368 



REPORT — 1903. 



plotted between tractive effort per ton and velocity (fig. 3) which is useful 

 for comparison with similar curves for wheels of different diameters. 



Additional experiments were made on pneumatic tyres under the 

 auspices of the Automobile Club of Great Britain and Ireland. For 

 these trials it was found that the car used by the Committee was not of 

 sufficient power ; a 24 horse-power Panhard and Levassor car was there- 

 fore temporarily used. 



It will be noticed in the photograph of this later car (fig. 6, Plate XI.) 

 that the springs .supporting the experimental wheel have been placed above 

 the frame, thus enaljling the centre of gravity of the trailer to be brought 

 very near to the ground. This alteration was found necessary owing to 

 a sidelong oscillation taking place at high velocities when the frame was 

 in the position as first arranged. The altered position proved quite 



Fig. 2. — Tract ive-efioit Velocity Curves for 24" x 2j" Pneumatic Tyre on Macadam. 



LBS 

 45 



S5 



15 



Velocity — Miles per lionr. 



successful, not the slightest oscillation of the trailer being noticed even 

 when heavily loaded and travelling at 3-5 miles per hour, which, it must 

 be admitted, is a fairly high speed at which to tow a wheel loaded with 

 a weight of 900 lb. 



Some difficulty was at first experienced in getting this car to pull 

 steadily at lower speeds, as the governor was constantly coming into 

 action owing to the full power not being required. This was finally over- 

 come by completely cutting out two of the cylinders, and thus reducing 

 the power of the car by half. 



These experiments were made with two sizes of tyres, one 34 inches 

 diameter by 3^ inches, and the other 34 inches diameter with a mean 

 diameter of cross-section of 4^ inches. 



