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Overloading and Overdriving.

20th April 1911, Page 3
20th April 1911
Page 3
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Page 3, 20th April 1911 — Overloading and Overdriving.
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Which of the following most accurately describes the problem?

By Henry Sturmey.

The performances of cars in commercial use vary considerably, and one is often at a loss to account for the differences. Here are two cars, both turned out of the same factory, all parts made of the same material and by the same tools, and interchangeable with each other ; and yet, whilst the owner of one speaks in the highest terms of satisfaction of his vehicle and reports a perfect service, the owner of the other will tell you that it is not altogether a success,. that it is often out of service, and that the repair bills are .heavy. What can account for the differences There must be some reason, and it does not necessarily follow that the cause of the trouble in the one case is necessarily inherent to that particular car. Nor does it follow that the cause is unpreventable. Indeed, all reason points the other way, and, if the matter is carefully gone into and all details of work ing the two vehicles are analysed, the cause of the trouble will almost invariably be found in the way in which the two vehicles have been driven and cared for. Where the car is properly designed and well constructed in the first place, a failure to-day to get

satisfactory results may be almost invariably traced to the management—or lack of it. Comparison has, before .now, been made between the service which is obtained from a motorcar and that from a railway engine ; but members of the public, who make such comparisons, do not know what goes on in the rail way-engine shed. In the first, place, the conditions of running, always on a specially-prepared bed, and almost always at a practically-uniform speed, are an ideal for satisfactory service, whilst, the conditions finder which a motor vehicle has to work I mean the conditions of traffic, grade and surface—are very much the other way about. Again, it is a certainty that not one car in ten gets the same, regular, careful systematic attention which the railway engine gets. If they did, we should hear very few, if any, tales of unreliability.

Troubles with well-built vans and wagons can, apart from lack of attention in the garage,_ be almost invariably traced to two causes : overloading and overdriving. For the first, the owner is often even more responsible than the driver, and the latter is of course entirely a driver's delinquency, although here anent the owner, by setting his man too close a timetable and making no allowance for stoppages, may sometimes be the responsible party. On the score of overloading, the purchasing business community finds it apparently—at least such is my experience— very difficult to grasp the fact that a motor vehicle is designed and constructed to carry a certain specific maximum load, and that any overloading beyond t his maximum figure is subjecting all the mechanical y-arts of the ear to stresses beyond those for which their constructional calculations were made. With their horse-drawn vehicles, few owners know the w eights of the loads which are taken. They know, for instance, that a two-horse wagon does a .certain amount of work in the way of shifting a certam.number of units or packages common in their business, but, if you ask them the weights of the load their wagons carry, they are often hopelessly and ludicrously at sea. A few days ago, for instance, T.ealled on a firm of brewers and retail beer and mineralwater people, who were wishful to discuss the motor question. I asked them what loads they hati. to carry, and they said they thought a 10-cwt. vehicle would be all they would need. Thinking this was rather small, in view of the character of the businlss done, I inquired further, and the man in charge of the traffic ciepartment was called. fie was asked the weight of loads taken on a particular journey, and he could not say. 1 here were, as a rule, so many barrels. When asked the weights of the barrels, he

had not the remotest idea : He could, of course, give me the number of gallons per barrel, so that the calculation of the contents was an easy matter, but as to what the weight of each barrel was he could not say. The particular load on this journey was admitted to be nearer two tons than 10 cwt. ; then,

when it came to discussing the loads to be dealt with in the bulk of the shorter journeys, he was asked about a particular one, one of the directors, " supposing " that " half a ton would cover this," was told that the usual load for that round was 46 to 56 cases. But what a " case" weighed, none of them could tell me. This is by no means an uncommon or unusual experience, and, when it comes to the men who have charge of the loading, it is usually a case of " Oh ! shove it up ; there's room" ; so long as there is " room," dead weight doesn't matter ! But it does, very much—to the car.

Tires are calculated to carry certain maximum loads, including car and contents. Springs, likewise, are graded to the maximum loads the car is designed to carry, chassis frames are of depth and thickness for the work they have to do, and axle strengths and wheels are likewise calculated for the same maximum-load work. I believe that in some eases—indeed, I have had one instance in my own experience about which there. was no dispute—owners are shortsighted enough deliberately to buy a wagon below not only their maximum but their average load capacity. And they pride themselves upon being " ,smart! " Such, at any rate, was the case in the particular instance I have in mind. Seeing that the next-size wagon cost another £40, although that was the size—even rather under the size—best calculated to meet his needs, he purchased a smaller vehicle, and asserted that, although his loads were greater than the load capacity of the vehicle, " it would carry them all right." He knew !

Manufacturers naturally allow a certain " margin of safety." If they did not, some '' clever" people would be in difficulties from the first day of using, but it is unfair and unwise to the vehicle to rely on that. A small overload upon occasion may not do any harm : the car won't break dawn under it. But, should it be found absolutely necessary to carry an overload, the pace should be reduced. It does not necessarily follow that the load will automatically

reduce the pace, because most modern vehicles today have a surplusage of power for work upon the level, and on level ground a few cwt. more or less makes little difference to the pace obtainable, but it does make considerable difference to the stresses thrown upon the various parts of the car. The effect of road shocks, such as are imparted when passing over a rough road, vary at lowest as the square of the speed of the vehicle, so that the careful and considesate driver, if he has to take an excess load, will reduce his speed rate while he has it on board. This brings me to the question of overdriving.

• The statements I have. jusL made, to the effect that the destructive effect of road shocks is increased at lowest as the squaSe of the speed of travel, will be quite sufficient in itself for the thinking man. A couple of years ago, I was speaking to an owner of a couple of ten-year-old vans, and lie expressed himself as perfectly satisfied with them. Asked if he ever had any trouble with them, he admitted that "at first 'that is for about seven years—he had had some trouble, and their service was not entirely satisfactory, but, he added, "for the last, three years we have had a couple of good men, who take a pride in their machines, and we never get any trouble now." I have not the slightest doubt that the pride of the men in keeping their machines in proper fettle was not by any means limited to careful looking after them in garage, but was evidenced in careful and considerate driving on ale road. The importance of careful driving and of reducing speed over rough places cannot be too strongly impressed on drivers, especially on new men, who can hardly be expected to have the knowledge which will enable them to argue the matter out for themselves. " If the car will go the pace, it is all right. If it isn't all right, why does the maker make it so that it will travel at a destructive rate," seems to be. the argument, if there is any

argument used at all. But the exhilaration and pleasure of speed—for, although not a speed machine a. motorvan is three times as fast as a horse van— are often largely accountable for the transgression. In addition to this, there is the incentive, especially when making the last home journey for the night, of wanting to get back quickly and to get done for the day. Some cars are capable of travelling on a Level road as fast as a touring car, if the driver " lets her out," but, when it is remembered that the touring car carries a light. lire load, and that the shoeks are deadened and absorbed by pneumatic tires, whilst the commercial vehicle has much larger dead loads and far less shock-absorbing tires to run upon, it will be seen that the conditions in the two instances are totally dissimilar.

Drivers are not always entirely to blame for speed travelling, because the traffic master of the firm will

sometimes give them a time-table to work to which compels them to force the cars considerably, in order to keep anywhere near it, but I think in the majority of cases overdriving is due to the driver. it is not altogether an easy matter to prevent his doing so. One method, of course, is to govern the engine, but this is not entirely satisfactory. I will not go into the why and wherefore here, save to say that, for Erni reason that the system has its drawbacks as well as its advantages, tew manufacturers attempt it, although I believe I am right in saying that everyone ot them would do so coulu they lind a really-perfect system. For instance, I quote from a. letter I have before me at the present time, from the user of a number of cars fitted with such a device, in which the shop foreman in charge says : "We have had to abolish the governing gear on all the vans, since the honestly valve in every engine would assume positions quite independent of the governor.From this, it wound appear that it does not follow that because a ear is fitted with a governor that the governor governs correctly ; and I may add that this same firm of users is now trying a plan by which it lays out to govern the driver instead of the engine, and I am inclined to think this the more satisfactory method. It consists in fitting each car with a tell-tale speedometer. This was first suggested by me, and Messrs. Frodsham and Co. have now produced an instrument which fills the requirements of the situation. This consists in a speedometer, which not only shows by its movements the actual pace at which the car is at the moment travelling, and so enables the driver to regulate his speed, but which possesses what is called "a maximum hand," that is to say, there is a second .hand, moving forward over the face of the dial with tin-, indicating hand, but not moving back with it, so that, at the end of the day, this maximum hand stands ftxecluntil the traffic master at home releases it— at the highest speed the car has reached during the day's work. In this respect, the instrument is not singular, as most makes of speedometer are or can be provided with such a device, but where the instrument is singular, and where it is valuable, is that not only does it record this highest speed attained, but every time a certain set speed is exceeded it " scores one on the clock," so that, at the end of a day's work, the car master, by looking at, the dial, can tell at a. glance both the highest speed the car has been allowed to attain, and the number-of times the driver has exceeded the reasonable economical pace et which he has been 'instructed to proceed. A small fine for every time this pace has been exceeded will Drove about the best form of " governor " one is likely to get. There are also other recording instrutnents that may be fitted, which go much further than this and which, by means of a scale and travelling pencil, record on paper the actual pace at which the car has been travelling through every moment of ths day, but these instruments cost three times as much as the one to which I have alluded, and which, with proper organization and systematic checking, should he fully effective. I have not yet heard how the system works. but it may be taken as axiomatic that no heavy wagon—say above two-ton capacity— should be run at more than 15 miles an hour, or in a rough country, 12 miles, and that no solid-tired light van should be allowed to exceed 20. If higher speeds than this are considered a necessity, by reason of the nature of a 'firm's business, such as for instance in the case of newspaper work, pnemnatin tires must he employed. These are altogether too expensive for commercial usage, where expense is the first consideration, but the man who wants high sneed must be prepared to pay for it-he cannot have it both ends. Finally, if owners will give more-serious attention to these two auesitions of overdriving and overloading, they will find themselves substantially in pocket and in a better frame of mind about their motors at the end of the year.

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