THE MECHANISM OF BICYCLES. 389 
The velocity was 13 miles an hour and the work was measured by a 
pedal of special construction containing two dynanometers so as to 
register the power exerted in two directions at right angles to each 
other. The tangential and radial pressures are shown by the dotted 
lines, the former, however, are the only ones that are transmitted to 
the driving wheel, the latter being merely uselessly expended on 
the crank shaft bearing. The lines a b represent the position of the 
pedals and c d the resultant pressures. 
The diagram is very useful in illustrating the magnitude of the 
tangential pressures at 14 different points on the pedal path. It will 
be noticed there is a back pedal pressure from the position 9 to 13. 
This, however, must not be looked upon altogether as lost work, as a 
large portion of it is expended in raising the foot, work that would 
otherwise have to be done by the rider drawing the foot up. Work 
very fatiguing as will be readily remembered by those ladies and 
gentlemen who have had a turn on a treadmill. Where it appears to 
me that the diagram does not faithfully illustrate the action of 
pedalling of an ordinary road rider, is that it apparently represents the 
heel considerably raised at the top position, and therefore without any 
tangential component at that point, whereas most riders (with rat-trap 
pedals) will, I think, agree in saying that by sinking the heel a con¬ 
siderable tangential component can be obtained to help in getting the 
pedal over the top dead points of the crank circle just as a clawing 
movement aids in passing over the lower dead points, but it must be 
remembered that most probably the tests were carried out on a racing 
machine in a racing attitude, i.e., bending over the handles, the 
saddle well forward, as the tangential components at the lower portion 
of the circle (7 to 8) indicate. 
The most effective pedal pressure when encountering a hill or wind 
resistance is obtained by making the tangential pressures as even as 
possible. 
A word will suffice to explain how the invention of the pneumatic 
tire has revolutionized almost everything in the bicycle world. With 
a solid tire each obstacle met with not only brought a severe blow 
upon one particular spot on the machine, but the machine and the 
rider had to be lifted over the obstacle, entailing in the coarse of an 
afternoon's ride a vast expenditure of work. A pneumatic tire on 
meeting an obstacle yields to the pressure, the shock due to the blow 
is distributed over the whole wheel through the compressed air, while 
the machine and rider are not appreciably raised. A wider surface of 
contact is also obtained, the tire flattens instead of sinking into soft 
ground. This lessening of the shock has done more than anything 
else in reducing the weight of machines. From the results recorded 
on the racing path it appears that even on a smooth track the 
elasticity of the tire adds very considerably to the speed attained. 
The question of excessive knee action is one that often is discussed 
by bicycle riders, and it is a point which, I imagine, concerns ladies 
perhaps more than men. It is aflected chiefly by the position of the 
36 
