338 



REPORT — 1902. 



Agricultural Waggon . 



Agricultural Cart 



of Waggon 

 or Cart 

 in lbs. 



m 



tons 



Tractive | Tractive 

 Force per | Force per | 

 ton of Load ton of Load 



on Turf 



2,142 



1,895 

 1,813 

 1,752 

 1,281 

 1,435 

 1,235 

 1,278 

 1.3.30 

 1,379 

 1,148 



3 

 3 

 3 

 3 



u 



235 



277 

 289 

 227 

 2t59 

 260 

 332 

 240 

 253 

 248 

 235 



on Boad 



148 

 125 

 139 

 170 

 116 

 147 

 111 

 109 

 130 

 153 

 108 



XI. Investigations of Jra 0. Baker, M.Am.Soc.C.E. (1902). 

 The resistance to traction of a vehicle upon the road consists of three 

 independent elements : I. Axle friction ; II. Rolling resistance ; and 

 III. Grade resistance. Nothing need here be said about grade resist- 

 ance, since it is perfectly understood that it is equal to 20 lb. per ton 

 for 1 per cent, of grade. 



I. Axle friction. — It has nothing to do with the surface of the road. 

 The coefficient of friction varies with the material of the journal and its 

 bearings, and with the lubricant. It is nearly independent of the 

 velocity, and according to the author's experiments seems to vary inversely 

 as the pressure. 



For light carriages when loaded the coefficient = 0020 ' of the weight on axle. 

 For heavier . „ „ „ „ = 0015' ,, „ 



For American thimble skein waggon „ =0012' „ „ 



If there is a deficiency of lubricant, these figures are two to six times 

 greater. General Morin's value for axle friction was 0-Q&^ ; this difference 

 is probably due to the better mechanical construction of the present day. 

 The tractive force required to overcome the axle friction is about 3 to 

 3^ lb. per ton of the weight on the axle for ordinary waggons, and from 

 3 J to 4^ lb. for waggons with medium-sized wheels and axles. 



II. Rolling resistance. — The resistance of a wheel to rolling is due to 

 the yielding or indentation of the road, which causes the wheel to be 

 continually climbing an inclination. The resistance is measured by a 

 horizontal force necessary at the axle to lift it over the obstacle, or to roll 

 it up the inclined surface. The rolling resistance varies with :— (a) The 

 diameter of the wheel ; {h) The width of the tyre ; (c) The speed ; 

 {d) The presence or absence of springs on the vehicle ; (e) The nature 

 of the road surface. 



(a) The diameter of the tvheel. — The rolling resistance varies inversely as 

 some function of the diameter of the wheel, since the larger the wheel the 

 greater ^ the foi'ce required to pull it over the obstacle. 



The results of the experiments are shown in Table I., data as follows ; 



The three sizes of wheels used : (44" in front and 56" hind wheels) = 50" wheels. 

 ., „ „ (36" in front and 40" hind wheels) = 38" wheels. 



„ „ „ (24:" in front and 28" hind wheels) = 26" wheels. 



The load being IJ ton of 2,000 lb. per ton and with tyres 6" wide. 



' The above figures assume good lubrication. 



- Less. 



