ON THE RESISTANCE OP ROAD VeBICLES TO TRACTION. 37B 



M. Jeantaud made some experiments on road resistance with an 

 electric vehicle. Such an automobile is eminently suited for this^ work, 

 on account of the perfect sensibility and absolute accuracy obtainable. 

 He used for these experiments a car having four equal wheels fitted with 

 Michelin tyres 840 by 90 mm. ; the front axles were 40-0 mm. diameter 

 and the back axles were of tempered steel on bronze hubs, the diameter 

 being 550 mm. The car with four persons weighed 1,780 kilos., or 3,925 lbs. 



At a speed of 15 kilometres per hour, or 9-32 miles per hour, this car 

 required a current of 22 amperes at 80 volts — that is, 1,760 watts. 



If 15 per cent, is deducted as the friction of the motor itself, the 

 energy of propulsion is 1,496-0 watts, or 149-6 kilogrammetres per second. 



Working this out in English units, we have a total tractive effort of 

 81 lbs., or 46 lbs. per ton. 



M. Jeantaud has calculated with Morin's formula and coefficients. 



First. — -The rolling friction, by the formula, 



in which /is a coefficient expressed in kilogrammes, varying with the 

 nature of the road and the width of the tyre, the value of / for a smooth 

 dry road being 0-010 ; F,. is the rolling friction ; P is the total load on 

 the vehicle in tons ; and D is the diameter of the wheel. 

 Second. — The axle friction by the formulae, 



in which s is a coefficient expressed in kilogrammes (varying with the 

 mode of lubrication and the nature of the rubbing surfaces) and being 

 taken as equal to 0-015. 



d is the diameter of the axle, and p the weight of the car without the 

 wheels. 



Adding these two resistances and multiplying the total effort by 4-16, 

 the velocity in metres per second corresponding to 15 kilometres per 

 hour, the work done per second is 182-274 kilogrammetres, or 1,320 ft. lb 



This figure would be that given for an iron-tyred vehicle, the only 

 kind employed at the time of M. Morin. According to M. Michelin, 

 the advantage obtained by using pneumatic tyres over iron tyres on a 

 road similar to the above would be at least 15 per cent. Taking 15 per 

 cent, off' the figure obtained, the work expended on traction is reduced 

 to 154-933 kilogrammetres, or 1,120 ft. lb. per second. This value is 

 very near to that actually obtained, viz. 1496 kilogrammetres per second 

 (1,084 ft. lb. per second), and this proves the correctness of the values 

 given for the coefficients /and *■. 



In January 1903 M. Jeantaud, with the same electric automobile, 

 between the bridges of Bineau and Neuilly, on a stretch of road just 1 kilo- 

 metre in length, showed that the tractive effiort for a road covered with 

 thick mud was, as General Morin found, quite double that on a dry road. 



On January 20, on the road in question, being then very muddy, the 

 track was covered on the third speed in 4 minutes, with a current of 

 30 amperes at 80 volts. In English units this would be a mean speed 

 of 9-32 miles per hour or 13*66 feet per second, with a total tractive 

 eflfort of 130 lbs., or 74 lbs. per ton. 



