An inspection of the curves on figures 1 to 5 shows that there is ag 
constantly decreasing unit draft from the 14-inch through the 5-inch, J 
with an increased draft for the 6-inch tires in all cases, except that :, 
one representing the average of the third 10 trips. j | 
In conducting these experiments the road was constructed prior | 
to the first test by being plowed up, graded, and rolled. After each ff 
test and before the beginning of the next, the road was replowed, ~ 
graded, and rolled again, so that the condition of the road at the — 
beginning of each test was as nearly the same as it was possible to 
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Fie, 5.—Curve plotted from the results of traction tests conducted on a dry earth road. | 
Average of 40 trips. 
make an earth road. The trips selected for comparison are those in” 
which moisture and atmospheric conditions were practically the | 
same. | 
The long series of traction tests mentioned in the first paragraph fj 
includes investigation of the influences of many factors other than 
of tire width, and because of the magnitude of the work many of the 
results have not yet been calculated, but those that have been cal-_ 
culated conform very closely as to robe draft with those shown 
on figure 5, although the actual draft in pounds varies according jj 
to hee nature and condition of the road surface. i 
On ue 6 the horizontal distances are the pounds weight per | | 
inch of width of tire, as taken from curve on figure 5, while the | 
vertical distances are, as before, the unit drafts. 
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