ON THE RESISTANCE OF ROAD VEHICLES TO TRACTION. 375 



the front .axle on a single transverse spring, thus reducing the number of 

 springs on the car to three. 



When the springs have been depressed by an obstacle in the roadway, 

 they only return to the position of equilibrium after a number of oscilla- 

 tions of decreasing amplitude have taken place. It is advisable to spare 

 the vehicle this continued oscillation, as at high speeds it causes the 

 wheels to leave the ground, and consequently reduces the effective power 

 of the motor. M. Truffault has taken out a patent for an arrangement 

 to remedy this defect. The friction between two metal surfaces prevents 

 the oscillations from arising. He tried a spring fitted with this damping 

 action on a quadricycle, which carried his son to victory over the kilo- 

 metre at Deauville in 1901. This spring has given very good results, 

 enabling one to travel rapidly even over the worst of paved roads. 



Effect of the Katvre of the Tyres. 



The experiments of M. Michelin have shown that the tractional 

 resistance is reduced from 15 per cent, to 30 per cent., according to the 

 nature of the road, by the use of pneumatic tyres in place of metal 

 tyres. He explains this by the well-known saying, ' Le pneu boit 

 I'obstacle.' Baron de Mauni in a recent work has given an account of 

 some experiments which he made on different tyres, particularly pneu- 

 matics. He showed that if two wheels with tyres of equal widths 

 supported equal loads, the one that has the greater arc of contact with 

 the ground will travel better than the other. With a rigid tyre such 

 extended contact can only be secured by increasing the diameter of the 

 wheel, which is impossible beyond certain limits, so that the tyre will 

 sink into the ground by an amount proportional to the weight carried. 

 With rubber tyres the increased area of contact is due to the elasticity of 

 the material and not to the increased diameter, so that the wheel does 

 not sink into the road. 



Professor Baker's experiments seem to show that on good roads the 

 width of tyre has little effect on the resistance, and that even on bad 

 roads the advantage lies sometimes with the wide tyres and sometimes 

 with the narrow ones, according to circumstances. Arguments have been 

 advanced in favour of both wide and narrow tyres, but nothing very 

 definite seems to be known on the subject ; according to M. Michelin, 

 if we reduce the width of the tyre we reduce the adhesion to the ground, 

 which is already little enough. As a case in point, he mentions that 

 M. Serpollet, in order to attain a speed of 120 kilometres (75 miles) per 

 hour on the Promenade des Anglais in 1902, had to deflate his tyres, and 

 thus get a larger surface of contact with the ground. Besides, in order 

 to get a narrow tread it is necessaiy to give to the tyre a form other than 

 circular, and this shape can only be retained at the expense of its flexi- 

 bility. Consequently a tyre of this description will be subjected to greater 

 internal friction in its fabric than one naturally circular in section, and 

 the energy wasted will be therefore greater. 



The whole question, however, is very much open to discussion, and the 

 present Congress may offer to the opposing schools an opportunity of 

 coming to some understanding. 



Resistance of the Air. — Study of Forms to diminish tJiis Scsistance. 



The air resistance is a retarding force of the highest importance, 

 especially where speed is concerned, and there is unfortunately great 



