Speed and Acceleration

Sun (Auckland), Volume II, Issue 420, 31 July 1928, Page 6

Speed and Acceleration

How They Affect Each Other

A SIMPLE DESCRIPTION

SIXTY miles an hour on a stock and model touring car was, until a few years ago, only possible under road conditions by machines expressly designed as “sports type.” Which makes one believe that motorists and fishermen have much in common—the former in respect to Speed, and the latter as to weight or size of catch.

Yet although many drivers will stoutly testify as to even-time Speeds in years gone by, an analysis of the flying mile records of the Royal Automobile Club of Australia is good and sufficient evidence to the contrary. Here were cars, well tuned for competition work, and in the hands of clever and experienced drivers. But, until 1924, out of 250 cars tested, only 17 had clocked better than 60 seconds, and with one or two exceptions all were of the sporting type. To-day, however, we find, a host of stock models—family cars, in fact—capable of a genuine “60” when fully loaded; and I have been asked on a number of occasions whether this general increase of maximum speed is detrimental to “pick up” or acceleration of that particular car. Before going into the pros and cons of the relation between acceleration and top speed, it must' be understood that power units of to-day show such remarkable improvement both in flexibility and in horse-power output per cubic centimetre that this fact must be given due notice when some of the phenomenal results are under consideration. In spite of this, acceleration has just as important a bearing unon the maximum speed of any car as it ever had. A TEST For instance, let us choose a machine with a maximum speed of, say, 70 m.p.h. and a back axle gear ratio of four to one. After selecting a suitable road and making 'sure no police are in sight or hearing, we start to speed tip in top gear, beginning with

the speedometer registering 10 miles an hour. Ten to 30 m.p.h. will be a slow process of “winding up,” and it will not be until the dial is showing somewhere around 45 that the engine seems to get hold of its work and shoot the car along. Now let us change our back axle gearing to four and one-half to one, and do the same tests. A very great improvement will be noticed, and acceleration will be smarter. But the maximum speed will have fallen to perhaps 66 m.p.h. Change again to a five to one gear, and still better acceleration will be obtained. Bat this time the best allout speed will be about 63 to 65 m.p.h. Clashing Objectives Obviously, in producing a new model, designers are faced with a difficult problem when considering top gear speed and acceleration. It is one of those situations where they would like to have their cake and eat it as well. For buyere clamour for a car that will accelerate smartly in traffic from a crawling pace, and at the same time are peeved if the maximum speed is not in the neighbourhood of 60. The simplest solution would appear to equip the car with a large motor and fit a very low back axle ratio. But this method can easily be overdone, for fastidious owners will not stand an* engine fussing under the bonnet at high revs, when touring at normal speed. On the other hand, the racing car or special sports type will supply all the speed any reasonable person desires, but acceleration from 10 to 40 miles an hour is painful, and can be beaten by almost any cheap quantity production touring model. Steam Cars Supreme Steam cars are famous for their powers of acceleration and top-gear speed. No internal combustion motor-car approaches them in this respect, and therein lies the crux of the whole situation. Until a petrol engine is designed to give something like constant power at all speeds, speed and acceleration must be in the nature of a compromise. Actually much progress has been made of late years in this direction, and the graph, showing power curves of sports type and tourer, is interesting for purposes of comparison. This graph tells its own tale and shows at a glance the reason why the family ca.r of to-day “picks up” better in top gear from low speeds than does the sports type. Sports and Tourer At low engine revs, the tourer gives off much more power than the corresponding sports type, and this means when the cars are slowed down under road conditions the tourer will get away very smartly; while, unless a change of gear is made in the “sports” it will be a process of winding up. My first practical illustration in this matter came rather as a shock. Cruising along at the wheel of an 80 m.p.h. sports car, a friend pulled alongside in a medium-priced sedan. The speed of both cars was then about 20 m.p.h., and my friend challenged me to an acceleration test from that speed over a distance of 50 yards. Much to my surprise and chagrin, I was beaten by quito three lengths! Where the Motor-Cycle Wins Of course every driver of a car knows the futility of “dusting up” with

a motor cyclist. For the latter can, from an acceleration point of view, leave the four-wheeler standing wherever he choses. This is due, however, to the power to weight factor. A welltuned motor-cycle has available one horsepower for every 101 b weight of machine'and ride.i* while for the average car the figure is nearer one to 40. Obviously, if the car designer were to equip his machine with such a ratio of engine to weight, the fuel bill and running costs would be out of reach of most people.

TRAMS REDUCE TRAFFIC NEW YORK INVESTIGATES Looking forward to double its 9,000,000 population by 1965, New York is preparing to set its traffic system in order. A special committee has spent five years in investigation, and has now issued a regional plan. Main suggestions of the committee are: The construction of several belt lines of highways running in concentric circles around the metropolitan area; a series of radial highways diverging toward these; double-deck streets; more bridges over the Hudson River; car tunnels under the East River, and even across Manhattan Island; elimination of trams on main streets and substitution of buses; reduction of taxis; widening of streets; limitation of building heights in congested areas; and raising of railway crossings. If all these were adopted, it is said, the city and suburbs within a radius of 50 miles could easily accommodate 20,000,000 people. Ferries and lack of bridges have been the chief causes of congestion, while trams, it has been found, reduce the traffic capacity of the streets by from 20 to more than 25 per cent. Taxis, too, are said to hold up traffic, for a single bus can take care of as many passengers as 40 taxis. Though the buses numbered only 12 per cent, of vehicles on the busiest streets, they carried 64 per cent, of the passengers.