VEHICLE, HARNESS, AND SADDLE 



289 



snug to the shoulder instead of running off as it would tend 

 to do with an unpitched tapered axle (Fig. 158). Incidentally, 

 this pitch places the tops of the wheels farther apart and, there- 

 fore, throws the mud or dust away from instead of against the 

 body of the wagon. 



Wheels are dished, that is the spokes are set in the hub at an 

 angle, instead of perpendicularly, for several reasons (Fig. 

 1.59). In the case of a pitched axle, dish- 

 ing brings the spokes of tiie lower half of 

 the wheel into an upright position, in 

 which they are capable of sustaining the 

 greatest weight. Dishing also braces the 

 wheel against being sprung by a lateral 

 thrust from the inside, as occurs when the 

 vehicle bounds back and forth from side 

 to side over the road. Dishing also 

 affords an automatic means of keeping 

 wheels tight. The effect of wear and con- 

 tinued battering over stones, rails, and 

 all kinds of rough roads is to expand 

 metal tires, thus allowing the spokes to 

 loosen in both hub and felloe. In the 

 dished wheel, however, the spokes are not 

 only set at an angle, but the tire, after 

 being expanded by fire, is fitted so close 

 that when suddenly contracted by cold 

 water it draws the ends of the spokes 

 into a still greater dished position than 

 they were originally set in. Therefore, 

 any expansion that occurs in the tires 

 is immediately taken up by the spokes 



springing toward the perpendicular. The centrifugal force of 

 the revolving wheel also operates to throw the spokes into a per- 

 pendicular position, which assists in keeping them taut against 

 the felloe and tire, by which they are bound. 



In pitching the axle arms or dishing the wheels, care must be 

 taJjen to keep the tire parallel with the road surface so as not ti > 

 drag or scuff, as motorists say, but roll evenly over its entire width. 

 19 



Fig. 159. — The dished 

 arrangement of the apokes in 

 the hub. 



