Fail-safe wheels are mainly used on special vehicles that have to remain functional in difficult terrain or under fire. Most fail-safe wheels rely on a variation of the classic pneumatic tire for this purpose, which can continue to be used as a tire with emergency running properties even if it is damaged; in some cases, an airless tire is also used.
Tires with run-flat properties, for example, use self-sealing foam or multi-chamber systems to remain stable even if an air-filled chamber is damaged. Inlays on the inside of the tire, consisting of steel belts or plastic fabric, can also reinforce the tire. Other ways of supporting the tire in the event of a loss of air include a non-slip design of the interface between the tire and rim, and special structures on the rim on which the tread can be supported. All methods serve to avoid unnecessary stresses caused by thermal influences or flexing movements in the event of damage. Many cars with vehicle armoring are equipped with these types of tires.
In addition to these relatively simple solutions, there are also technically more complex tires with run-flat properties: Tire pressure regulation, for example, requires a compressor that compensates for minor damage by supplying air. This technology can be combined with a sealing system in which cracks or holes are sealed with a special liquid.
For military use in combat, however, it is possible that these solutions will not be sufficient either. Fail-safe wheels for this purpose therefore consist of plastic or metal structures in extreme cases, which still deflect but are not dependent on air inflation. Military vehicles or other vehicles operating under extreme conditions in particular are equipped with such tire systems.
