Run flat tires
A run flat tire is a pneumatic vehicle tire that is designed to resist the effects of deflation and to enable the vehicle to continue to be driven - albeit at reduced speeds and for limited distances.
All of the major tire manufacturers offer a run flat tire of some kind. There are three basic technologies available:
Self Supporting Construction
The tire is built with stiffer side-walls that can bear the weight of the vehicle even when the pressure within the tire is greatly reduced. The side-walls are typically constructed of layers of rubber and a heat-resistant cord that prevent the side-walls from folding or creasing. The bead around the edge of the tire is also specialised to grip the wheel rim such as to avoid becoming detached from the rim.
Self-supporting run flats are fairly common on light trucks and passenger cars and typically provide for the vehicle to drive for 50 miles at around 50 miles per hour. However, if the tires are treated to this kind of punishment, they may still be irreparably damaged in the process.
There are also issues with repairing punctures in run-flat tires if the puncture is in the side wall or near the edge of the tread.
The first vehicle ever to be sold with run-flat tires was the Mini 1275GT in July 1974. It used the Dunlop Denovo system which required special wheels and featured ultra-low profile side-walls.
Self-Sealing Tires
These tires contain an extra lining within the tire that self-seals in the event of a small hole due to a nail or screw penetration. In this way, the loss of air is prevented from the outset such that the tire is either permanently self-repairing - or at least loses air very slowly.
Auxiliary Supported Tire/Wheels
In this system, there is an additional support ring attached to the wheel that can support the weight of the vehicle in the event of a loss of pressure.
The requirement to have both special wheels and special tires limits the ability of these systems from becoming widespread.
See also
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