ON THE RESISTANCE OF ItOAD VEHICLES TO TRACTION. 



3Q-. 



O-J 



Fifth Series of Tests, February 189G. 



All the tests liitherto have shown that the economy of pneumatics was 

 more apparent at the trot than at the walk. It can even be said that tlie 

 force taken by the pneumatic increased but little as the speed went up 

 from walking to trotting, whilst that absorbed by the iron perceptibly 

 increased with the speed. 



Experiments were made on a good regular macadam road ; length 

 100 m., gr. 1-5 per cent. Each test was repeated several times with an 

 empty vehicle, from which were deduced the following average speeds : — ■ 



For pneumatics . 4'900 km. per hour = walking speed ; 10-5 = trotting ; 



1512 = quick trot. 

 For iron . . . 4-550 km. per hour = walking speed; 10-94 = trotting; 



15-12 = quick trot. 



The averages of the forces exerted were as follows :— 



It will be noticed that at the trot and quick trot the results for pneu 

 matics are the same. It appears then that whatever the speed may be 

 within reasonable limits, the force absorbed by traction varies but little 

 upon good ground with pneumatic tyres. 



Tlien the advantage of the pneumatic over the iron tyres increases 

 with the speed. If we take 100 as the pneumatic traction, we obtain 

 for the iron traction at the ordinary trot 126 ; at quick trot 164. 



The following conclusions can be drawn from the above experi- 

 ments : — 



(i.) The solid indiarubber tyre is better than the iron in certain cases, 

 especially if the road be sticky, very irregular, or covered with snow, but 

 it becomes inferior to iron if the surface be hard and smooth. 



(ii.) Solid tyre vastly inferior to the pneumatic. 



(iii.) Pneumatic 50 per cent, better than the iron. 



Michelin compared his experiments with those of General Morin by 

 making a series of complementary tests with iron wheels upon good dry 

 pavement as much like the conditions under which General Morin's 

 experiments were performed as possible, with results as follows : — 



Walking = 

 Trotting = 



12-9 kg. 

 8-8 kg. 



These, on being compared with General Morin's, will be found in every 

 case below those given by him ; this is owing evidently to the better 

 hanging of the vehicle and the better dynamometer. 



But if we compare these various forces, taking for example 100 as 

 the force of traction at walking pace, we arrive at the following 

 results : — 



