978 The Shrawardixe Tractor Trials, 1921. [Feb. 



Wheels and Caterpillars. — But little attention appears to have 

 been given to the essential problem of equipping wheels with 

 suitable devices to give the maximum adhesion under all con- 

 ditions likely to be met when field work may be required to 

 be done : one of the greatest disadvantages of the present- 

 day wheel equipment lies in the tedious methods which are 

 emplo}-ed for fixing or removing spuds. It should not be 

 difficult to introduce methods which would dispense with this 

 long and tedious operation. 



The draw-bar tests showed decisively how ineffective most 

 types were in giving satisfactory adhesion under certain con- 

 ditions, and it is a matter of surprise that greater attention 

 has not been paid to what is undoubtedly one of the principal 

 factors in tractor efficiency. 



The subject of caterpillar tracks is still very controversial. 

 *Articles on this subject have appeared in previous issues of the 

 Journal pointing out that investigation is necessary before any 

 definite opinion can be formed as to the respective merits of 

 caterpillar tracks and wheels. This view has been more than 

 justified as the result of the 1921 trials. If the draw-bar 

 test is to be taken as the criterion, the performance of the 

 chain-track machines was exceedingly good, since they deve- 

 loped a high draw-bar horse-power, whereas the wheel machines 

 could not develop a power commensurate with their rating; 

 yet at the Lincoln trials under other conditions track machines 

 failed where wheel machines succeeded. There is great need 

 therefore of ascertaining precisely and conclusively the relative 

 advantages of these two systems for different conditions. Pro- 

 gress would be facilitated if the following relations were 

 known : — 



(1) The bearing area and pressure distributed by wheels and tracks when 



the load is stationary and when in motion. 



(2) The theoretical form of spud or strake best suited for various broad 



groups of soils to obtain the best possible hold on the ground during 

 movement, taking into consideration the most important soil factors 

 within the range of practical ploughing. 



(3) The relationship between weight of the tractor and spud penetration . 



The real issue is to design a series of spuds or strakes which 

 will meet variable conditions in such a way as to use to the 

 fullest extent a minimum tractor weight together with the 

 minimum of energy and disturbance of the soil, secure the 

 maximum sensible area of contact, and still keep within the 

 shear value of the soil. 



* See the issues of this Journal for October. 1919, and November, 1920. 



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