Run Flat - what are the tyres and is it worth investing in?

  • Author: OPONEO.CO.UK

It is worthwhile to read the tips on how to use Run Flat tyres. Otherwise, Run Flat tyres can do more harm than good. Read why it is worth using this technology.

A tyre explosion at a high speed is very dangerous.

Run flat tyre - what is it?

The history of Run Flat tyres began already before World War II. The dynamic development of this technology took place during the war, and further work was carried out after the war. On a wider scale, this solution has been used in passenger cars since the late 1980s.

Run Flat tyres are currently gaining in popularity. Most RunOnFlat tyres allow you to drive 50 miles after a puncture at around 50 mph (although there are other options). They are manufactured on the basis of three main technological solutions, described later in this article.

Is it worth buying Run Flat tyres?

When you're thinking about buying Run Flat tyres, it's a good idea to look at the advantages and disadvantages of these tyres.

 

Advantages

          Disadvantages               

safety (no risk of losing control of the vehicle after a sudden puncture)

higher price and weight of the tyre

no need to replace the wheel immediately (e.g. in a hazardous area)

poorer comfort (more noise and worse damping of unevenness)

more space in the boot (no spare wheel)

more rigid tyres wear out faster

greater resistance to mechanical damage (e.g. when driving into a hole or hitting a kerb)

can't be fixed in every vulcanization service.

protection against theft of a car on the wheel - if someone tries to stop a car with Run Flat tyres by signalling an alleged puncture, the driver knows that it is an attempt to steal the car

some models cannot be repaired - after puncture they are suitable for replacement

 

occurrence of false tyre pressure sensor readings

 

The table shows that Run Flat tyres have more disadvantages than advantages. However, these are only appearances. Definitely, the disadvantages of this solution are higher operating costs (price, faster wear and tear, more difficult installation). The main advantage, however, is that the risk of a tyre being blown out after a puncture is practically zero, which means a high level of safety. At this point, it is worth asking yourself: does the safety of the driver and his passengers have a price?

Run Flat tyres are fitted on high performance luxury cars. Owners of such cars often travel longer distances, on highways and expressways. It's not hard to imagine what would happen if ordinary tyres were punctured and you lost control of your car at speeds like 80 mph - and still only very few drivers know how to react to a tyre burst while driving.

A puncture in a Flat Run tyre is hard to spot, and the fastest way to detect it is through the wheel pressure control system.
 

 

What's the Run Flat tyre pressure?

You will find all the necessary tips for the proper use of a car with Run Flat tyres in its owner's manual. For example, it is permissible to inflate such tyres with nitrogen, but not all manufacturers allow the use of products designed to seal small punctures. As with standard tyres, the best possible solution is to maintain the pressure at the level recommended by the manufacturer.

 

Principles of use of Run Flat tyres

1 The car on which the Flat Run tyres are fitted must have functional wheel air pressure sensors. Without them, we will not know that there is a problem.

2. Cars with Run Flat tyres should be specially adapted to them. In this case, suspension components (e.g. BMW with softer suspension settings) and power steering systems (ABS, stability systems) are designed and calibrated to work exclusively with this type of tyre. Fitting ordinary Run Flat tyres will result in unpredictable performance at high speed.

3. Run Flat tyres should only be fitted by professional tyre repair shops. Fitting them on a common mount usually results in damage to the side or bead of the tyre. This can result in an unexpected blowout at high speed, which in turn can result in a serious accident.

4. It is assumed that Run Flat tyres can cover a distance of approximately 50 miles (80 kilometers) after a puncture at a speed not exceeding 50 mph (80 km/h). It is worth remembering that these are average values. It is not always possible to take advantage of the full potential of this technology.

5. Run Flat tyre manufacturers advise against exceeding the maximum reach of these products. In exceptional circumstances, however, they can withstand much more. At low ambient temperatures, when the speed is reduced to 50 km/h, the range of these tyres can increase by at least 50% compared to " standard " conditions.

6. Some manufacturers allow repair of punctured Run Flats. Please note, however, that the range of the tyre will be reduced by several kilometers when the next damage occurs.

7. If the pressure drops, inflate the damaged tyre as soon as possible, e.g. at the nearest petrol station. The pressure after a puncture usually drops slowly. Inflating the wheel will reduce the risk of permanent damage to the tyre.

 

Bridgestone's Run Flat tyres have been used in some BMW models.

 

Symptoms of a Run Flat puncture

  • alarm from the wheel pressure sensors,

  • an increase in the force required to turn the steering wheel (in the event of damage to the front wheel),

  • slightly pulling the car over to the damaged tyre side,

  • increase in noise level while driving,

  • vibrations or the sensation of wheel banging at speeds above 90-100 km/h.

Run Flat winter tyres

Many drivers are wondering if the winter Run Flat models are suitable for this demanding season. Research shows that they are as well adapted to winter conditions as conventional seasonal tyres. They use the same technology as their standard counterparts. The only drawback is that winter runflat tyres have a slightly harder structure that can affect driving comfort. However, safety parameters generally remain unchanged.

Attention!: It is very harmful for Run Flat tyres to increase the temperature when driving without air after a puncture. The worst conditions are driving in the heat on a punctured road with a heavy load (e.g. a family holiday).

Technologies used in Run Flat tyres

Run Flat tyres are generally divided into three types: reinforced, self-sealing and with  a support ring.

 

Technology

Description

Examples

Reinforced construction

There is a rubber insert in the sidewall of the tyre to help absorb pressure loss. The tyre bead, which is firmly attached to the rim, is also reinforced. The solutions used make the sudden loss of pressure almost imperceptible for the driver. Hence the need to use pressure sensors.

  • Goodyear ROF (RunOnFlat)

  • Continental SSR (Self Supporting Runflat)

  • Bridgestone RFT (Run Flat Tire)

  • Dunlop ROF

  • Firestone RFT (Run Flat Tire)

  • Dunlop DSST (Dunlop Self-Supporting Technology)

  • Michelin ZP (Zero Pressure)

  • Goodyear EMT (Extended Mobility Technology)

  • Yokohama Run Flat

  • Pirelli SSRF (Self-Supporting Run Flat, Run Fla Technology)

  • Kumho XRP

Self-sealing

Tyres have an additional sealing layer inside. In the event of a puncture, this sealing layer helps to stabilize the correct pressure level. These tyres are considerably heavier than the standard tyres (15 to 20 percent) and there have also been problems with balancing the wheels. Therefore, this technology has not found a wider scope for use.

  • Goodyear Dureseal (for trucks)

  • Continental ContiSeal

  • Kleber Protectis

  • Pirelli SWS (Safety Wheel System)

Support ring

This is a technology that involves the use of a special ring in the interior of the tyre. In the event of  pressure loss, the ring acts as a carrier and additionally prevents the tyre from slipping off the rim.

  • Michelin PAX,

  • Bridgestone Support Ring (BSR),

  • ContiSupportRing.

The individual technologies are described in detail below:

 

DSST – Dunlop Self-Supporting Technology

  • In use since 1998.

  • In the event of a drop in air pressure, the weight of the vehicle is transferred to the patented structure of the reinforced sidewalls of the tyre.

  • Acceleration, braking and steering are virtually unchanged when driving without air.

  • DSST tyres are suitable for mounting on standard rims after the vehicle has been fitted with an air pressure warning system (Dunlop Warnair recommended).

  • Range up to 80 km/h at speeds up to 80 km/h.

 

EMT - Goodyear Extended Mobility Tyre

  • It's been in business since 1992.

  • In the event of a drop in air pressure, the vehicle's weight is transferred to the reinforced tyre sidewalls.

  • The vehicle shall be fitted with a Tyre Pressure Monitoring System (TPMS).

  • The EMT series is only recommended for vehicles whose manufacturer has approved the EMT series as a standard or optional extra.

  • EMT tyres may be repaired in accordance with the specified conditions. However, provided that the damage has occurred on the tread surface and not on the sidewalls.

  • Range up to 80km at up to 80km/h (except for the extended Chevrolet Corvette).

 

HRFS - Hankook RunFlat System

  • Technology introduced in 2004.

  • The system is based on stiffened inserts on the sides of the tyres.

  • HRFS tyre selection is limited to the most expensive luxury, sports and SUV cars.

  • Range up to 80 km at speeds up to 80 km/h.

 

PAX – Michelin

  • The solution has been in use since 1999.

  • The support is a lightweight plastic insert on the rim, placed inside the tyre, carrying the full load in the event of a lack of pressure. A special bead construction prevents the tyre from separating from the rim while driving.

  • A complete wheel with a PAX system tyre weighs on average 17 % more than a standard wheel with a tyre of the same size. The total weight of the PAX wheel set is less than five standard wheels (four plus spare).

  • Compared to tyres with stiffened sidewalls, PAX series tyres maintain full suspension comfort under normal driving conditions and therefore do not burden the suspension and wheel rims with additional work. However, the driving characteristics are worse when driving without air.

  • PAX tyres require dedicated rims.

  • PAX provides a range of up to 200 km at speeds of up to 88 km/h.

  • The first cars equipped with PAX system as standard on the European market were Renault Scenic (since February 2002), Audi A8 (since December 2002), Rolls-Royce Phantom (since January 2003) and Audi A4 (since September 2004).

  • The PAX system is very expensive and Michelin no longer uses it, but cars with PAX tyres can be found in the aftermarket.

 

RFT – Bridgestone Run Flat Tyre

  • Technology used since 1987

  • The basis is the reinforced sidewalls of the tyre.

  • The first generation of RFTs includes tyres manufactured between 1987 and 2004. The most important feature of the second generation (since 2005) is the improved sidewall construction for better comfort in the selection of unevenness. The third generation (since 2009) also has improved side wall cooling. If the temperature increase rate after the pressure drop in the first generation of RFT tyres is assumed to be 100%, it has fallen to 85% in the second generation and to only 42% in the third generation. The comfort of unevenness selection is also improved. If the stiffness of a conventional tyre is assumed to be 100%, it would reach 120% in RFT I, 115% in RFT II and 105% in RFT III.

  • Bridgestone recommends that EH2 type rims be used in conjunction with RFT tyres, although they may also be fitted on standard rims.

  • An RFT emergency repair is permitted in the event of a puncture on the tread surface, but should be replaced as soon as possible.

  • A car with RFT tyres should be fitted with a Tyre Pressure Monitoring System (TPMS).

  • Maximum range up to 80 km at a speed up to 80 km/h.

 

RSC – BMW Runflat System Component

  • In use since 1999.

  • It's not just a tyre, it's a complete system for unpressurised driving: it consists of tyres with reinforced sides (e.g. Michelin ZP), an EH2 rim that prevents the tyre from separating from the bead when there is no pressure and an air pressure monitoring system.

  • Maximum range up to 150 km at a speed of up to 80 km/h.

 

SSRF – Pirelli Self-Supporting Run Flat

  • Pirelli developed its research program in collaboration with the Goodyear team.

  • The SSRF system is based on the reinforced sidewalls of the tyres.

  • It is recommended to mount SSRF tyres on EH2 rims, however standard rims are allowed. The car must be fitted with an air pressure monitoring system (TPMS).

  • The repeatability of SSRF tyres is ensured by the MIRS™ robot control computer system, which makes it easier to optimise the production process.

  • The company's debut on the market of airless tyres was the 17-inch Scorpion BK designed specifically for the off-road luxury Lamborghini LM-002, manufactured since 1986.

  • A punctured SSRF tyre should be replaced with a new one.

  • Maximum range up to 80 km/h at a speed up to 80 km/h.

 

SSR – Continental Self-Supporting Runflat

  • Uses reinforced tyre sidewalls.

  • SSR tyres are suitable for most standard rims. However, the vehicle must be equipped with an air pressure monitoring system with sensors attached to the rims.

  • SSR tyres are not suitable for repair after airless driving.

  • Maximum range up to 80 km at a speed of up to 80 km/h.

 

Run Flat tyres in their interior have special reinforcements, which allow you to drive without air (photo: Continental).

TRF – Toyo Run Flat

  • Rigid inserts on the tyre sidewalls transfer the load in the event of a drop in air pressure.

  • The special bead construction prevents the tyre from slipping off the rim.

  • The additional layer of cord on the sides is heat-resistant.

  • The TRF is always accompanied by the tyre pressure index.

  • Range up to 80 km at a speed of up to 88 km/h.

 

XRP – Kumho eXtended Run-Flat Performance

  • The solution has been in operation since April 2006.

  • Unique bead design prevents the tyre from slipping off the rim.

  • The special rubber compound has increased heat resistance.

  • XRP tyres can be used on any passenger car.

  • Air pressure and temperature sensors are mounted on wheel rims.

  • Range up to 80 km at a speed of up to 80 km/h.

 

ZP – Michelin Zero Pressure

  • A solution used since 1995.

  • When the air pressure drops, the tyre rests on its stiffened sidewalls.

  • ZP tyres may only be used in cars that have been designed to work with run-flat tyres and are fitted with rims dedicated to ZP. The ZP series includes Michelin Primacy HP, Pilot Sport and Pilot Alpin.

  • If more than one tyre is damaged, it is recommended that the journey be interrupted.

  • As a general rule, tyre repair after a flat tyre is not permitted.

  • Range up to 80 km at a speed of up to 80 km/h. With tyres additionally marked "SR", the range is extended to 112 km (70 miles).

 

ZPS – Yokohama Zero Pressure System

  • A relatively new solution has been available since 2009 in the ADVAN Sport model.

  • The system uses stiffened sidewalls made of composite material to limit the temperature increase.

  • A special filler layer between the stiffener and the bead increases the comfort of driving under normal conditions and the certainty that the tyre is seated on the rim when driving without pressure.

  • The hexagonal cross-sectional shape of the wire rod prevents the bead from slipping off the rim.

  • Air pressure sensors ("G Sensor" Vehicle Behaviour Detection System) in wheels.

  • Range up to 80 km at a speed of up to 80 km/h.

 

View our range of Run Flat Tyres

 

Run Flat Technology has a very long history.

 

History of Run Flat  tyre

Pre-war beginnings

1934 - Goodyear introduces LifeGuard technology to the market. An additional nylon inner tube was in the middle of a normal inner tube. In the event of a blowout or puncture, the tyre could briefly take over the entire load. The system prevented sudden air pressure drops, often resulting in an accident, but couldn't get far. The extra inner tube gradually released air, giving only enough time to find a safe place to replace the wheel.

War is the motor of progress

1941 - The U.S. Department of Defense announces a competition for U.S. manufacturers to develop a tyre that is capable of continuing to run after being blown out for at least 75 miles (120 km). Previous French and German solutions - models filled with rubber foam - did well in times of battle, with little driving and a lot of shooting. Unfortunately, they could be thrown away after a few dozen or so hundreds of kilometres of regular operation. The idea of tyres with reinforced sidewalls from Great Britain, on the other hand, allowed to cover even 50 miles (80 km) without air.

December 1941 - The final of the competition takes place on the road connecting Miami and Tampa (Florida) "Tamiami Trial", which runs through the Everglades marshes. The test results are poor. The best tyre only lasted 22 miles (35 km). However, the designers' work has not been wasted. By testing new materials for sidewall reinforcement, by the end of the war the Americans had managed to achieve a maximum airless mileage of 150 miles (240 km) in military tyres, where the production costs of the model were not a major factor. General Patton owed part of his rapid march from France to Germany to the innovative tyres in many modern military vehicles.

Dynamic development

1955 - Goodyear introduces a tyre with a Captive Air Shield made of plastic to support the load in the event of a loss of air pressure. It offers a safe range of up to 160 km at speeds of up to 80 km/h. Double Eagle models with optional LifeGuard Safety Spare inserts are advertised as "fitted with a built-in spare wheel" a few years later. Popularity is limited by the high price.

1958 - Chrysler offers tyres manufactured by US Royal that are capable of running short distances without air, with reinforced sidewalls.

1965  - NASCAR formula cars are fitted with Goodyear engineers' Lifeguard Racing Shield tyres. The system has been used successfully to this day.

October 1973 - The Austrian company Polyair (today a tycoon in the production of pneumatic cushions for trucks) presents a tyre with stiffened sidewalls made of an innovative type of polyurethane, which is flexible like rubber, but remains 4 times more resistant to wear. The Polyair proposal is 1/3 lighter than the traditional one, and thanks to the very high strength of the compound it is simpler to build, without layers of cord and warp. Produced by cheaper pressure casting method. It is capable of driving without air over a distance of up to 100 km at a speed of up to 70 km/h. The model heats up much more slowly and less than the tyre made of synthetic rubber, thanks to a significant reduction in the mid-molecular friction of the new compound. The initial disadvantage is poor grip on wet roads.
1978 - Goodyear introduces the SST (Self Supporting Tyre) tyre with a reinforced sidewall to carry the pressure drop load similar to what we use today. Permissible range: 40 miles (64 km) at up to 40mph (64 km/h).

Run Flat today

1987 - The Porsche 959 is the first car to be fitted with run flat tyres as standard (Bridgestone RE71). Since the mid-1980s, the brand's 175/70 R 13 run-flat tyres have been part of a package in Honda Civic that is accessible to people with disabilities. This allows you to travel up to 100 km at a speed of up to 60 km/h.

1997 - Goodyear Eagle F1 GS-EMT Run Flat Flat tyres are standard on the Chevrolet Corvette, providing a pressureless range of 320km at up to 88km/h at 22°C outside temperature.

April 1998 - Michelin presents the PAX system.

December 1999 - The Z8 Roadster is the first BMW to be fitted as standard with an RSC system (dedicated EH2 rims, Run Flat tyres and air pressure sensors).

 

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