Motor Road Transport For Commercial Purposes
(Liquid Fuel, Steam, Electricity)

SELECTION OF VEHICLE 31 times, but there should be, in addition, a reserve of power. There is no surer way except by constant over- loading, which has the same result, of making a delivery service a failure, than by the employment of vans which are under-powered for the transportation of the maximum load for which they are designed by the makers. Power, Speed and Gear Ratio. It is necessary to emphasize the faet that as power and speed in all forms of engineering are inversely proportional, the range of gear ratios provided on a chassis affeets the question of power supply to a large extent. Broadly speaking, the greater number of gear ratios there are the better, since the wider variation afforded between engine and vehicle speeds enables the motor to be run more efficiently. The reason for this is that as far as the internal combustion engine is concemed it will, as a rule, give off its highest power within a certain small range of piston speeds. This range lies well above the minimum number of revolu- tions per minute at which. the engine will run and pull, and is yet below the maximum at which it is possible to race it when running light. It will be clear then that the ideal condition would be that under which the driver, when ascending a hill, could keep the engine running at the maximum of efficiency by frequent changes of gear as the load on the engine tended to reduce its speed. This condition is, however, not realizable where gear wheels are employed, since the construction of such a gear box would be impracticable owing to cost, weight, and size. The above will, nevertheless, instance the advantage of a four-speed box over one fitted with only three, and the three- speed model over the two-speed pattern. This is