252 



FARM MACHINERY 



ing conditions : (a) When the earth road was muddy, 

 sloppy and sticky but firm underneath, (b) when the 

 mud was deep and adhered to the wheels, (c) when the 

 road was covered with deep loose dust, and (d) when 

 the road was badly rutted with the narrow tire. 



INFLUENCE OP WIDTH OP TIRE UPON DRAFT* 



Draft in Pounds per Ton 



Besides the reduction of draft attained in the majority 

 of cases with the use of wide tires, there is another im- 

 portant advantage from their use, as there is less ten- 

 dency to rut and destroy the road surface. It is be- 

 lieved that this feature should be placed before all others. 



There is a slight increase in draft with an increase in 

 speed. Morin, who conducted experiments to determine 

 the relation between draft and speed, found that the draft 

 increased about as the fourth root of the speed. The 

 draft upon starting a load is greater than after motion 

 has been attained, and is due to the settling of the load 

 into the road bed, the increased axle friction of rest, and 



* Missouri Agricultural Experiment Station, Bulletin No. 39, 1897. 



