Motors and Motoring
The Modern Motor Car. III—Some Special Features
I HAVE previously laid emphasis on the fact that the motor car is fast heed-Ming an "object of interest to all users. It is remarkable how"-the ranks of the owner-driver are swelling month by month, and this is not only so in the case of those whose incomes are not large and entail the use of the smaller and less expensive types of car,)itit in that of persons who larger and more costly machies. Even the man who keeps several cars and seldom if ever drives himself now often takes an interest in the running and upkeep of his motors. Women, too, are beginning to play a large part in motor ownership and motor driving in this country, and this development will increase rapidly in the near future. It is for the above reasons that in these fortnightly motoring articles I am including occasionally a brief and - simple explanation of some of the special features of the modern motor car which are to be found in the majority of makes, and which are therefore of corre- spondingly wide concern. In the two previous articles the question of the number of cylinders was referred to, and crankcase ventilation, autovac petrol feed, thermostatic control of the water ternperature, three and four speeds, and servo assistance for the braking were mentioned. Here it is proposed to touch upon balloon tyres, centralized automatic or semi-automatic chassis lubrication, and automatic or half- automatic spark control.
The balloon tyres originally employed have undergone con- siderable modification. The _original pressures were on the low side, and the walls were -insufficiently_ strong. _ These faults were overcome, with the consequence that the reinforced medium-pressure tyre has been practically universally adopted for cars of all -nationalities and sizes, and to-day excellent all- round results are Obtained both as regards reliability and durabilitSr. -It 'is- ridiv no longer a matter of choice as to whether the new car owner should settle on high-pressure or low-pressure tyres, but I- am.often asked- what are the advan- tages of this newest form of coyer, and also what are its draw- backs. It May be of interest, therefore, if I briefly set these ord. The low-presaure- tyie has increased air volume corn- pared_with the high-presstrie-kindinnd -so-can be- run at a lower pressure. The cover is thinner and far more pliable, and with reduced pressure affords the desired flexibility. This results in a much higher degree of comfort to those who travel in the car, while depreciation rate an4 repair cost of both the chassis mechanism and the coachwork are reduced. The tyres are much more easily able to recover from shock. For instance, a wheel meeting a stone which is outstanding, if fitted with a low or medium pressure cover, does not tend to rise, and con- sequently to lift the frame through the spring so high as in the case of a high-pressure tyre, because the flexible cover allows the stone to depress the tyre while the hard cover will tend to go over it with the resultant upward kick. This means that the depth and- length of vibration will be reduced with the increased flexibility. The better the road-holding qualities of a vehicle the greater the tractive effort and the less the fuel consumption for a given distance. Meanwhile, tractive effort clearly affects the efficiency of braking or deceleration force at the disposal of a driver, more or less irrespectively of the effectiveness of his braking system. Again, it is evident that the less the front wheels of a car bounce, and the more they hold to the contour of the road, the greater the steering control.
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Another advantage is that with the additional area of contact between the tyre and the road obtained with the low-pressure or balloon tyre,. tendency towards sideslip.and to skid is reduced. I have already referred to the reduction of shock afforded to the chassis and bodywork and the lower cost of maintenance thereby, and it should not be overlooked that the more pliable tyre assists in _ greater proportion unsprung parti of the chassis compared with those which are sprung. Clearly we have not arrived at perfection in the motor car or in any one part of it, and tyres are no exception to the rule. The low-pressure tyre, by reason of its increased flexibility and area of contact, somewhat reduces a vehicle's speed in comparison with the hard tyre. This means the use of slightly more fuel for a given distance, while again an occasional extra change of gear may be called for: Such drawbacks, however, are more than offset by the advantages. Nevertheless there is one point to which attention must be milled, as it affects the life and therefore the cost of upkeep of the tyres very materially. The balloon tyre, to give the best results, must be kept at n constant Pressure, and this means that it calls for appreciably More Periodical inspection than did the high-pressure tyre. It should be remembered that a small drop in presiure in the low. PS CS/Ver is far more serious than in the high-pressure type. If, therefore, an owner wishes to get the most out of his cars he would be wise to test or have h,is chauffeur test the pressures once if not twice a week, when any necessary correction can be made. In my experience tyre manufacturers usually advocate pressures which are on the hard side. These will give the maximum tyre mileage but at the sacrifice of chassis and body depreciation and the comfort of the pas- sengers. It will do no harm, therefore, if the pressures are not quite up to makers' recommendations, and it is often advisable to keep the front tyres at a slightly lower figure than the back ones. The main points are that the respective pressures should be kept constant and that the pairs of wheels should be pre- served at the same pressure. Such points as not scraping the walls of the cover against a kerb or running over such an obstruction in order to save the trouble of a reverse, and picking out small stones and grit in the tread before they have a chance of working in deeply, apply equally in the matter of tyre economy to the balloon or low-pressure cover as they did to the older pattern of tyre.
Chassis lubrication is, next to the care of the tyres, one of the dullest occupations for the owner-driver and for that matter for the chauffeur. Because of this and its tiresome- ness in many cases it is often neglected. No machinery will run with prolonged reliability nor with satisfactorily econo- mical results without adequate lubrication, and by adequate I mean little and often rather than much infrequently. Little and often is the golden rule which ensures sweet running and durability. The gre_ase-cup has been discarded, and not before it was time. The nipple for use with a grease or oil gun is a distinct improvement, but when all is said and done it is a compromise, because, apart from the question of the operation being dirty, the system entails too much labour. The writer has for several years urged the adoption of automatic or half- automatic chassis lubrication, in which all parts throughout the chassis requiring oil can be fed automatically according to mileage or by the driver depressing by hand or foot a piston in a cylinder. The matter of cost has clearly been a difficulty from a manufacturer's point of view, because such a system is not as easy to devise, to work satisfactorily, as it may seem at first sight. For example, different types of bearing want different amounts of lubrication, while it is obviously essential that parts near the source of supply should not be overfed while those more distant are starved. A beginning, however, has been made, and I believe that this time-saving system of chassis lubrication will be almost as rapid in its adoption as was the low-pressure tyre. Already several makes, of different nationalities, such, for example, as the British Armstrong-Siddeley and the American Packard, are sold with half-automatic chassis lubrication as a standard fitting. It is a progressive move and one which will save the owner-driver much needless and tiresome work, and by making the chauffeur's duties lighter will conduce to a smaller expenditure on upkeep by the owner.
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As motoring becomes more general as a movement so does the amount of skill in driving decrease in proportion to the number of vehicles, and for this reason designers aim at simpler construction and control. One result of this is the provision on a considerable number of makes of car of recent date of a control which governs automatically or automatically within limits the advance and retard of the spark. This saves possible abuse resulting in needless petrol consumption or depreciation of the engine bearings, which will occur if the ordinary spark regulation is disregarded as a rule by the driver. If the lever is left up,or in advance position there will be times when the load is heavy on the engine and the charge in the cylinders is being fired too early. This involves back stress, which causes wear in the bearings and produces "knocking." On the other hand, if the engine is run with this part too much retarded full power will not be obtained, petrol consumption for a given distance will be unduly heavy, and the engine will run at an undesirably high temperature. Automatic control of the time at which the charge Is fired, according to the load and speed of the engine, is therefore an advantage, because it saves the driver some trouble, and the owner, where the car is not skilfully driven, expense. The device usually consists of some form of centrifugal governor which moves the- make-and-break. Where the arrangement is termed semi-automatic it generally means -that extreme retardation and extreme advance can be done by hand by means of the lever provided as a rule on the top of the steering wheel, while the intermediate range is worked automatically, One or two other features will be subsequently dealt with.
_ , YOUR MOTORING CORRESPONDENT.
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