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A New Rim for Large Pneumatic Tyres.

7th September 1926
Page 60
Page 60, 7th September 1926 — A New Rim for Large Pneumatic Tyres.
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Which of the following most accurately describes the problem?

A" NV form of demountable pneumatic tyre rim has been introduced in the United States of America by the

Goodyear Tire and Rubber Co., which is claimed to be suitable for the wheels of buses. Among the principal advantages advanced in favour of the form of construction are, first, a reduction of the unsprung weight ; secondly, simplification of tyre mounting either for single or twin tyres; and, thirdly, a saving of time and labour in tyre changing.

T h e sectional drawing shows a straight-sided pneumatic tyre in outline mounted on the new rim and locked into position. The rim consists of the base, one' side flange and, at theopposite edge, a lip :which has a reverse oe inward taper upturned at its very edge to catch the endless lock ring.. This rim is split. The lock ring is endless . and has . the remaining side flange and a circular tongue to engage in the upturned edge of the rim lip. The felloe is bevelled and is provided at intervals with lugs fornied integrally with it, each having a threaded stud on to which are screwed the locking nuts.

The various parts, so we are informed, are designed to permit of interchangeability of 5-in. to 8-in, rims on the same felloe.

In mounting, the tyre is placed on the split rim and the . endless lock ring is then put over the contracted edge of the rim lip. The tyre and, rim then being mounted on the felloe, the action of driving the rim On to the bevelled feline by means of the ants expands the rim and clamps it between the two bevelled faces—the one on the ,felloe and the other on the endless lock ring, a slight gap occurring in the side flange when the rim is split.

The endless lock ring can only be removed when the rim and tyre have

The

been demounted, because not until then can the rim be contracted sufficiently to allow the lock ring to pass over the lip of the rim. It is asserted by the producers of this rim that in order to remove the tyre from the split rim the only tool required is a heavy screwdriver, with which one lip of the split rim can be depressed or contracted, and that neither tyre jacks nor clamps are necessary. This is a point which will appeal to commercial users_

In the ins.-allation of twin tyres a simple method has been devised, but, so far, full and lucid details are not to hand in this country. It would seem, however, that the rim of the inner tyre bears on the bevelled felloe as already

described. An endless rolled-steel spacer separates the two rims, which are mounted with their endless locking rings facing each other, or the felloe lugs are formed integrally and inwards. Towards these are drawn a bevel ring which bears on the inwardly turned lip of the rim of the outer tyre, thus expanding it against its locking ring and at the same time drawing it tight towards the inner tyre,

the travel in that direction being checked by the spacer ring. Channels are formed in the •felloe and valve stem extensionsare used to bring both valve caps through holes placed at the middle of the felloe and of the spacer.

Considerable attention has been paid by the designers to the need for clearing existing sizes of brake drums on bus wheels. The type of drum which is favoured is that which has ribs turned on the outside and in which as a consequence there is increased air-cooling space between the drum and the tyre rim.

In the ease of some forms of brake drum much of the heat generated when heavy braking is rendered necessary is sometimes carried to the wheel rims and merely aggravates the difficulty of keeping tyres cool. Even without this increase in heat, that generated in the tyres thenthelves, .partly owing to the friction in the walls when the tread is depressed and partly due to friction between, the tread and the road surface, is often quite Considerable, particularly where comparatively high speeds are maintained as a matter of course for long

distances. •

There are other reasons for the employment of ribs on brake drums. They obviously strength'en. the drums and prevent any risk of these fracturing through being worn excessively thin. The rims also do much to prevent brakedrum chatter.

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