![Aufgeschnittener Piranha-Pneu](https://upload.wikimedia.org/wikipedia/commons/a/a8/Aufgeschnittener_Piranha-Pneu.jpg)
A run-flat tire/tyre is a
pneumatic vehicle
A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), ...
tire
A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...
that is designed to resist the effects of deflation when punctured, and to allow the vehicle to continue to be driven at reduced speeds - under – and for limited distances – usually , depending on the type of tire.
Technologies
There are three basic technologies currently available, described below.
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
blowouts, a common and dangerous occurrence in the 1930s.
In 1934,
Michelin
Michelin (; ; full name: ) is a French multinational tyre manufacturing company based in Clermont-Ferrand in the Auvergne-Rhône-Alpes ''région'' of France. It is the second largest tyre manufacturer in the world behind Bridgestone and la ...
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-bulletproof". While the tire performed as advertised it was far too expensive to be a feasible option for most private automobile users.
In 1958,
Chrysler
Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automoti ...
teamed with
Goodyear Tire and Rubber Company
The Goodyear Tire & Rubber Company is an American multinational tire manufacturing company founded in 1898 by Frank Seiberling and based in Akron, Ohio. Goodyear manufactures tires for automobiles, commercial trucks, light trucks, motorcycles, S ...
to offer Captive Air run-flat tires using an interlining to carry the weight.
In 1972
Dunlop launched the Total Mobility Tyre (later Denovo) "fail-safe" wheel and tire system that became optional equipment on the
Rover P6
The Rover P6 series (named as the 2000, 2200, or 3500, depending on engine displacement) was a saloon car produced by Rover and subsequently British Leyland from 1963 to 1977 in Solihull, Warwickshire, England, UK.
The P6 was the first winner ...
3500 in 1973, and by 1983 evolved into the TD/Denloc which became standard equipment across the whole
Austin Metro
The Metro is a supermini car, later a city car that was produced by British Leyland (BL) and, later, the Rover Group from 1980 to 1998. It was launched in 1980 as the Austin mini Metro. It was intended to complement and eventually replace the ...
range.
Most recently,
Bridgestone and
Pirelli run-flat tires are supplied on some new model
BMW cars. The automaker promoted these as a safety feature and as an alternative to carrying a spare tire.
![Cut-Out View of PZT](https://upload.wikimedia.org/wikipedia/commons/f/f5/Cut-Out_View_of_PZT.jpg)
Pressure Zero Tire (PZT) was pioneered by American Engineering Group (AEG) for US Special Forces. AEG prototype dissipates heat and has the tire flexibility and strength to support the heavy military pick-up weight while providing a relatively smooth ride. The durability characteristics of this design were studied further on four different tire sizes for ATV Polaris, Toyota Hilux, and Toyota Land Cruiser & GMV 1.1. special operations vehicles.
Self-supporting run-flat tires are now common on light trucks and passenger cars and typically allows the vehicle to be driven for at around . However, if the tires are subject to this kind of misuse, wheels may become damaged in the process, and repair may be impossible or unsafe, especially if the tire is punctured in the sidewall or at the edge of the tread. These tires carry a 20% to 40% weight penalty over similar standard tires and the thicker sidewall also means higher rolling resistance, which reduces the vehicle's fuel economy.
However, the weight penalty of the individual tire is usually more than compensated by the fact that the vehicle need no longer carry a spare, as well as the equipment needed to swap in the spare. The thicker sidewall however results in more road imperfections filtering through the tire to the rim and hence to the car, which results in a harsher ride.
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
Nail or Nails may refer to:
In biology
* Nail (anatomy), toughened protective protein-keratin (known as alpha-keratin, also found in hair) at the end of an animal digit, such as fingernail
* Nail (beak), a plate of hard horny tissue at the tip ...
or
screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
. 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
retrofit
Retrofitting is the addition of new technology or features to older systems. Retrofits can happen for a number of reasons, for example with big capital expenditures like naval vessels, military equipment or manufacturing plants, businesses or go ...
ted tire
sealant
Sealant is a substance used to block the passage of fluids through openings in materials, a type of mechanical seal. In building construction ''sealant'' is sometimes synonymous with ''caulking'' and also serve the purposes of blocking dust, s ...
s which act in a similar way to self-sealing tires. These compounds are normally injected through the tire
valve
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...
. 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
![Sicherheitsreifen BMK](https://upload.wikimedia.org/wikipedia/commons/0/0f/Sicherheitsreifen_BMK.jpg)
In this system, there is an additional support ring or insert attached to the wheel that can support the weight of the vehicle in the event of a loss of pressure. The run-flat insert has an unsurpassed ability to carry heavy vehicle loads for long distances at high speeds. It is therefore the normal run-flat selection for military vehicles, high-level executive protection vehicles, and "
armored
Armour (British English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat, or f ...
" vehicles
[Test Operations Procedure (TOP) 02-2-698 Runflat Testing](_blank)
.-U.S. Army Test and Evaluation Command. - 2015. used by government, aid groups, or private contractors in conflict zones.
Standards of performance
The basic benefit of using run-flat tires is continued mobility in case of a loss of air pressure, due either to a 'normal' puncture or to a hostile deliberate act including a bullet strike while the vehicle is traveling 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 is a European organisation for the promotion of cooperation and interoperability between the national armies of the member states of the European Union (EU). Founded in 1953, Finabel is controlled by the chiefs of staff of its member st ...
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 System
The Michelin PAX is an automobile run-flat tire system that utilizes a special type of rim and tire to allow temporary use of a wheel if its tire is punctured. The core of Michelin's PAX system is the semi-rigid ring installed onto the rim using sp ...
, no longer being developed by the manufacturer (though replacements will be produced for the foreseeable future). A Michelin study released in 2008 found that 3% of drivers worldwide want run-flat tires. U.S. market share is well below 1%. 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.
Former US President Barack Obama's presidential limo, "
the Beast", had Goodyear Kevlar lined run-flat tires.
Factors contributing to small market share
The cost can be more than double other tires of comparable size. Also, run-flat tires cannot be run flat if the flat is due to sidewall damage, a common cause of flats. Also, under the best circumstances, the speed and range that the run-flat tires can be run flat is very limited. Run-flat tires cannot be driven over 50 miles per hour and usually offer only up to 50 miles of extended mobility. These limitations lower the value of the extra expense for many buyers. In certain applications, depending on the vehicle, specific tire design, and driving surface, a run-flat tire can provide from 25 miles to 200 miles driving while flat with limited speed.
For Goodyear Tire, one effect on market share is the policy to prohibit the repair of tires punctured by nails or other road hazards; while Goodyear tires can be repaired, the manufacturer's warranty and liability is voided.
See also
*
Airless tire
*
Direct TPMS
Direct TPMS, or direct tire pressure monitoring systems (direct sensor TPMS) refers to the use of a pressure sensor directly mounted on the wheels or tires of a vehicle.Hawes, p. 1. The pressure inside the tire is measured using a pressure transd ...
*
Tire manufacturing
Pneumatic tires are manufactured according to relatively standardized processes and machinery, in around 455 tire factories in the world. With over 1 billion tires manufactured worldwide annually, the tire industry is a major consumer of natura ...
*
Tire mousse Tire 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.[Tire-pressure monitoring system
A tire-pressure monitoring system (TPMS) monitors the air pressure inside the pneumatic tires on vehicles.
A TPMS reports real-time tire-pressure information to the driver, using either a gauge, a pictogram display, or a simple low-pressure wa ...]
*
Tweel
The Tweel (a portmanteau of ''tire'' and ''wheel'') is an airless tire design developed by the French tire company Michelin. Its significant advantage over pneumatic tires is that the Tweel does not use a bladder full of compressed air, and th ...
- Michelin's air-free tire
References
{{DEFAULTSORT:Run Flat Tire
Tires
Vehicle technology
it:Pneumatico tubeless#Evoluzioni