Emergency wheel system: Driving e.g. in a road-works area safer
It's not only all about the convenience in the event of a puncture, which, statistically seen, only happens once every ten years. The safety aspect also suffers, when inparticular, those who have little, or no experience with wheel-bolts, have to change a wheel. Then, there is also the space for the spare-wheel and the unnecessary weight which is transported over the years.
Always remove the sealing compound from the tyre afterwards
The side-walls of a tyre without the above shown insert would overheat through friction in a very short time, causing it's destruction, in the worst case, it could also set fire to the vehicle. Unfortunately the emergency wheel systems described below, increase the weight of the wheel by about 20%, thus, negatively influencing the unsprung mass. The spring response is also adversely affected, for the safety aspect however, a great advantage. E.g., one does not have to stop the car in single-lane road-works, thereby avoiding rear-end collisions. To ensure that the damage is noted, the combination with an Electronic tyre-pressure control, is especially advisable. To keep things in perspective, a word about the forerunner systems. One of these was the folding wheel which had it's place in the limited front boot of the Porsche 911. 10 years later it's slower 12-V-compressor was replaced by a compressed-air cartridge. Nowadays, we don't need the folding wheel any longer, and the air-pressure, together with the sealing compound, comes from a sort of spray-can. Compared with these, the following two systems, described below, are at an advantage. The PAX-system (see above figure) is based on a supporting ring, in this case, with a corrugated cross-section. This prevents the tyre-parts from touching each other, and allows,- the same as the Runflat -system - one to drive on for a further (as a rule 200kms) at at max. speed of 80 km/h. The supporting ring is mounted, together with the tyre, also on a special rim. In addition however, special mounting technology is necessary here. To fit on the rim in the first place, the inside diameter of the ring is a little bigger than the rim and it's outside diameter, a good deal smaller than the tyre. It supports itself on the wheel-rim through thick rubber rings.
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