ON THE RESISTANCE OP ROAD VEHICLES TO TRACTION. Sid 



was made on September 5 on a level stretch of macadam road passing 

 through Ince "Woods, near Sefton. The surface was in fairly good 

 condition, slightly wet in places. 



With these series of experiments a run \Vas made with a given load 

 at a constant speed to a spot about ^ mile from the starting-point. The 

 return run was made at the same speed. With the same load a higher 

 speed was then taken, and so on, so that for each load readings were 

 taken at about 6^, 8, 10, and 14 miles per hour: This method of pro- 

 cedure was followed for each load carried. The leverage used was 4 to 1, 

 and the loads were respectively 315, 427, 539, and 651 lb; 



Wall-diagram No. 5 showed the tractive-effort-velocity curves for each 

 load. It was noted that the tractive effort was dii-ectly proportional to 

 the load, but increased very slightly with the velocity. This Was what 

 was observed by M; Michelin in his experiments. 



Wall-diagram No. 6 showed a curve plotted between tractive effort 

 and load for the above. It being a straight line showed that the tractive 

 effort was directly proportional to the load. 



Wall-diagram No. 7 gave the four curves of diagram No. 5 plotted 

 as tractive effort per ton. 



A specimen of the graph was reproduced on a large scalfe as a wall- 

 diagram to show the nature of the curve obtained. In the experiments 

 which have been made as yet, only level roads have been tried ; and it 

 was not possible on a level I'oad, dragging the wheels behind, to experi- 

 ment satisfactorily with speeds of more than 15 miles per hour with the 

 present car. For higher readings than this experiments will be con- 

 ducted on an incline of such a gradient that a positive reading is 

 recorded on the dynamometer, so that to find the pull on the wheel for 

 the velocity it is only necessary to add to the registered pull the com- 

 ponent of gravity parallel to the surface in question. By this means it 

 will be possible to reach speeds up to 30 miles per hour. 



Behaviour of Apparatus. 



The behaviour of the apparatus is on the whole ^•ery satisfactory. 

 The experimental wheel runs very steadily behind the car, even with 

 heavy loads at high speeds. The lurry wheel, however, runs better on 

 setts than on macadam, as it oscillates sideways somewhat when passing' 

 over the latter at a high speed. The pneumatic-tyred wheel runs exceed- 

 ingly steady over all roads at all speeds. 



The pneumatic cushion answers very well. It allows the instrument 

 to swing gently from side to side in place of being subject to the violent 

 vibration set up by the shaking of the car, due both to the engines and 

 to rough roads. 



The results just given were all it was possible to obtain during the short 

 time before the meeting that the apparatus has been available, but it is 

 hoped that during the ensuing year reliable and valuable results may be 

 obtained, although, of course, to get a complete series of results under 

 all conditions must necessarily involve an immense amount of time and 

 labour, as with so many variable quantities the changes could be run"- on 

 them ad infinitum. 



Plate V I. (figs. 1 , 2, and 3) shows photographs of the dynamometer ready 

 for use, Plate VII. (figs. 1 and 2) views of the recording instrument. 



