ON THE RESISTANCE OF ROAD VEHICLES TO TRACTION. 321 



pavement, with the setts too far apart, tlie resistance at trotting-pace is 

 more than that on good macadam, even with vehicles with the best 

 springs.' 



IX. ' The inclination of the line of draught, for the maximum useful 

 pull, increases with the resistance due to the surface of the road and as 

 the diameter of the fore- wheels diminishes. On the ordinary road the 

 inclination tends to the horizontal, so much as the construction of the 

 vehicle will permit.' 



These preceding facts were not always borne out by the experiments 

 conducted by General Morin, so he was requested by the ^Minister of 

 Public Works to undertake a further series of experiments in order to set 

 at rest the following questions : — 



I. Is the deterioration of the surface of the roads in inverse ratio to 

 the width of the tyres, with equally weighted vehicles ? 



II. Can vehicles be loaded proportionally to their width of tyres 1 



III. Is the deterioration of the road in inverse ratio to the diameter 

 of the wheels ? 



IV. Can vehicles be loaded in proportion to the diameter of the 

 wheels ? 



V. Which causes more damage to the road, a light dog-cart or a 

 country cart, both equally loaded ? 



VI. What is the rate of deterioration of roads in different states of 

 repair ? 



After a further series of experiments he replied as follows : — 



(i.) To say that it is legitimate to weight vehicles proportionally to 

 their width of tyres, assumes the hypothesis that the tyre jsresses equally 

 upon the ground throughout its whole width, which is not a correct basis. 



(ii.) Equally weighted wheels with tyres 0-06 m. in width deteriorate 

 the roads more than those with tyres 0'11.5m. to 0165 m. There is no 

 marked difference from 0*115 m. to 0-165 m. in width, so about 0115 m. 

 is the maximum. 



(iii.) A four-wheeled vehicle (waggon) with tyres 0'060 ni. in width, 

 diameter of fore-wheels l'3m., diameter of rear-wheels 1*5 m., can be 

 loaded up to 2,400 kilos in dry weather and 1,800 kilos in the rainy 

 season. 



(iv.) Vehicles equally loaded, and with the same width of tyre, deterio- 

 rate the road more as their diameter is decreased within certain limits. 

 The least diameter of the fore-wheels of a waggon should be 1 m. if it will 

 allow them to turn under the frame. This limit is fixed upon in order 

 not to raise the centre of gravity too high. The diameter of the wheels 

 can be decided upon with due consideration to the centre of gravity and 

 position of axle and frame. 



(v.) A load of 2,465 kilos drawn by a vehicle with tyres 2-029 m. in 

 diameter and in width 0-115 m., on a good macadam road, does not cause 

 any appreciable damage to the roads, even if the road be wet on the 

 surface. But a load of 5,000 kilos drawn on a cart with wheels 1-83 m. 

 in diameter and tyres 0-165 m. wide, or a load of 7,935 kilos drawn on 

 a four-wheeled waggon with tyres 0-16 m. wide and fore-wheels 1-011 m. 

 and rear- wheels 1-73 m. in diameter respectively, produces a considerable 

 deterioration upon the road. Therefore the load should not exceed 3,500 

 to 4,000 kilos. 



1902. T 



