THE MECHANISM OF BICYCLES. 
387 
and C is a constant depending upon the nature of the road and the 
form of tire both as regards its resilience and its air pressure, and it 
is stated that experiments show C to have been reduced by pneumatic 
tires to one-half what it was with non-elastic tires. The value of C 
may be roughly taken as follows : 
On asphalt or wood.... 
.. C = 
•06 
Good road. 
... C = 
•2 
Fair road. 
... c = 
•4 
Poor road. 
.. G = 
1-2 
The second resistance R 2 is that offered by the air and the formula 
used at the Greenwich Observatory may be taken as a guide. 
It is R s = *003 V 2 A. 
where A is the mean plane surface offered to the air, but in the 
case of such a complex body as a bicycle and rider and owing to the 
action of the spokes in cutting through the air, it is believed that 
A requires to be multiplied by some co-efficient less than unity. V 
represents the sum of the velocities in miles per hour of the machiue 
and of the wind if riding against the wind and the difference of 
the two if riding with the wind. 
It may be mentioned that a high wind blows from thirty to thirty- 
five miles an hour, a storm fifty miles and a hurricane eighty miles. 
Although not recommended for ordinary riding, it is easily seen 
why the ‘ scorcher 9 and racer bend over the handles, for by so doing 
they diminish the factor A to a considerable extent. We also obtain 
an explanation of the fact that has no doubt been apparent to many 
riders that the faster one goes down a hill (with the feet on the 
pedals) the more power one has in back pedalling. 
I do not think it would serve any purpose to give a formula for R z , 
the resistance due to the friction of the ball bearings, chain and 
sprocket wheels, but I have the results of two entirely independent 
series of experiments before me. One series carried out by Professor 
Goodman, of the Yorkshire College, Leeds, from which he finds that 
about 2 °/ Q is lost by R 3 , thus making the co-efficient of efficiency 98. 
(This is, of course, for a well made machine in good condition and 
properly lubricated). 
The other series was carried out by Professor Carpenter, of the 
Cornell University, and from the results it is seen that the highest 
efficiency obtained in the case of a chain-geared machine was 97°/ 0 , 
the friction of the chain itself being shown to vary from *8 °/ 0 to 
2*5 °/ 0 . Professor Carpenter also found that the friction of the chain 
was independent of the speed. The efficiency of chainless bicycles 
was somewhat less, but in their case the co-efficient of friction 
decreased as the speed increased, so that the effort of propelling a 
geared machine at low speeds, as in hill climbing, was relatively greater 
than that of propelling a chain machine. He also found that the 
total friction increases but the co-efficient of friction decreases with 
an increase of load for both kinds of machine. 
