312 



POWER AND THE PLOW 



It will be noted that the percentage of variation in draft 

 between different road surfaces is not so great as for wagons; 

 also that the draft ranges from about 160 to 225 pounds per 

 gross ton. These drafts per ton are higher than are usual with 

 wagons, and may be partly ascribed to the greater internal 

 friction. A ton of engine weight pulled about 19 per cent, 

 harder than a ton of wagon and load at the Winnipeg motor 

 contest of 1909. The speed of travel for the tests reported 

 in this table was 1.95 for macadam; 1.93 for firm dirt; 1.77 for 

 soft, muddy road, and 1.67 for the soft field. The tractor 

 pulling this load was designed to run at 2.05 miles per hour 

 on low gear, hence the slippage under the various conditions 

 ranged from about 5 to 18.5 per cent. If a constant figure for 

 friction of gearing, etc., were subtracted from the draft per 

 gross ton in each case, and for the better surfaces possibly a 

 trifle more in proportion as the speed increases, the difference 

 in draft due to road surface would be more strongly emphasized. 

 On grades, the friction and ground resistance are constant, for 

 all practical purposes, variation being due to the lift on the 

 tractor alone. In actual pulling, the internal friction would be 



