All applied mechanical power is the application of lever movement (and lever movement is but the effect of applied power), either simple, compound, or complex.

In the bicycle propelled by human power, we have a series of lever movements, initiated and executed by the highest and most effective mechanism known—the human body, applied human power. There is the seat of power, the point of application, and the object. The bicycle or object is so constructed that it continues the application of power applied.

The lever is described as “a bar or other rigid instrument having a fixed point for the exercise of power and the application of power to the object to be moved.” The series of lever movements in the human body is the most wonderful known.

There are three varieties of levers, of three different degrees of efficiency, known as levers of the first, second, and third classes, or orders, of levers.

In the lever of the first class, the fulcrum is between the weight and the power:PFW.

In the lever of the second class the fulcrum is opposite to the power: PW F.

In the lever of the third class the fulcrum is opposite to the weight: PW F.

These different powers of levers are used in combination, and produce a great variety of power effects and applications.

Other factors to note are:

That a body in motion persists in maintaining its direction unless other forces intervene.

That the gyroscope overcomes the force of gravity while rapidly revolving.

That a body set in motion tends to move in a straight line.

That the centre of gravity must be maintained by balance if disturbed or shifted.

That force is the cause of a change in the velocity or direction of motion of a body.

That all alterations of velocity take place gradually and continuously.

That centripetal force and centrifugal force are force directed by radial action.

That the air offers resistance, which increases when the air is in motion.

That friction offers resistance to power.

That the smaller the surface presented, the less friction there is to resist.

That resistance must be overcome by power expended for the purpose.

That the base of the bicycle is practically without width, and is usually about from forty-two to forty-four inches long.

That the direction of the base may be changed at will within certain limits.

That the bicycle will fall unless prevented from doing so.

That to prevent a bicycle from falling, or to maintain a bicycle on its base, it is necessary to balance it.

That the constant effort to maintain the bicycle upright upon its base is on account of the motion of the different opposing forces.

The bicycle is constructed to overcome the resisting forces in different ways, supplying as many forces as can be made available to accomplish a particular purpose, permitting a certain choice and discrimination in the matter.

The bicycle has one weight-carrying wheel and a frame and a pivoted wheel. The driving power is applied to the weight-carrying wheel, and the steering is done with the pivoted wheel. The bicycle remains upright because several forces co-operate to enable it to maintain its plane, change direction, and overcome certain resisting and opposing forces.

A bicyclist is propelled at a sufficient velocity to maintain the plane of movement. By altering the centre of gravity, inclining one way or the other, change of direction may be made.

The front or guiding wheel of the bicycle, being controlled by the different angles of resistance it presents to the surface it rotates upon, and not being immovably fixed, can pivot to a plane corresponding to a plane of least resistance. After a little momentum is attained, a bicycle will maintain its speed with but little assistance of power, unless it is accidentally obstructed, or an increase of grade requires an increase of power.

The frame of a bicycle is a compound lever, combining the second and third orders. The wheels are a compound lever of the second and third orders. The fork and handles a lever of the second order.

The forks and handle-bars are set at an angle with the front wheel, thus conveying the touch on the ground or other surface to the pivot head and the hands.

A moving body tends to pursue its direction. A wheel loses its power to change its direction after passing the point of friction. With the forks at this angle, the blow is felt, and change of direction caused by an obstacle conveyed; but the wheel has still some power to maintain its plane from friction, and is steadied by its head. The motion of swaying is conveyed and overcome at the tire base. If the pivot were directly over the tire base, the swing would be given to the wheel; and the tire, having passed its point of friction, would continue to swing. If the head were pivoted on a point, there would be no side friction on the rim; because it is pivoted at an incline, the friction base is increased in proportion, and the wheel, steadied in itself, is easily controlled by an increased line of friction or by prolonging the time from the point of contact.

A body in motion persists in maintaining its plane of motion unless additional forces intervene. The occurrence of these forces is detrimental and frequent, requiring a continuous swing of the guiding wheel either by the hands or by balance. The direction of the base line is continually changed, as it were, broadening the base line. The weight must incline with the front wheel, and the front wheel will support it. If inclined away from the direction of the front wheel, the weight becomes the long arm of the lever, exerting weight against weight at the base of the bicycle, there being no opposing force. The front wheel being turned away, the bicycle falls or slips over.

With the fork at this angle the wheel is inclined, the frame held on the wheel at this angle, as the wheel is turned sideways, it gradually brings the centre directly over the axles, raising the front end of the frame up. This pressure or leverage from the frame tends to keep the wheel straight in the line of least resistance. In turning, the wheel must lift the weight, and push it up; and this factor greatly adds to the steadiness of direction.

A bicycle with the steering wheel held fast will maintain its plane so long as its momentum is not overcome. With the steering wheel the plane of movement may be regained after each opposition, provided the proportionate amount of power is expended.

The radius of a wheel is the long arm of a lever; the pedal crank is the short arm of the lever, though its length may exceed that of the radius of the wheel.

Power and speed are interchangeable. The shorter the arm of the crank, the greater the weight required to balance the long arm at the rim of the wheel (an imaginary line). If the pedal crank is lengthened, it will require less power to move it. At the same time the foot, following the crank, describes a larger circle for the distance travelled by the rear wheel. The crank lengthened, the power is diminished, demanding increased exertion to follow it, the foot travelling at a rate determined by the distance to be traversed.

When the hub rests on the axle of the wheel, there is considerable friction to overcome in the entire length of the hub, the friction, or ability of the wheel to turn, depending on the amount of axle surface. The axle, therefore, becomes heated when the air cannot readily reach the surface to convey away the heat generated by friction.

Weight may be balanced and supported on a point; when weight rests on a sphere, only a point supports weight. By surrounding the axle with balls, the weight is taken from point to point on each ball, and a circulation of air allowed. The weight, carried from ball to ball, gives the advantage of a larger cooling surface in a confined space, while the weight and friction are applied directly to a very limited area. Each ball is also an axle in itself, and carries the weight, and passes it on to the next ball. The balls act as lubricators, preventing the moving surfaces from contact.

The problem of speed produced by power means that speed is obtained at the expense of power expended. The relative size of the sprocket-wheels determines the relative speed of the cranks and rear wheel. To get the greatest speed with the least power possible means diminished friction and lessened weight. The band or chain complies mechanically with these requirements, permitting a certain amount of play, which lessens the danger of sudden strains and jars, and supplies the power to the rear wheel with the least possible loss by friction.

“Scientific American Supplement, No. 1025,” August 24, 1895.

Rating wheel by the amount of progression for each turn of the crank (pedal), the following table, compiled by Henry Starkweather, will be found of advantage:

The following table, from the New York Evening Post, shows the gear according to the number of teeth on large and small sprocket-wheels: