SCIENCE OF THRESHING. 137 



THE TRACTION OR DRIVE WHEELS. 



The traction or drive wheels should be of sufficient 

 width of tire or tread to give good tractive power. 

 They are provided with spuds or lugs to prevent 

 slipping and are of a variety of forms. The larger 

 the traction wheel in diameter the more easily the 

 engine will traverse soft ground. 



A large wheel is less, liable to slip and revolve on 

 the ground as it has a greater bearing, owing to the 

 small angle of contact presented to the front side of 

 the wheel. 



