200 



ENGINEERING ON THE FARM 



over it. A narrow tire has a tendency to cut the road 

 covering and cause the surface to be more susceptible to 

 water. The effect of the width of the tire on the tractive 

 force depends entirely upon the condition of the road or 

 the land surface over which the vehicle is passing. The 

 wide tire is better so long as it does not cut into the surface, 

 but when the load is sufficiently heavy to force the tire into 

 the ground the narrow tire runs more easily. Experiments 

 along this line indicate the following: On good hard roads 

 and pavements there is no argument in favor of the wide 

 tires; rather in favor of the narrow ones. On soft mud 

 and slush where the tire will cut, a narrow tire is better; 

 on soft ground or on sod the broad tire is the better, as it 

 will carry a greater load without cutting. As a general 

 statement it may be said that the broad tires keep the 

 road in better condition and do not increase tractive resist- 

 ance to a serious extent. 



Width of Tire as Recommended for Wagons of 



Different Carrying Capacity by the Bureau 



of Public Roads, United States 



Department of Agriculture 



Diameter of wheel. Experiments made to determine a 

 satisfactory diameter of a wheel indicate that high wheels 

 are best under nearly all conditions, but they are likely to 

 become cumbersome, a fact which limits the diameter that 

 may be used. The best height of wheel, considering con- 

 venience and tractive force, is one with a diameter of 30 to 36 

 inches for the front wheels and 40 to 44 inches for rear wheels 

 placed on axles of equal length. Small wheels increase the 



