It is a simple idea. As flat tires have become extremely rare, you might save approx. 25 kg for the spare tire. The space in the boot might very well be used for other things. The lower weight even saves some fuel. Still, safety is important. Just imagine a flat tire on the highway in the middle of road constructions. With runflat tires you may simply carry on in case of pressure loss, depending on the amount of rest pressure at least 50 km and probably more.
Both the PAX-System as well as the above displayed system do not reveal themselves when looking at the tire. The tire wall is obviously strengthened in the above pictures. The tire more less maintains its shape when the pressure drops; even with complete pressure loss it almost keeps its shape and thus prevents friction between flank and tread. Indeed, the system makes use of special wheel rims with higher humps, positioned somewhat more inwards, and with a stronger support towards the outside. Under normal circumstances, it provides less travel comfort, though. Yet, the process of shifting the suspension qualities away from the tire to the vehicle suspension is already going on since some time, especially due to the smaller cross sections of the tire. In addition, normal tires can be put on the changed wheel rims, later on, if desired.
Unfortunately, in reality a safe runflat-tire can become an unstable factor due to mistakes with the fitting of the tire. Normal fitting machines require that a large part of the bead is pressed into the drop center during the fitting process. And this is especially difficult with a runflat-tire with reinforced flanks. The regulation to lubricate the tire extensively and the rim well completely puts things right. Also the tire temperature may not sink below 15°C.
With a lot of experience the correct fitting is possible with a customary tire fitting system. It requires time, consideration, additional devices and clearly more force. If the assembly is performed incorrectly, the defects are hidden, unfortunately, behind/under the rim edge. If you are lucky, the tire pressure drops slowly. Much worse if it drops suddenly in a sharp bend. At least, there are special tire fitting systems for this kind of tires.
Please, never try to carry on with a flat normal tire, except to clear an immediately dangerous situation. You might have the idea to give up the tire which is maybe old anyways. Of course, you take the risk that the wheel rim will be damaged. If you should have likewise given up on the rim, the next danger is that the tire comes of the wheel rim. Extremely fearless people may still want to carry on, may be very slowly, as long as the car follows the steering movements. Please, think, however, that rubber on rubber creates a lot of heat from the friction. At first the tire will burn, then the inside fender, the outside fender and, in the end, the whole car will be in flames.
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