Run flat tires
Encyclopedia
A run-flat tire is a pneumatic
vehicle
tire
that is designed to resist the effects of deflation when punctured, and to enable the vehicle to continue to be driven at reduced speeds (up to 90 km/h or 55 mph), and for limited distances of up to 100 miles (160 km), or even 200 miles (320 km) depending on the type of tire.
In 1934, the Michelin Tire Co.
, France, introduced a tire that was based on technology developed for local commuter trains and trolleys. It had a safety rim inside the tire which if punctured would run on a special foam lining. The tire was sold for military use and for specialized vehicles like bank armoured cars. It was advertised as "semi-bullet proof". While the tire performed as advertised it was far too expensive to be a feasible option for private automobile users.
In 1958 Chrysler
and US Royal
offered run-flat tires using an interlining to carry the weight. Bridgestone run-flat tires are supplied on most new model BMW
cars. BMW promoted these as a safety feature and as an alternative to carrying a spare tire.
Self-supporting run-flat tires are now 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 subject to this kind of misuse, they may become irreparably damaged in the process. In addition, if the tire is punctured in the sidewall or at the edge of the tread, repair may be impossible or unsafe. These tires typically carry a 15% - 27% weight penalty over similar standard tires, or additional 2–3 kg (4-7 lb). The additional mass concentrated on the outer edge of the wheels can impose a significant performance penalty due to greater rotational inertia and unsprung mass.
. 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.
There are also a number of retrofitted tire sealant
s which act in a similar way to self-sealing tires. These compounds are normally injected through the tire valve
. The rotating force then distributes the compound onto the inner surface of the tire to act as a self-sealing lining within the tire.
, in part due to their added structural material and mass. On the other hand, internal bracing in some run-flat tires reduces deformation, with the opposite effects of reducing rolling resistance and improving fuel efficiency.
Further advantages are derived from not needing to carry a spare wheel: The space can be used for other purposes. Also, the absence of a spare wheel contributes to lower vehicle weight which will in turn reduce fuel consumption, reduce harmful exhaust emissions, improve performance, handling and braking characteristics. However, these may be negated by the increased weight of the tires if they are self-supporting.
Due to reinforcement in tire side walls, run-flat tires usually give firmer rides compared to conventional tires.
Standards of Performance
The primary benefit of using run-flat tires is continued mobility in case of a loss of air pressure, either due to a 'normal' puncture or a hostile deliberate act or even a bullet shot while the vehicle is travelling at high speed. Performance criteria are therefore in terms of distance and speed at which the vehicle can escape without becoming immobile and the steering control over the vehicle during this process.
The usual standard of performance, especially for military or security vehicles, are the Finabel
standards.
Pneumatics
Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...
vehicle
Vehicle
A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....
tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
that is designed to resist the effects of deflation when punctured, and to enable the vehicle to continue to be driven at reduced speeds (up to 90 km/h or 55 mph), and for limited distances of up to 100 miles (160 km), or even 200 miles (320 km) depending on the type of tire.
Self-supporting
The origins of the commercial self-supporting run-flat tire started in 1935 with a tire that had a fabric inner tire. The tire was advertised as a protection against blow outs, a common and very dangerous occurrence in the 1930s..In 1934, the Michelin Tire Co.
Michelin
Michelin is a tyre manufacturer based in Clermont-Ferrand in the Auvergne région of France. It is one of the two largest tyre manufacturers in the world along with Bridgestone. In addition to the Michelin brand, it also owns the BFGoodrich, Kleber, Riken, Kormoran and Uniroyal tyre brands...
, France, introduced a tire that was based on technology developed for local commuter trains and trolleys. It had a safety rim inside the tire which if punctured would run on a special foam lining. The tire was sold for military use and for specialized vehicles like bank armoured cars. It was advertised as "semi-bullet proof". While the tire performed as advertised it was far too expensive to be a feasible option for private automobile users.
In 1958 Chrysler
Chrysler
Chrysler Group LLC is a multinational automaker headquartered in Auburn Hills, Michigan, USA. Chrysler was first organized as the Chrysler Corporation in 1925....
and US Royal
United States Rubber Company
The United States Rubber Company was founded in Naugatuck, Connecticut in 1892. It was one of the original 12 stocks in the Dow Jones Industrial Average, and became Uniroyal Inc...
offered run-flat tires using an interlining to carry the weight. Bridgestone run-flat tires are supplied on most new model BMW
BMW
Bayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
cars. BMW promoted these as a safety feature and as an alternative to carrying a spare tire.
Self-supporting run-flat tires are now 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 subject to this kind of misuse, they may become irreparably damaged in the process. In addition, if the tire is punctured in the sidewall or at the edge of the tread, repair may be impossible or unsafe. These tires typically carry a 15% - 27% weight penalty over similar standard tires, or additional 2–3 kg (4-7 lb). The additional mass concentrated on the outer edge of the wheels can impose a significant performance penalty due to greater rotational inertia and unsprung mass.
Self-sealing
These tires contain an extra lining within the tire that self-seals in the event of a small hole due to a nail or screwScrew
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...
. 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.
There are also a number of retrofitted tire sealant
Sealant
A sealant may be viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary reaction...
s which act in a similar way to self-sealing tires. These compounds are normally injected through the tire valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
. The rotating force then distributes the compound onto the inner surface of the tire to act as a self-sealing lining within the tire.
Auxiliary-supported
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. While these systems generally offer better ride quality because their sidewall's stiffness can be equivalent to a standard tire, the requirement to have both special wheels and special tires increases cost and limits these systems from widespread use.Performance characteristics
Depending on the design, some run-flat tires perform better than regular tires, and some slightly worse. Some run-flat tires have a 20% higher rolling resistanceRolling resistance
Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or tire rolls on a flat surface, in steady velocity straight line motion. It is caused mainly by the deformation of the object, the deformation of the surface, or...
, in part due to their added structural material and mass. On the other hand, internal bracing in some run-flat tires reduces deformation, with the opposite effects of reducing rolling resistance and improving fuel efficiency.
Further advantages are derived from not needing to carry a spare wheel: The space can be used for other purposes. Also, the absence of a spare wheel contributes to lower vehicle weight which will in turn reduce fuel consumption, reduce harmful exhaust emissions, improve performance, handling and braking characteristics. However, these may be negated by the increased weight of the tires if they are self-supporting.
Due to reinforcement in tire side walls, run-flat tires usually give firmer rides compared to conventional tires.
Standards of Performance
The primary benefit of using run-flat tires is continued mobility in case of a loss of air pressure, either due to a 'normal' puncture or a hostile deliberate act or even a bullet shot while the vehicle is travelling at high speed. Performance criteria are therefore in terms of distance and speed at which the vehicle can escape without becoming immobile and the steering control over the vehicle during this process.
The usual standard of performance, especially for military or security vehicles, are the Finabel
Finabel
Finabel is a European organisation created with a view to promote interoperability and cooperation between the national armies of the member states of the European Union . The organisation was founded in 1953, and its name is the acronym of the initial letters of the member states - France, Italy,...
standards.
Market share
Run-flat tires accounted for less than 1% of replacement tire sales in the U.S. in 2005. In 2006, it was expected that such tires would gain popularity with armored vehicle manufacturers, but growth figures were slow with one major model, the Michelin PAX, being discontinued by the manufacturer. A Michelin study released in 2008 found that only 3 percent of drivers worldwide want run-flat tires. U.S. market share is well below 1 percent. American Honda Motor Co. announced that the 2009 Honda Odyssey Touring and Acura RL were its last models available with run-flat tires and with Honda no longer using run-flats. This leaves only a handful of volume manufacturers offering them as standard fittings and only on some models. An exception is BMW, who are the largest fitter of run-flats as original equipment.See also
- TweelTweelThe Tweel is an experimental tire design developed by the French tire company Michelin. The tire uses no air, and therefore cannot burst or become flat...
- Michelin's air-free tire - Tire manufacturingTire manufacturingPneumatic tires are manufactured according to relatively standardized processes and machinery, in around 450 tire factories in the world. With over 1 billion tires manufactured worldwide annually, the tire industry is the major consumer of natural rubber...
- Tire-pressure monitoring system
- Direct TPMSDirect TPMSDirect TPMS, or direct tire pressure monitoring systems refers to the use of a pressure sensor directly mounted on the wheels or tires of a vehicle. The pressure inside the tire is measured using a pressure transducer with the pressure information being subsequently sent to the vehicle to warn the...
- Tire mousseTire mousseTire mousse is a component in certain types of off-road run flat tires, designed to allow them to maintain functionality despite a puncture. It is a ring of flexible foam that is placed inside a tire before it is fitted on the rim. The original run-flat mousse, called Bib-Mousse, was developed in...