250 FARM MACHINERY 



bearings would tend to reduce the axle friction and man- 

 ufacturers trying to introduce these bearings claim a 

 great reduction in draft. No doubt there are other ad- 

 vantages in the use of ball and roller bearings beside a 

 reduction in draft. It is not thought that the dished 

 wheel and bent axle are of a construction that tends to 

 reduce axle friction to a minimum. It is hoped that ex- 

 periments will be conducted at an early date to deter- 

 mine accurately the axle friction of wagons. 



358. Rolling resistance. Rolling resistance corre- 

 sponds to rolling friction in that it is due to the indenta- 

 tion or cutting of the wheel into the road surface, which 

 really causes the wheel to be rolling up an inclination or 

 grade. The softer the road bed the farther the wheel 

 will sink into it, and hence the steeper the inclination. The 

 height of wheel influences the rolling resistance in that 

 a wheel of large diameter will pass over an obstruction 

 with less power, as the time in which the load is lifted is 

 lengthened. There is also a less tendency upon the part 

 of a large wheel to cut into the surface, due to the larger 

 area presented at the bottom of the wheel to carry the 

 load. Elaborate experiments have been conducted by 

 T. I. Mairs, of the Missouri experiment station, in re- 

 gard to the influence of height of wheel upon draft of 

 wagons. Three sets of wheels were used with six-inch 

 tires and a net load of 2,000 pounds was used in all cases. 

 The total load for the high wheels was 3,762 pounds, 

 for the medium wheels 3,580, and for the low wheels 



The high wheels were 44-inch front wheels and 56-inch hind wheels. 

 " medium '* " 36 *' " " " 40 " " " 

 low " M 24 " " 28 " 



