utilizing it, the pneumatic will justify itself economically on goods-carrying vehicles.

Economy in Running instead of Speed.

There is, of course, another line alohg which we might work. We might aim at no increase in speed, but merely at securing the same speed with lower engine power and a lower repair bill. This looks to me the more promising of the two methods. One can well imagine that a vehicle which has done seven miles per gallon on solid tyres might do, as much are nine miles on pneumatics, if fitted with a smaller engine and maintaining the same average speeds. Thus, we might effect an economy of as much as lid. a mile in the fuel bill. Meanwhile, we should certainly be protecting both the mechanism and the body from vibration, and we might score here ter the extent of 4d. or Id. a mila With comparatively low speeds, the pneumatics would last longer, Bo that the additional tyre maintenance cost per mile would be less. Also, there would be some considerable reduction in the cost of the vehicle, minus tyres, if it were fitted with a smaller engine and a transmission system adectilate, but not excessive, to transmit smaller engine power. Thus, I suggest that there would be no need for the law` to provide special speed limits for heavy motor vehicles pneumatic tyred. Economy of transport

would be best served by retaining the same limits as applied to solid tyred vehicles, and thisalso would be better for the roads, in view of which the pneumatic tyred machine might reasonably be given some advantage in respect of taxation.

. In all this argument we have been disregarding those special cases in which higher speed capabilities have particular value as permitting of a much-needed in -crease in the radius of action of the vehicles. These

cases we exceptional rather than general.-.

. Turning to the passenger-carrying vehicle,. we see that the whole case is essentially different, because here there is :an opportunity of increasing the takings per mile run. by charging higher fares in return for a greater degree of comfort. Apart from comfort, .the. .aving of a few.minutes of time may be sufficiently important to passengers to lead them to pay higher rates in return for it. On the other hand, an,improvement of 10, or even20, per cent, in speed would seldom result in securing for the owner of the vehicle higher

rates for the goods-carried, or higher prices for them when they reach the market. There are, undoubtedly, many districts in ,which services of pneumatic tyred passenger-carrying vehicles would be more successful financially than similar servIces conducted with solid tyred vehicles.

Thus to sum. up the whole position, it would seem that tile giant pneumatic is likely to, be given its first big practical tests in this-country, on a sufficiently large scale to be useful, in connection with passenger services. The data that will then become available will enable us to form a Much sounder judgment as to whether the use of these tyres can economically be extended to the generality of goods carrying vehicles. In the meanwhile as regards these latter, the best possibilities, as already indicated, do not appear to be connectea so much with increased speeds as with decreased consumption of fuel and the elimination of a part of the repair bill. The large-size pneumatic has yet to justify its extensive commercial use.


Organisations: Ministry of Transport

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