1922.] 



The Shraavardine Tractor Trials, 1921. 



979 



Another difficulty which obtruded itself was illustrated by 

 the fact that the Renault machine, weighing 3^- tons when 

 drawing six furrows, had a tendency to lift in front. The 

 w T eight on the hind part of the tracks was therefore greatly 

 in excess of that for which the machine was designed. This effect 

 was of course due to the reaction of the driving torque on the 

 rear axle, and this is much greater in caterpillars than in 

 wheeled machines. 



Generally speaking, caterpillar tracks have up to the present 

 time been a source of some disappointment, especially to those 

 who claim on theoretical grounds that a track-laying machine 

 should have many advantages over wheel machines. So far, 

 where comparative tests have been made, these advantages 

 have not been strikingly manifested. 



Weight Distribution.— Another matter which calls for attention 

 is that of weight distribution and its effect upon slippage and 

 guidance of tractors. Slippage of tractors of different types, 

 with the same weight distribution and under practically the 

 same conditions, varied materially. This would indicate that 

 there are factors other than weight entering into the question 

 which need investigation. 



Poiver Rating. — As showing the wide differences between the 

 powers of the engines fitted to the various machines, it is noted 

 that the smallest engine is given as having been of 4.3 H.P. 

 and the largest 45 H.P. on the rating of the Society 

 of Motor Manufacturers and Traders. The highest maxi- 

 mum in the trial was the Hart Parr with 30 H.P. though 

 the Brtish Wallis was only a little way behind, while the 

 lowest was 6.25 developed by the Service machine. The trial 

 has indicated the wide variation existing in the rating of horse- 

 power. A vital need is felt for a scheme standardising the 

 power rating of tractors, as the present varying methods are 

 unsatisfactory to manufacturers and users alike. 



The trials demonstrated, as has been previously observed, that 

 although ploughs and other implements have been modified with 

 the object of taking advantage of the capacity of the tractor there 

 has been no work of a fundamental character with a view, for 

 example, to performing such work as ploughing at much greater 

 speed than, and excellence equal to, that done by the horse 

 plough. 



The economical speed of mechanical traction is more than 

 double that of the horse, and it appears that some of the most 

 elementary factors influencing the question have not been rightly 



b 2 ' 



