42 COXED WHEEL CH. Ill 



carriage are sections of cones they will not tend 

 to roll straight on in the direction in which the car- 

 riage is going, but to turn off to the outside, as 



shown by the dotted 

 curves of Fig. 23 ; 

 consequently, they 

 ',:> will run against the 

 nuts, or linchpins, and 

 thereby set up a re- 

 sistance which will in- 

 crease the draught. 

 '///////////)?, i n addition to this, 

 the face of the wheel 

 having different diameters, its parts will revolve with 

 different velocities ; and as all parts must move 

 over the surface of the road at the same forward 

 velocity, there will be but one line of the tire that 

 will roll, all other lines of the tire being dragged 

 on the surface, with a grinding action that destroys 

 the road and the tire, and increases the draught. 

 Some old English wagons are said to have had tires 

 10 inches wide, and with coned wheels these would 

 grind on the road excessively. It was because, in 

 the last century, all wheels in heavy vehicles were 

 considerably coned, that the road authorities ob- 

 jected to wide tires as injuring the road ; wide 

 tires on cylindrical wheels are an advantage to a 

 road. 



In the figures an exaggerated amount of coning 

 is shown, for clearness, but exactly the same kind 



