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Run-Flat tyres
A run flat tyre is a tyre that is designed to resist the effects of deflation and to enable the vehicle to continue to be driven - albeit at reduced speeds (i.e. 80 km/h) and for limited distances (80 km).
All of the major tyre manufacturers offer a run flat tyre of some kind. There are three basic technologies available:
The tyre is built with stiffer side-walls that can bear the weight of the vehicle even when the pressure within the tyre 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 tyre 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 tyres 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 tyres if the puncture is in the side wall or near the edge of the tread.
Self-Sealing
Self-sealing tyres are designed to fix most tread-area punctures instantly and permanently. These tyres feature standard tyre construction with the exception of an extra lining inside the tyre under the tread area that's coated with a puncture sealant that can permanently seal most punctures from nails, bolts or screws up to 3/16 of an inch in diameter. These tyres first provide a seal around the object when the tyre is punctured and then fill in the hole in the tread when the object is removed. Because these tyres are designed to seal the tyre immediately upon being punctured, most drivers will never even know that they just had a puncture. Also because these tyres feature standard tyre constructions, the traditional loss-of-air symptoms that accompany a flat tyre remain to warn the driver if the tyre is damaged beyond repair. Therefore, self-sealing tyres do not require a low air pressure warning system.
Example: Continental ContiSeal.
Self-Supporting
Self-supporting tyres feature a stiffer internal construction, which is capable of temporarily carrying the weight of the vehicle, even after the tyre has lost all air pressure. To provide "self-supporting" capability, these tyres typically attach rubber inserts next to or between layers of heat-resistant cord in their sidewalls to help prevent breaking the reinforcing cords in the event of loss of air pressure. They also feature specialized beads that allow the tyre to firmly grip current Original Equipment and aftermarket wheels even in the event of air loss. Because self-supporting tyres are so good at masking the traditional loss-of-air symptoms that accompany a flat tyre, they require a tyre pressure monitoring system to alert the driver that they have lost air pressure. Without such a system, the driver may not notice underinflation and may inadvertently cause additional tyre damage by failing to inflate or repair the tyre at the first opportunity. Typically, self-supporting tyres maintain vehicle mobility for 50 miles at speeds up to 55 mph.
Examples: Bridgestone RFT (Run Flat tyre), Dunlop DSST (Dunlop Self-Supporting Technology), Firestone RFT (Run Flat tyre), Goodyear EMT (Extended Mobility Technology), Kumho XRP, Michelin ZP (Zero Pressure), Pirelli RFT (Run Flat Technology) and Yokohama Run Flat.
Auxiliary Supported Run Flat Systems
Auxiliary supported systems combine unique wheels and tyres used for Original Equipment vehicle applications. In these systems, the flat tyre's tread rests on a support ring attached to the wheel when the tyre loses pressure. The advantage to this type of system is that it will place most of the mechanical task of providing run flat capability on the wheel (which typically doesn't wear out or need to be replaced), and minimizes the responsibility of the tyre (which does periodically wear out and requires replacement). Additionally, auxiliary support systems promise better ride quality because their sidewall's stiffness can be equivalent to today's standard tyres. The disadvantage to auxiliary supported systems is that their unique wheels will not accept standard tyres and that their lower volume will make this type of system more expensive.
Example: Michelin's PAX System wheels and tyres
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