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Run-Flat tires


The new Bridgestone DriveGuard, unveiled earlier this year, has finally attracted the attention of the public on run-flat tires

Paolo Ferrini


With its new DriveGuard, unveiled earlier this year, Bridgestone has placed run-flat tires under the spotlight once again, after having been culpably neglected by the industry’s manufacturers and car makers alike for quite some time. And consequently also by the average motorists.

Overwhelmed by a flurry of more or less useful electronic devices and systems, designed to make our driving experience safer and more comfortable, the important contribution that run-flat tires can make towards the same has been overlooked by the majority. Sure, they are definitely less attractive than most electronic devices, but imagine having a puncture at night or, even worse, under a heavy downpour, that is when you will really appreciate the possibility of reaching, albeit at a reduced speed, the nearest tire fitter or at least get to a safer place where changing tires becomes “easier and more comfortable”.


Why so little success?                                                 

Why then so little success? It is a fact that run-flats have, so far, not received the unconditional approval they actually deserved by car manufacturers (and consequently the public), and for many reasons. For one thing, in recent years there hasn’t been a single homogeneous proposal by the producers.

Two options have been proposed so far: the first being an essentially mechanical solution that involves inserting special parts between the tire and the rim or a specific wheel/tire match; the second involves self-supporting tires, using new compounds and structures. The result? This has led to a number of very different proposals that, despite being singularly convincing, have probably disoriented the public as well as car makers who, by adopting them as OE on their best selling models, could have kick-started the production levels to reach the necessary volumes and create an adequate aftermarket as well.

Furthermore, to make things worse, total confusion was created through poor communication. Some recommended not to exceed certain speeds and distances after a puncture, while others provided different data. In addition, some argued that punctured run-flats had to be removed, eliminated and replaced, others argued that they were easily repairable and fully reusable. In short, a chaotic situation, a difficult knot for anyone to unravel.


The contribution of technology           

Meanwhile, technology has moved on with great strides, especially in the field of self-supporting tires with new compounds and structures without having to rely on special parts inserted between the tire and the rim or imposing a specific tire/wheel match.

This is the path that Bridgestone has taken, developing its new DriveGuard run-flat, one that looks at breaking the mould of a tire made for a specific vehicle, going from niche to mass production, becoming a valid alternative to Bridgestone’s Turanza T001, for example, with a slight – and this is the first technological breakthrough - 5% weight increase, but still able to guarantee an A for wet grip, the highest possible, and a flawless driving line even if completely deflated, without transmitting any vibrations to the steering wheel. New Nanoprotech compounds, special reinforcements on the sidewalls and new solutions such as Cooling fins on the shoulders are only the latest steps of the technological evolution of the run-flat whose roots date back to about 80 years ago.


And now a bit of history

Due to the roughness of the roads back in the first half of the nineteenth century, getting a puncture was a pretty likely event and therefore a very sensitive issue for all motorists. That is why more than 80 years ago, precisely in 1934, Goodyear introduced its Lifeguard Safety Tube equipped with a second air chamber in fabric, which released air slowly inside the Tire. Twenty years later, in 1955, the Akron based company unveiled Captive-Air, a tire with a steel-cord safety shield that acted as an inner-spare, and in 1963 it was the turn of the Double Eagle with the Lifeguard Safety Spare reserved for some luxury models, something like a tire with a “built-in spare”. They were all forerunners of today's run-flats.

On this side of the Atlantic the first "anti-puncture tires" appeared only at the beginning of the seventies. After launching, in February 1972, its “Total Mobility tire” Series 60 radial tubeless, capable of not coming off the rim in the event of a puncture or even a blowout, in 1973 Dunlop presented the first version of its Denovo. After reinforcing the bead, a special design ensured a perfect seal whether the tire was inflated or not, allowing the driver to carry on driving even with a flat tire being supported by a double layer of rubber: the tread and the specially designed bead, which could not come off the rim. A special lubricant allowed the two rubbers to slide within each other without creating an excessive friction.

This non-toxic liquid could be used at any temperature, preserving its characteristics unchanged for an indefinite time, automatically sealing small punctures, and the heat developed through the rolling resistance increased the internal pressure between 0.2-0.3 PSI.

The first run-on-flat tire, capable of supporting the load of the vehicle even after an air pressure loss, made his appearance at the 1978 New York Motor Show, where Goodyear introduced its SST. But production difficulties and the high costs of the necessary devices to signal pressure drops undermined its commercial success.

The 90’s on the other hand can rightly be considered the turning point in the history of run-flat tires. Starting in 1987, Bridgestone entered this sector with its first RFT (Run Flat Technology) - the Potenza RE71 – designed for the Porsche 959 and two years later, in 1992, Goodyear announced the development of its Eagle GS-C EMT (Extended Mobility Technology), a run-flat tire suitable for conventional wheels of all kinds. Offered on demand on the Chevrolet Corvette in 1994, it was the first case of a run-flat approved as original equipment. In 2004, Dunlop, following its merger with Goodyear, also adopted EMT technology, offering it to the public as DSST (Dunlop Self Supporting Technology).

In the meantime, in 1998, Michelin had already decided to follow a path of its own. The Michelin PAX System involved the use of a semi-rigid ring installed onto the rim using special equipment. This insert, provides support to the tire and its sidewall allowing emergency operations at limited speed until such time when the tire can be replaced.

Continental too, thanks to a collaboration with Bridgestone and Yokohama, developed, in 2001, its Conti Support Ring (CSR), a light stainless steel ring with flexible support mounted on a standard wheel, preventing the tire from rubbing against the rim in case of a puncture.

In 2010, Yokohama too decided to enter this segment of the market with its own run-flat, the Self Supporting Run Flat Tire - ZPS (Zero Pressure System). Unique sidewall reinforcements, supportive bead fillers and durable bead wire support the weight of the vehicle in the event of complete loss of air pressure. This technology, designed specifically for ultra-low profiles, was designed to ensure a comfortable and quiet ride despite the increased stiffness of the tire structure.



A few figures on tire punctures

60% of motorists experienced a tire puncture over the last four years

23% of the cases happened after dark or in awkward places

72% of women drivers do not change a flat tires

Over 50% do not trust the donut wheel or know how to use it properly

A motorist out of three does not know how to properly use a Mobility Kit

93% of motorists lost more than 3 hours in managing a puncture

Over 25% of motorists have children on board




From Milan to Rome Toll-to-Toll with 4 flat tires!

To clarify beyond any doubt the great potential of run-flat tires, on April 30, 2003 Goodyear organized a spectacular test on the Monza race track, in the presence of a notary, a few timekeepers from the Italian federation as well as CSAI commissioners to certify the results. For the occasion a Mini Cooper, equipped with four completely flat 195/55 R16 TL 87V Goodyear Eagle NCT 5, ran 92 laps, totaling 532.9 km (like going from Milan to Rome Toll-to-Toll), without ruining the four tires and above all without jeopardizing the safety of the driver.

At the same time, a second Mini Cooper made 13 laps (equivalent to 75.3 km) with the two front tires completely flat without exceed 80 km/h and 13 more laps with four repaired tires at free speed (exceeding 165 km/h). This second trial confirmed that Goodyear EMT run-flat tires, not only can be repaired with normal garage equipment, but also safely reused after running with no internal air pressure the mileage limit specified by the manufacturer. After eight hours of continuous testing and after repairing the two front right tires five times with normal garage equipment, 532.9 km were driven without any particular problem to the tires.

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