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Rh of the removal with one lever depends upon the size and age of the tyre; two levers are in most eases to be preferred.

To save time on the road it is usual to remove the air-chamber bodily and replace it with a new one, deferring the repairing of the puncture to a more convenient occasion. In this case the valve should be loosened by unscrewing the large nut and rubber washer, and pushing the stem upwards until it leaves the rim. The air-tube should then be detached all round with the fingers, great care being exercised lest the rubber be adhering to the lining of the cover, owing to an insufficiency of chalk having been employed when the tube was last fixed, and also lest, as is very probable, the nail, flint, or

other puncturing instrument, be still lodged within the cover, in which case ungentle handling may tear the tube. If the cause of the puncture be found, or even if there be a visible cut right through the cover, the corresponding spot on the tube should be determined, when a hole will probably disclose itself if the rubber be slightly stretched. The puncture should at once be marked with a coloured Fig. 9 pencil, whether the tube is to be repaired forthwith or not. Then remove the nail, or other cause of damage, from the cover without fail.

If no spare tube be available, and the one in situ must be mended there and then, it is not necessary to loosen the valve in the first instance, as the puncture will probably be easy to locate, and may be at such a distance from the valve as to render a repair feasible without removing the entire tube. If the valve has to be detached, however, and the cover is of 90 mm. diameter or more, the lever with three projections should be employed, as in fig. 10, to hold up the cover.

To Repair a Puncture.— This process is simple. Select a