No. C. DEPARTMENT OF AGRICULTURE. 991 



A difl'erence in the average of the two runs of 108.8 pounds. A 

 rain interrupted the experiment at this point, and prevented further 

 tests of the broad tires in their own ruts. 



(h) Clay road, wet and sloppy on surface, to depth of 3^ to 4 inches. 

 Hard and dry underneath. Both wagons cut through mud, no ruts 

 left. Trial made October 13, 181)0. Length of run, 4UU feet. 



Average draft. 



Narrow tire, 28G.5 pounds. 



Broad tire, 400. 3 " 



Dilierence in favor of narrow tire, 110.8 " 



Percentage dilierence in favor of narrow 



tire, 41.8 



In ever}' trial on a soft surface overlying a hard roadbed, the 

 narrow tires show to an advantage. This advantage reaches its 

 maximum when the soft covering of the road consists of sticky clay. 

 Such a condition is met frequently for short periods in the spring, 

 summer and fall, immediately after rain has fallen on a hard, dry 

 road or when the road has thawed on the surface and remains frozen 

 underneath. As explained in the case of the wet gravel road and 

 dusty dirt road, this dilierence appears to be due to the fact that the 

 narrow tires cut through the mud and roll on the hard roadbed 

 underneath with very much less resistance than is encountered by 

 the broad tires. In the nature of the case this condition of the road 

 surface is of short duration. A few hours of sun will sufficiently 

 dry this mud or sand so that it will pack under the broad tires in- 

 stead of being pushed aside. In that condition the narrow tire is 

 at its greatest disadvantage as compared with the broad tire as is 

 clearly shown in the next trial on a dirt road drying on top. 



(i) Black soil. Graded late in fall. Mud stiff and drying on top. 

 Narrow tire made rut 3. .5 inches deep in passing over the surface 

 twice. Mud packed under the broad tires leaving scarcely any rut. 

 Length of run, 400 feet. March 19, 1897. 



Average draft. 



Narrow tire, 497.0 pounds. 



Broad tire, 30G.9 " 



Dilierence in favor of broad tire, 100.1 " 



Percentage difference in favor of broad 



tire, 01.6 " 



(j) Clay road. Dry on top. Spongy underneath. A new track 

 was made, the narrow tire being run first, the wide tires running over 

 the rut cut by the narrow tires. Depth of rut made by narrow 

 wheels, from 8 to 12 inches. Rut of wide tires 4 to 6 inches deep. 

 Trial made February 28, 1890. Two runs. Length of runs 400 feet. 



