The major safety benefit of Run Flat Technology or RFT is that it enables a driver to maintain control if a vehicle in motion suffers a rapid loss of tire pressure. In addition, RFT tires enable the driver to continue the journey within specified speed and distance limits, avoiding the need to replace the wheel on the side of the road.
Tire manufacturers also maintain that as an added benefit of RFT they usually save weight by eliminating the need to carry a spare tire. However, because of their construction they are generally between two to three times heavier than their conventional counterpart, which adds un-sprung weight to the vehicle, affects the suspension, and can increase fuel consumption.
Because of the extra materials used in construction of the tire, they are also normally more expensive to purchase. In addition, runflat tires are usually “harder riding” and noisier in operation which can be a disadvantage in some applications. From a manufacturing perspective however, the free space created by eliminating a standard spare wheel gives the car manufacturer a range of additional design opportunities.
An “onboard” vehicle tire pressure monitoring system (TPMS) is normally mandatory for all RFT applications.
Run Flat Technology design features generally focus on two aspects of operational use - rigidity and heat resistance. This is to enable the tire to support vehicle weight when it is rotating with a total air loss. The sidewall is constructed with reinforced rubber and is thicker than in conventional tires enabling it to carry the vehicle's weight at zero-pressure.
While the bead shape configuration of the tire itself is largely unchanged to enable compatibility with conventional rims, the bead wire is normally wider and reinforced to ensure a secure fit on the rim even at zero pressure, and a special bead filler with low heat generation is used as part of the construction.
Some runflat tires are known as “Extended Mobility Technology” or “EMT” tires. EMT sidewalls can be six times thicker than traditional tires. As a result the manufacturers say that EMT runflat tires can be driven at speeds of 50 miles per hour or 80 kilometers per hour for up to 200 miles or 320 kilometers in a deflated condition before being damaged. They normally have a directional tire pattern which must be fitted in such a way that the tread rotates only in one direction.
Specialized equipment is needed to fit runflat tires as the sidewalls are stiffer and thus not as pliable when fitting. Some heavy-duty applications have a two-part wheel arrangement with a thick rubber expander fitted inside the tire before the two halves of the wheel are bolted together.
Whilst the tires are described as “Runflat", they are not indestructible. Major damage that slices the tire casing can still result in complete tire failure.
