Run-flat tyres are simply tyres that have been designed to permit your vehicle to continue being driven (albeit at a reduced speed) for a certain distance after incurring a puncture. They can be self-supporting, auxiliary supported or self-sealing, and the idea behind them is that it gives you time to drive to a convenient place to replace the tyre.
- Self-supporting: These usually allow the car to be driven at about 50mph for up to 50 miles. They feature thicker side walls to allow them to be driven with no air in, but the extra weight means lower rolling resistance/fuel efficiency. Bridgestone manufactures run flat tyres like this, and they are fitted as original equipment on some new BMWs.
- Auxiliary supported: These need to be fitted to wheels that have an additional support ring to support the vehicle in case of a puncture. If your car comes fitted with these wheels, then (unless you change the wheels!) you have to fit the right sort of run-flat tyres to them. Additionally, driving on them for too long can damage the wheel resulting in even more expense.
- Self-sealing: These tyres feature an additional lining that will seal itself if it is punctured by a nail or such-like. The idea behind these is that air loss is kept to a minimum. Some punctures will effectively be self-repairing, while others will just lose air slowly. You can also purchase tyre sealants to work in a similar way. These are injected through the tyre valve.