Draft of Wagons. 



437 



tired wagon tended to fill up, the narrow wheeled wagon 

 gave the lightest draft. 



538. Size of the Carriage Wheel. It is plain from what 

 has been said, that on yielding road-beds the draft must 

 necessarily be heavier, other things being the same, the 

 smaller the wheels of the vehicle. This must be so both 

 because small wheels present less surface to the road-bed 

 to sustain the load, and because when the wheel has de- 

 pressed the surface it must move its load up a steeper grade 

 than the large wheel. It follows also from these state- 

 ments that wagons with small wheels must be more de- 

 structive to the road itself, whether this be of dirt, gravel, 

 stone or iron. 



Some unpublished data bearing upon this point are given 

 here by permission of Prof. T. J. Mairs of the Agr. Exp. 

 Stafion, Columbia, Ho. 



Wagons with three sizes of wheels were used in these 

 experiments : 



1. High, 44 inch front wheels and 56 inch hind wheels. 



2. Medium, 36 inch front wheels and 40 inch hind wheels. 



3. Low, 24 inch front wheels and 28 inch hind wheels, all having 

 tires 6 inches wide. 



The total load includir-g the wagon was : For 1, 3,762 ; 

 for 2, 3,580, and for 3, 3,362 pounds. 



The drafts in his trials are stated in the table below: 



28 



