CH. Ill SIZE OF WHEEL 47 



to the front ; this is called the ' o-ather' of the axles. 

 A light axle will spring backward when the draught 

 upon it is opposed by the resistance of the wheel 

 on the ground ; the axle-arms will be no longer in a 

 straight line, and the wheels will not be parallel to 

 each other or to the centre line of the carriage, 

 hence they will run against the nuts instead of 

 against the collars ; and if the axle-arm be tapered, 

 the motion of the carriage causes a pressure against 

 the front side of the taper, and increases this ten- 

 dency, so that, to counteract it, the gather must be 

 still more increased. 



Wheels, when not parallel, will rub sideways upon 

 the road and increase the resistance. When an 

 old carriage has axles badly bent, the wheels may 

 be observed to plough up the mud on the inside of 

 their rims as they move along. Cabs in a crowded 

 city, which frequently have collisions, sometimes 

 have their axles bent back in this way, and it will 

 be seen that their tires are polished from being par- 

 tially dragged on the surface of the road instead 

 of running with a true rollino- motion. In coaches 

 which have very strong axles and parallel arms, the 

 necessity for gather does not exist, and it is not 

 given ; but in overhauling a coach, or in buying one 

 second-hand, it is important to notice whether or 

 not the axles are in the least decree bent backward. 



The height of coach wheels varies, in the best 

 examples, from 4 ft. 2 in. to 4 ft. 4 in. for the hind 

 wheels, and from 3 ft. 2 in. to 3 ft. 4 in. for the front 



