Page:Motors and motor-driving (1902).djvu/273

Rh in converse ratio. What really kills the solid tyre, however, is speed, pure and simple, quite apart from the car or the passengers. Beyond a certain maximum rate of progression several factors combine to cause the solid tyre to leave the rim. The heat due to road friction, the pressure arising from the weight of the car, and the combination of centrifugal force with the weight of the tyre itself—much greater than that of a pneumatic—all create expansion and make the tyre rise from its bed and at times fly off bodily. A tendency to creep in the rim is also caused by the non-absorbent qualities of the solid as compared with the pneumatic tyre.

Given a combination of a heavy touring car with moderate speed, the use of solid tyres is practicable; and with a very heavy car, but of low speed, they may also be reasonably employed. But when the speed exceeds twenty miles an hour the solid tyre is inadvisable for more reasons than one, whatever the weight of the vehicle itself.

Of late a tendency has declared itself to effect a compromise on large cars of fair speed by fitting solid tyres to the driving wheels and pneumatics to the front. This method ensures facility of steering, and immunity from road shocks to the engine, and by the aid of long French springs the comfort of the passengers may be preserved, provided that the car is 'nursed' over specially rough surfaces. Even this compromise, however, has its limitations, and does not appear desirable for high-powered cars, unless the power is only used to the full on up gradients and considerably throttled down on level roads.

The types of solid tyre in use are not numerous. Perhaps the best known is the Clincher. The Sirdar and Capon Heaton are also favourably known. A tyre that has also been tried by a few British automobilists is the Falconnet (fig. 20), which is provided with a core of spongy rubber, and is thus somewhat less harsh than the entirely solid patterns. Experience