LIFE OF TIRES

Evening Post, Volume CIX, Issue 115, 17 May 1930, Page 26

LIFE OF TIRES

SOME USEFUL DATA

BEST WORKING CONDITIONS

It will be readily appreciated that howeyer perfect the production of a tire manufacturer there may be conditions applying to the use of the tire which may, adversely affect service, unless the manufacturer of the vehicle and the operator play their parts in ensuring that the tires with which the vehicle is fitted are used under the conditions the. tire manufacturer had in his mind,' the maximum period of service will not be achieved. The standards department of the British manufacturers' section of the S.M.M. and T. has already performed useful service by bringing to notice by means of its data sheets, the importance of correct tire inflation, and it has recently added to this by producing 1.A.8. data sheet No. 165, which deals with various factors in vehicle design tending to have an adverse effect on pneumatic tire wear, while the usefulness of this data sheet is increased by the recommendations therein for overcoming these factors. Toe-in. —The effect of. toe-in is to cause extremely rapid abrasive wear, and it is considered preferable that there should be no toe-in. Should toein be essential to steering design it is recommended that it should not exceed a total of l-Bin measured at the centre height of the tires. Camber. —The effect of camber is to cause rapid abrasive wear, often over the whole tread surface, but this wear is much more marked on the outside edge of the tread than elsewhere. The wear is of an uneven and patchy nature, the tread surface becoming pitted and undulating, the' effect being aggravated if the inflation pressure is permitted to fall unduly. Should toe-in be present also, the rate of wear may be many times the normal. To prevent that it is recommended that the wheels should be . set exactly vertical, but where camber is essential, it should not exceed 2 degrees per wheel and should be equal for both wheels. Twin Pneumatics.—Where twin tires fail to share the load equally, excessive wear will result, usually more severe on the inner tire. This leads to premature failure of that tire as compared with the outer one. It is recommended that to prevent this the centre-to-eentro distance between the twin tires should be no wider apart than is necessary to accommodate the correct size of tiro for the load. Pressures.—Correct pressures should

bo maintained for loads and tires should bo selected according to the mean of load schedules. These conditions have been set out under previous data sheets. Brake Drum Clearances. —Insufficient brake drum clearance in rear wheels, particularly with reference to commercial vehicles, results in any excessive heating of the brake drum being transferred to the tire, tube, and flaps. Tho tire aCected'is usually the inner one of a twin fitting, the outer one being only a few degrees above atmospheric tenrperature. The effect is often very severe, resulting in the rubber of the tire being practically destroyed, with complete disintegration of the tire edges and bead structure. This may occur at any stage of the life of the tire, consequent on variation in the conditions of usage. It is recommended that the minimum clearance between the brake drum and the underside of the rim s'lall be 7-Bin and that a clearance of 5-Bin shall be arranged between the bTake drum and tho rim in order to provide an air passage. _■ _It is further sifggested that the provision of simple means of frequently adjusting brakes is important, for it has been found that under certain operating conditions the difficulty of accurate adjustment may result in brakes being set too closely, causing undue heating, and not bearing equally on all wheels.