TRICYCLE (from prefix tri, three, and Gr. circle, wheel). The tricycle, as a machine for pleasure riding, has steadily diminished in relative importance since the advent of the safety bicycle (see Cycling). In its modern form it is a chain-driven rear-driver. The driving axle is provided with a differential gear, which allows of both wheels being driven whether the tricycle is moving in a straight or in a curved path. There are four rows of balls, two near the middle resisting the pull of the driving chain and two near the road wheels supporting the vertical load. Two types of driving axle are in use. In one the axle is supported from a parallel frame tube by four short brackets. In the other type, the StarleyAbingdon axle, the frame tube is concentric with the axle, and the middle portion is enlarged to form a casing for the chainwheel, with two apertures for the chain to pass through. The other mechanical details are nearly all similar to those on a bicycle.
Carrier tricycles, for tradesmen's delivery purposes, are made in two types, one with an extended wheel base and the carrier behind the rider, the other with a single rear driving wheel, the two steering wheels and the carrier being mounted in front on a transverse tube or frame which is jointed to the rear frame at the steering head. The second arrangement gives the simplest possible form of tricycle, but it is unsuited for touring purposes.
The tricar or motor tricycle was first made by removing the front wheel of a motor bicycle and replacing it by a frame carrying two side steering wheels and a seat. With a powerful engine this arrangement gives a light vehicle from which good performances are obtained on roads with easy gradients. On steeper gradients the power must be increased, and the belt drive with only one speed is inadequate. The modern tricar is on different lines, resembling a small motor car on three wheels. The engine is 6 to io h.p., preferably with two cylinders, air or water cooled, with clutch and gearbox giving two or three speeds, sometimes also a "reverse" speed. The transmission is usually by a chain from the engine shaft to the gear-box, thence by another chain to the rear road wheel. The frame or chassis is supported on the three road wheels by springs. The steering gear is on the same general lines as that of a motor car. The weight of a tricar of 7 to 10 h.p. is between 700 and 1000 lb. It is a much faster vehicle, especially uphill, than a small car of equal price. The rear tire, however, is subject to severer working conditions than the two driving wheel tires of a small car, and must be of adequate strength, or trouble will be frequent.
The tricar cannot be said to have attained to the same degree of trustworthiness and freedom from breakdown as the motor bicycle or motor car. The rear tire is difficult to remove, in case of puncture. The chain drive, direct from a small chain-wheel on the engine shaft, is faulty in principle. The engine shaft running often at 2000 revolutions per minute, the chain is necessarily noisy, and is subject to continual gradual stretching, necessitating frequent readjustment. In all respects, except speed, the tricar is inferior to the small car. (A. SP.)
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