USERS' VIEWS ON TYRE EQUIPMENT.
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Further Experiences of Prominent Owners. The Pros and Cons of Pneumatic and Semi-pneumatic Tyres Collated and Analysed. Surprisingly Good Results Obtained Under Service Conditions,
I N our issue of last week we were able to give some particularly interesting information regarding the employment of pneumatic and cushion tyres by various big users of passenger vehiclek, including some of the most important municipalities. Since then we have received further information on the subject and, after dealing with this, we will analyse the details obtained and append what amounts to a census of opinion regarding the tyres employed.
The Bristol Tramways Fleet.
We will commence with the experiences of the Bristol Tramways and Carriage Co., Ltd., which runs a large number of buses and coaches of its own make. There are two types, the 40 h.p. 4-ton chassis equipped with 30-seater bodies and the 30 h.p. 2-ton chassis carrying bodies to hold 20 passengers. The wheels are Dunlop standard tenstudded, of the dished-disc pattern and, in the case of the larger buses, the tyres are 38-in. by 7-in, singles at the front and twins at the rear; whilst on the smaller vehicles 34-in. by 7-in, single tyres are used all round. The reason for selecting this form of tyre equipment for all the vehicles
is the excellent results ob tained during long service experience. The roads are mostly tarmacadatn, fairly good on the town routes, but in the country some of the surfaces are bad. The 38-in. by 7-in. tyres average 31,000 miles and the 34-lia. by 7-in. 18,000 miles.
Immediately front tyres show signs of wear the wheels are transferred to the rear. This is for the reason, that worn tyres are more subject to puncture and punctures at the front are more likely to cause delays, apart from any trouble which might arise in connection with the steering of the vehicle; but pneumatic tyres have given very little trouble and there are no complaints of skidding, whereas, formerly, cushion tyres were employed and the drivers fre (Dienes reported this form of trouble.
All pressures are tested by gauge during overnight inspection, and it is found economical to provide ample and convenient facilities for inflation by electric power. No serious effects whatever have been experienced as the result of bursts.
The mileage between punctures during the first ten months of the year 1927 was 15,740 and tho mileage between delays 32,560--this is on the 30-seater buses. In the case of the 20seaters the mileage between punctures was 25,690 and, here, of course, the mileage between delays was the same because the vehicles could not continuo to run on their single rear tyres. A good margin is permitted to cover reasonable overload and, as pressures are carefully watched, the company has immunity from trouble due to overloading.
Much interesting information has reached us from Edinburgh, where quite a large fleet is in operation, for detailed particulars of which we refer our readers to the information on this matter which was contained in our issue of last week, which was a special number devoted to passenger travel. It will be sufficient here to refer to the fleet in general as consisting of single-deck buses seating from 29 to 32 persons ; six-wheeled single-deckers for 39 passengers; open-top double-decked buses seating 52 and 56 persons respectively ; and coaches seating 14, 27 and 32 people.
In Edinburgh all municipally owned passenger vehicles have, for some time past, been run on pneumatic tyres, which, undoubtedly, are much to be preferred. The experience of the municipality has been a very lengthy one and has amply warranted the adoption of this type of equipment. The air
cushion tyre was certainly a decided advance upon the earlier solid-band pattern, but is not to be compared with the pneumatic. There is not the least doubt that the following good points are largely—if not entirely—owing to the use of pneumatic-tyre equipment
(1) Elimination of vibration and of the innumerable complaints formerly
received from residents along routes traversed by the buses. (2) Decided economy in the maintenance costs of engines, chassis and bodies owing to the absence of vibration. (3) The braking effect on a 5-ton bus when equipped with pneumatic tyres is found to be much greater than that obtained on a similar vehicle equipped with either solid or air cushion tyres. (4) Skidding is much more in evidence with cushion tyres than with pneumatic. On a recent occasion it was necessary to withdraw from service, owing to complaints of skidding, a double-decked bus equipped with air-cushion tyres ; whereas on the same route pneumatic-tyred vehicles were able to carry on without any trouble. This may, of course, have been the fault of the particular tyres.
Tyre Cost in Edinburgh.
The roads traversed have surfaces of widely different characters. These are granite, or whin setts, tarmacadam, granolithic and wood blocks. The average mileage for the front tyres is 36,250 and for the rear tyres 32,510. For the year ending May, 1924, the cost of solid tyres was .84d. per mile. The coat of pneumatic tyres, including the price of the conversion sets of equipment, was found to be .954d. per mile for the year ending May, 1925, .924d. for that ending May, 1926, and .689d. last year.
It is considered that correctness of air pressure is vital to the prolongation of tyre life and, for this reason, the pressure of every tyre is tested nightly and any losses made good. The man on duty goes around each vehicle with a pressure gauge and wheels his portable electric air pump with him.
Bursts are practically unknown, nor is it thought that these need be feared in the slightest degree when straight sided pneumatic tyres are employed, as the tyre cannot leave its rim owing to the presence of the flange and locking ring; whereas this is not the case with the beaded-edge tyre. In one instance of a tyre burst the vehicle was empty except for our informant, and although it was a front tyre which went, the experienced driver did not feel any drag on the steering and, but for the noise caused by the burst, he would not have known that the trouble had occurred. The total drop from full inflation to deflation in respect of a 38-in. by 7-in. tyre is 4 ins., and, when examining this vehicle from the front it was not possible to discern any perceptible angle, or tilt, towards the punctured side.
No actual failures have been experienced with semi-pneumatic tyres, but they are not so long-lived as pneumatics.
The number of punctures in the whole fleet, calculated over a period of six months, has been less than one per day, and the delay caused in such instances is not pronounced. In Edinburgh the services are confined to the city boundaries and no spare tyres are carried. A driver reports a failure by telephone to the garage, when another bus is immediately despatched to replace that defective. The man who takes out the relieving vehicle carries with him a
spare wheel. He takes over the relieved bus, changes the wheels and returns with it to the garage. In the case of buses in which twin tyres are employed at the rear, they are sometimes run home in ease of puncture, but, in such instances, they must be empty.
Tyre-puncture Alarms.
What is of great assistance in the prolongation of tyre life in Edinburgh is the fact that every tyre, front and rear, is equipped with A puncture-alarm device. The normal inflation is between 75 lb. and 80 lb. and the device detonates a cartridge when the tyre pressure has fallen to 35 lb.
All tyres are -purchased outright, and, in view of the excellent quality of the equipment now manufactured, it would not he a paying proposition to purchase on a mileage basis. The system of tyre inflation is by means of portable electric pumps which are mounted on trolleys and can be wheeled to any vehicle in the garage, the connection being plugged into the nearest pillar.
Recently delivery has been taken of a Luchard air compressor, with the necessary portable high-pressure air 'cylinders.
Overloading at mealtimes and to and from football matches is somewhat pronounced, but so far it has been found that the pneumatic-tyre equipment in use is sufficiently robust to stand up to all calls upon it, and there have been no failures due to this cause.
Morecambe uses 36-in. by 6-in. tyres on its 32-seater single-deck buses and 34-in. by 7-in, on its 53-seater doubledecked six-wheelers. It has been foundthat pneumatic tyres are better able to resist skidding and are more comfortable than other forms. The roads are of good tarmacadam, except that a disused tram track runs along half the routes.
With the smaller tyres, those at the c42 front average 20,520 miles, and at the . rear 20,049; whilst the larger average 21,797 miles at the front and 19,040 at the rear. The cost of.the tyres is .773d. per mile. All pressures are tested twice a week, and, when required, are inflated from cylinders charged to a pressure of 2,000 lb. by a plant owned by the Morecambe garage. No serious effects have resulted from bursts. Punctures are infrequent. but, where they occur, cause a delay of approximately 15 minutes. When twin tyres are employed at the rear, the vehicles are run home on the good tyres in case of puncture. Tyres are purchased outright.
A test has been made of Pirelli semipneumatic tyres, alai lour of these have already run 34,000 miles on a Leyland double-decked bus and are still doing so well that they will probably reach 45,000 miles before being worn out.
The Information Summarized.
It is obvious from the experiences which were given in our issue for last week and others which we include in this that pneumatic-tyre equipment is giving almost universal satisfaction, and this at a cost very little higher than would he the case if solid tyres were employed. The reason for the obtaining of cost figures which are far more favourable than even the most optimistic would have dared to prophesy but a few years ago is that the average mileage obtained is much greater than was anticipated.
By collating the lives of the tyres on the fleets with which we have dealt, and taking an average, the result has shown that this average is approximately 28,000 miles. It must be remembered that it covers all classes of pneumaticl tyre equipment and all iypes of passenger vehicle.
Most of the figures obtained refer to the tyrea onall four wheels, as it appears to be a practice to change them over from time to time, but in the few cases where separate figures have been given, it is noticeable that the life of the front tyres is between 3,000 and 5,000 miles less than that of the tyres at the rear. It is rather interesting to observe that, in certain instances, front tyres, when partly worn, are transferred to the rear wheels, whilst, in other cases,
'Some Striking Figures.
The average cost of tyres per vehiclemile works out at .70d.; punctures average 1 in 30,110 vehicle-miles, and delays caused through such punctures average approximately 20 minutes for each case.
For replenishing the air-in the tyres electrically operated pumps and highpressure cylinders filled by stationary plant at the garage are used in about an equal number of instances of ordinary deflation.
In view of the fears expressed by certain scaremongers, it is of importance to note that in not a single ease has a burst tyre been the cause of an accident, even of a minor variety, • Air-cushion tyres are not used on
many vehicles, but where employed, whilst being considerably better than solid tyres, they do not compare very favourably with pneumatics, except in price, which, in one particular'instance, is given as .57d. per mile for the aircushions and .78d. for the pneumatics. One municipal user, however, found that buses equipped with air-cushion tyres could be employed without chains on macadam and asphalt roads coated with snow and ice—undoubtedly a re-, markable testimony.