RUNNING COSTS

Evening Star, Issue 22413, 10 August 1936, Page 15

RUNNING COSTS

THE FACTOR OF SPEED Everyone knows that the cost of running a car increases as its speed rises. But how much? To answer this question ‘ Motor ’ (America) asked the various XJ.S.A. car manufacturers, petrol, oil, and tyre companies for whatever information on the subject they had available. Averaging all the data, it was found that it cost 2 cents a mile more to operate a car of moderate size at 70 miles an hour than at 40. Below 40 miles an hour the effect of speed on cost was not great. To quote a typical case from a complete set of figures supplied by one of the well-known car manufacturing companies, if it requires about 6 cents per mile to drive an average American car at speeds of 20 to 40 miles an hour, the increased cost of running it at speeds of 60, 70, 80, and 90 miles an hour is respectively 1,2, 4, and 7 cents per mile in round figures, the actual cost per mile for these speeds being 7.34, 8.17, 9.82, and 13.36-cents. la arriving at these figures, it was assumed that the car be 4 i OOO mile* is two,, years, fixed‘‘costs ' being set down at average figures. Various costs, increasing with speed, were con-

sidered to be petrol, oil, tyres, and repairs, including brakes. Petrol consumption at 30 m.p.h. was taken at 17 m.p.g., with fuel costing 17 cents per gallon. (The gallon mentioned is the American gallon, not the imperial gallon.) Tyre life at 40 m.p.h. was assumed to be 24,000 miles, and the cost of a tyre and tube 21.80d01.

At 20 m.p.h. tyre cost was only .18 of a cent per mile, at GO m.p.h. it was .8 of a cent, while at 90 m.p.h. it soared to 3.27 cents. Oil is not a large item of expense, of course, but it is interesting to note that 16 times as much must be bought for continuous running at 90 m.p.h. as at 40. The cost of repairs is given at .3 of a cent at 40 m.p.h., and 1.3 cents at top speed. Other things being equal, brake lining wear is proportional to the square of the speed, which means that if a car were stopped always from 60 m.p.h. the lining would wear four times as fast as it would if brought to rest the same number of times from 30 m.p.h. * Rapid acceleration runs up the fuel bills. Figures submitted by a leading car maker showed that whereas during continuous running at 40 m.p.h. his car has » running economy of 17.1 m.p.g.. petrol consumption is at the rate of 9 m.p.g. when the car is accelerated on wide-open throttle in high gear. The rate is 4.5 m.p.g. in second, and only 2 m.p.g. in low. One car maker sums up the relationship between speed and fuel consumption by stating that fuel economy is reduced 15 to 20 per cent, when the speed is 40 miles an hour instead of 20, and is reduced 30 to 35 per cent, at 60 as compared to 20. The same manufacturer states that oil economy is reduced 10 per cent, in the first case and 50 to 60 per cent, in the second. Averaging the fuel economies in three makes of oars equipped with overdrive, there is a gain of 3.4 m.p.g. in overdrive as compared with direct drive —the figures being respectively 17.9 and 14.5 m.p.g.