the biggest radius or curve must travel further than the inner, which remains practically stationary or turns very slowly, according to the sharpness of the curve.
Starley overcame this by fitting a balance gear which enabled one wheel to over-run the other when the tricycle was deflected from a straight course, and yet allowed both wheels to take their equal share of the driving power. Previously, only one wheel was driven—the other running loose on the axle.
Whether Starley actually invented the device or adapted it from Aveling and Porter’s road traction engine is obscure; in any case he should have the credit of being the first to recognize its importance. It may be added at this point that practically every motor car is provided with a balance geared axle.
The designs of tricycles went through several stages. There were rear driven tricycles with one wheel at the rear and two front steering wheels, double driving tricycles with two rear wheels and one front steering wheel, both having three tracks. The advocates of two tracks made machines with two rear driving wheels and the front steering wheel in a line with one side driving wheel (usually the off side)—the Royal Mail was one of this type. Then came a most ingenious machine, the Rudge Rotary. Haynes and Jeffries, who preceded D. Rudge and the Rudge Co., had made a machine on these lines, but when the storage of a tricycle was tackled by the makers it was found that to enable a tricycle to be wheeled through narrow doorways it must not exceed about 2 ft. in width. The ordinary tricycle was about 3 ft. wide.
The ingenious Rotary was made with one large driving wheel, so dispensing with the differential or balance geared axle. The rider sat on a saddle perched over a frame that extended fore and aft with its centre about