Solid-rubber Tires for Heavy Loads.
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Lower Prices in the Rubber Market Render the Use of Steam Wagons with Rubber-shod Wheels a Commercially-practicable Course.
Manufacturers of indiarubber tires are faced by a difficult problem, when they set out to convince owners of the lighter types of steam wagons that such treads are commercially admissible. Whatever may have been the trouble with tires and wheels in the years 1897 to 1902, improved methods of construction and maintenance have practically eliminated from the expenditure account any appreciable item in respect of wheels and tires, at least in comparison with the figures which were by no means uncommon six and more years ago. The hydraulic press in respect of the artillerytype wheel, the more general use of composite wheels, the advance in the quality of cast-steel wheels, and the adoption of more generous proportions in conformity with the scope allowed under the provisions of the Heavy Motor Car Order, 1904, are favourable conditions each of which has had its effect in the direction indicated.
Arguments in Favour.
Nothing can be said in favour of indiarubber tires if one's consideration of their claims is limited to the single factor of first cost or mileage cost. It is only when an owner of modern road plant, or a prospective buyer, is prepared to give due weight to the performance side of the log, that the peculiar advantages of the solid-rubber tire begin to assert themselves. First and foremost is the inherent merit of silence in running. No manager or engineer of a carrying company, who is in direct touch with roadside incidents, can occupy his position for many months without being made painfully aware of the troubles that follow upon noisiness in service, especially if his vehicles have to travel during the night. Well do we remember the experiences of the postal officials, when the first motor parcel mail service—that between Liverpool and Manchester—was inaugurated in the year 1902, and the flood of complaints which poured into the authorities, from inhabitants along the line of route whose slumbers had been disturbed by the rattling and impacts of steel-shod wheels, and it was not until rubber was substituted for steel that the hotly-worded epistles ceased. Many examples of this character might be given did space permit.
Now, the necessary corollary to noise is undue wear, and numerous records show that, whilst the running cost of rubber tires now varies between rid. and 2icl. per mile for vehicles with total weights of from 44 tons to 8 tons, anybody who is looking into the matter must give due credit for the savings which are effected in repairs. It is not suggested that these savings equal the additional outgo on the rubber tires, but they seldom effect a credit of less than 30 per cent, of such cost. It is, however, in point of speed and performance that the rubber tire proves its worth, where something more than an average of five or six miles an hour is essential.
Greater Speed and More Ton-miles.
There is no occasion to presume that every wagon without steel-shod wheels is strictly kept down to the legal average of five miles an hour on the road : where roads are open and of good surface, a reasonable latitude is generally allowed and utilised. None the less, in spite of these small extras, it is a well-used wagon that averages 250 miles per week, and that is under load for an average of 6o per cent. of its total mileage. Some wagons, of course, do much more than this 750 net ton-miles of work per week, as in cases where trailers are hauled, but the performance named is a fair criterion. Let us turn, next, to the requirements of the individual owner who wants quick delivery, and who is content to have a load of three tans instead of five. According to the provisions of the Motor Car Acts and the Heavy Motor Car Order, a steam vehicle for that load may travel at 12 miles an hour, instead of five miles an hour, if the weight on any axle does not exceed six tons, and so long as all the wheels are fitted with " pneumatic tires, or with tires made of a soft or elastic material." It is here that the rubber tire has its chance, because its use, when there is only two-thirds of the more customary load as one factor in the performance of the vehicle, as compared with the steel tire, requires only a speed of 8t, miles an hour to yield the same result. In one case, we have a maximum of five tons at fivc miles an hour; in the other case, we hay* three tons, or even more than that as a maximum, at 12 miles an hour. The product in the first case is 25, whilst it is 36 in the other.
Reckoning the Cest.
The case thus presents itself in a nutshell. The user whose conditions of work are not met by loads of less than five tons will do well, for the present, to wait until the rubber tire has been developed a little further than is the case at the moment. On the other hand, brewers, millers, mineral-water manufacturers, contractors and others to whom the advantage of the transport of a three-ton or even a four-ton load at so high a speed a's 12 miles an hour is appreciable, have no occasion to hesitate one day longer.
The vehicles will thereby be enabled to travel nearly double the distance per working day, and to maintain such mileages without knocking themselves to pieces, or being a palpable nuisance to the community. Further, whereas a live-ton lorry may cost, inclusive of all charges and deprecia tion, anything between and .4;8 per week, the lighter lorry with its rubber tires, and for double the effective mileage, will cost on the average only an additional 50s. a week net. We leave it to the likely purchaser to decide for himself whether the ability to get one or more extra journeys per day is worth the difference of, say, tips.
Sections and Prices.
It has fallen to the lot of the motorbus to help tire makers to determine the correct mixtures of rubber and the appropriate degrees of vulcanisation. The same hard tests have taught them how to choose sections which will not induce splitting through excessive oscillation, and which will not involve wasteful sacrifice of unused rubber when wear has brought the working tread close down to the flanges or thus; they also know, now, how to prevent any creeping of the tire round the eelloe. Tens of thousands of pounds sterling have been spent in the securing of that volume of practical experience which alone counts in commercial work, and the owner of the steam wagon for all loads between two and four tons may at once benefit by those losses and the lessons they have taught. For example, whereas the cost per mile for the rubber tires of a doubledeck motorbus was no less than.4d. a mile fiv.e years ago, the ascertained cost has gradually fallen, notwithstanding the severe conditions of use in consequence of the frequent stops, to id. a mile, and is still falling.
It remains only for us to give the ranges of prices for
different typical sections. A minimum width of four inches is advisable for vehicles which weigh between five and six tons inclusive of load, and a set of six such tires will cost about 413o; at least five inches in width and about are the figures for total loads of seven to eight tons; whilst, in the case of some progressive makers, six or seven inches in width and about Li to carry total loads of as much as 12 tons. The practice is to fit twin tires to the driving wheels, and there are small extra charges for rims, but the life of the material is sufficient to make the maintenance figures come within the range that we have quoted above—i*d. to 24d.
per vehicle-mile—for total loads not in excess of eight tons.
It is of great import
ance to follow the maker's advice as to the sizes to be used, and any of the tire manufacturers whose announcements appear in our advertisement pages will be
happy to give all par Section of the latest Peter Union itiocuril.ars on applica4942 5 q e L
tire for steam lorries.