MODERN MOTORING

Auckland Star, Volume LI, Issue 142, 15 June 1920, Page 8

MODERN MOTORING

(BY TORQUE.)

HORSE POWER. ilany persona who are contemplating buying oars are often puzzled at the fact that a car in America ib sold as a 45 horee power while in England it is rated as about 25 horse power. To thoroughly understand the question it m really necessary to revert bark to the days of Watt—the inventor of the Pteam engine. The first application of early engines was for pumping water out of the mines in Cornwall, the work then being done by horses. Watte experiments showed that a good horse could average 22,000 "foot-lbs"' per minute of work for a day's average work. A "foot-lb" is equal to a weight of lib lifted 1 foot high,- and 22,001) foot-lbs may be. I,ooolb lifted tl feet or any other equivalent -amount. In order to make a good impression with Ms steam engines he decided to increase his rating by 50 per cent, in otiicr words he established 33,000 foot-lbs as one horse power, so that in practice one of his 2 horse power engines was really equal to 3 horses. Thue it comes about that the recognised horse power of toj day is an engine capable of delivering ' energy corresponding to 33,000 foot-lhs per minute. Then when petrol engines first came on the market, they were usually tested by means of a "brake,"' that is a power-absorbing device that readily gives the power available from the engine shaft, hence the term ""brake horse power." Then designers of petrol engines sought for a formula co that the average horse power could be calculated from the bore of cylinders which would be a fairly accurate indication of the hor~e power developed in tho*e days, and give a 'buyer a good idea ol what an engine ought to do. Thus we have the R.A.t'. formula of England, where the hora(% power equaU the diameter of cylinder in inches squared, multiplied by number of cylinders and divided by 2.5. From this formula ',t Will be noted that the stroke is ignored, and it ie assumed that the piston speed, is 1000 feet per minute. Thus it will be seen that the formula is far from accurate nowadays, but is still in use in England for purposes of taxing cars by horse power basic. Enormous improvements have been made ,n the design of internal combustion engines, and at the present day it is no uncommon thing for an| engine when tested to develop at least three times the power assumed by the R.A.'C. rating. The Hudson engine ie rated at 20.4 'R.A.C. horse power, but will develop a'boi>t 91) bralke horse power. The 15 h.p. "Wolseley will do nearly 46 b.h.p., and the 10 h.p. Humber will touch nearly 30 : b.h.p in practice. One of the engines to be used in the coming races in 'U.S.A., although rated by R.A.C. method at only 2O h.p., has been tested in the shops to 108 brake horse power! It ie impossible to calculate the horse power of any internal combustion engine from any one formula, and the method ruling- in England for taxation has forced the adoption of sroall bore, long stroke engines, which have been developed to a high degree of perfection. Most of the American manufacturers now rate their engines also on the"S.AJE. fating fSocie"ty of Automobile Engineers), the formula being the same as ruling in England, but aleo give in the car specifications the actual 'brake horse power developed at a stated maximum number of revoluitions per minute. And some of the makers aleo list a "nominal" horse power. For instance, an engine may be 25 Ji.p. by S.A.K. rating, and actually develop 90 brake horse power at, cay, 2990 revolutions per minute. The sales department would call the engine, cay, "70 horse power," this amount being an assumed horse power that the customer ought to readily get out of the engine under average conditions on the road. The R.'A.C. formula really only gives a 'buyer an idea .of size, as it were, but the b.h.p. at a etated number of revolutions is the best guide of an engine's ability. PNEUMATIC TRUCK TYRES. It is doubtful if any one topic has teen more freely discussed I>y prospective truck buyers than the question pneumatic versus solid tyres. Pneumatic tyres were being used on trucks as far back as 1908, on 2 and 3-ton models, but it was not until 1915 that real progress was made by superior tyre construction suitable for the work. The fitting of pneumatics to all sizes up to and including 3 A-ton models, is one of the greatest movements taking place to-day among the U.S.A. manufacturers. The growth of the pneumatic tyre on trucks has been a nay in advance of the expectations of the most optimistic. Some of the leading tyre manufacturers, building giant pneumatics for trucks, have not been able to keep abreast with the demand. Although the movement started but a few years, ago, approximate!}' 135,000 motor trucks fitted with pneumatics will "be delivered by manufacturers this year. This out of a total expected production of 325,000 trucks for this year is indicative, not only of the demand, but of the appreciation of this demand by the truck maker. Approximately 50 per cent of all motor trucks built in 19:21 will be fitted with pneumatic tyres as factory equipment in TJ.S.'A. The increased speed of a motor truok on pneumatics is the most fascinating phase of this new movement. This added speed brings forward one of the most serious problems in connection with it. When <v truck speed is jumped from 14 miles per hour to a possible 20 or 24, many things happen. Generally the engines will not stand up for this higher speed. Their lubricating system may not prove adequate. Their bearings may not be sufficient. There is literally a dozen respects in which the engine designed to operate at 1000 r.p.m. or 1200 r.p.m. for solid tyres cannot withstand the harder service of 1600 r.p.m. or perhaps more that might be needed on pneumatics. In actual practice some engines where the epeed has l>een very higih have been broken down in 500 miles. • This is no reflection on the engine but the natural outcome of endeavouring to operate it at much higher crankshaft speed than it was designed for. This higher pneumatic tyre epeed is too frequently misunderstood. Too many imagine that the great advantage of the pneumatic tyre comes from an average of 20 m.pJi. or perhaps higher, In general service the greater mileage of the pneumatic tyred truck is due to bringing up the low average. A eolid tyred truck will have to slow down to 4 m.p.h., on rough going, whereas the same truck with pneumatics might pas« over such a road at V 2 or perhaps 15 m.p.h. It is hy increasing the average of the slow epeeds that the pneumatic tyred job makes its showing rather than by jumping the top speed from 14 to 20 or 22 m.p.h. Because of this the extra

be imagined. Bringing , up the low average, speeds as indicated does not carry the engine speed unduly beyond that of eolide. Some figures from tyre companies are quoted here for the purpose of rounding out the picture of the pneumatic tyre. Two trucks of two-ton capacity, one -operating on solid tyres and the other on pneumatics, in a mileage of 3850 each, the cost for benzine on the solid t>' re )<ft> was £47 10/, and on the pneumatic tyre job £33. Jn another comparison of two trucks two-ton capacity each, one with solids and the other pneumatic, the cost per mile was 1/7J on pneumatics and 3/3 i on solids. This wae ;based on 1000 miles of use and includes all rosts, such as depreciation, overhead, c-tc. TJie greatest economy, at least it is considered so. is that which comes from reduced vibration, which is equivalent to reduced maintenance of the truck. Where vibration is reduced from 15 per cent, to perhaps 40 or 50 per cent, in many cases, the reduced upkeep of parts can best be appreciated by those n<lo have had experience with maintenance handling. IT IS RUMOURED— That a council tlog inspector is now a liojf inspector—-road uog's of course! That a man with a red flag and. a whistle directed traffic at Newmarket on race da ye. Qu'He American! That another benzine shortage was coming if the tram strike hadn't ceased. That although a jockey was not allowed to go to Crisborne by boat —he got there all right by car. That <Jueen Street will have to be widened for some drivers. That an unannounced police inspection of brakes would bo valuable evidence of the cause f accidents. That come of the safety zone signs are really dangerous to strangers when turned at right angle? and unlighted at night. That the car services to Waiuku have been discontinued. Roads won the contrst. That the cost of livinsr is coming down. Threepence for a tram instead of one shilling for a bus! That there are over 170 tj"re companies making tyres in U.S.A.