How To Drive A Motorcar
A Key To The Subtleties Of Motoring

CONTROL OF THROTTLE in the chassis. It is very bad for the mechanism of the car suddenly to call into play the full available power of the engine, and it is certainly the reverse of economical. If the reader were to fix a graduated glass tube about a couple of feet in height on the dashboard, the markings being, say, in cubic centimetres, it would probably be something of an eye-opener to him to see the disproportion between the quantity of petrol used in sudden acceleration and the actual benefit accruing from it. Even beyond this many carburetters do not give the best actual acceleration by the quick and full depression of the pedal, but give better results by a fairly fast depression of the accelerator pedal at a con- stant speed in the early part of the movement, gradually speeding up the depression from about the one-third open position. One may lay down another good honest rule with regard to the control of the throttle to the effect that one should never make a habit of driving for long periods with the throttle fully open. It is bad all round—it is wasteful—very wasteful—it is bad for the mechanism of the car, and it is unmechanical. On the contrary, one should do 80 or 90 per cent, of ordinary touring on approximately level roads with a good reserve of throttle movement in hand. If, again, the reader could take advantage of the diminutive glass petrol tank previously referred to, the difference in economy when running with the throttle full open and, say, from about half open to two-thirds of full depres- sion, would be a considerable surprise. Presume for the sake of argument that the maximum speed of the car assumed to be under consideration is 45 miles per hour. For such a machine the ordinary fast touring speed should not be more than from 33 to 37 miles per hour. Every car has some definite throttle opening at which it will “ get along very well,” and it may be that only, perhaps, six or seven miles per hour faster can be obtained with the maximum throttle opening. Yet the difference in economy so far as petrol con- sumption is concerned between the unkind driving and 77