Driven: Smoother, quieter new Bridgestone third generation runflat tire

In central Italy, modern Mini Coopers are mid-size and pizza is supposed to come with crispy, even slightly charred, crust. It is here that the Bridgestone tire company opened a state-of-the-art, 346-acre proving ground in 2004. The Japanese company claims that it chose this location near Aprilia, south of Rome, because the weather is relatively regular and consistent. After spending a few days in Italy under Bridgestone’s care, though, I suspect that the location was selected at least partially because central Italy--with its natural beauty, beautiful people, hearty cuisine, and rich wines--closely resembles paradise.

Granted, the region also can be hell on tires, thanks to Rome’s ancient cobblestone lanes and agricultural Italy’s sometimes pockmarked back roads. Roads like these bring out the worst in runflat tires, which are often justifiably panned for their harsh ride characteristics. (The harshness is mostly a result of runflats’ superstiff sidewalls, which allow the tires’ eponymous ability to operate for a brief time without air but diminish the rubber’s, uh, rubberiness.)

Bridgestone’s new third-generation runflat tire (which the company refers to as 3G RFT), however, has significantly advanced the company’s line of runflats. Whereas the second generation was merely tolerable compared with the suppleness of a conventional tire, the third generation’s variations are almost undetectable from behind the wheel. I can say that confidently, too, because I drove almost identical BMW 5-series vehicles fitted with conventional Bridgestone RE050 tires, second-generation runflats, and 3G RFTs back-to-back-to-back on short sections of the Aprilia test facility. In addition to the new tire’s drastically improved ride, it also transmits slightly less road noise into the cabin of the car.

Bridgestone claims that the 3G RFT’s sidewall is only about 105 percent stiffer vertically than that of a conventional tire, versus the 115 percent stiffer second-generation. A new “NanoPro-Tech” rubber polymer and a new deformation-reducing ply help manage heat in no-air situations; therefore, less sidewall rubber is required to permit the tire to safely travel up to 50 miles at 50 mph, an unchanged target.

Perhaps most importantly, the 3G’s behavior is so similar to that of conventional tires that Bridgestone is willing to recommend this tire as an aftermarket replacement for vehicles that originally came with traditional tires--and have tire-pressure monitoring systems, which were made mandatory in the United States beginning for the 2008 model year. In the past, the company’s runflats have been installed only on vehicles whose suspensions were specifically engineered by their makers to minimize the effects of the shoes’ stiff sidewalls and additional weight.

Bridgestone will also produce an increased number of sizes in the 3G RFT lineup, particularly tires with taller (and necessarily thicker) sidewalls, which will be supplemented by distinctive, paddlelike “cooling fins” designed to create turbulence.

The 3G RFT is already in production in Japan and is set to debut later this year on an unidentified BMW, most likely the 5-series Gran Turismo and/or the X5 M and X6 M SUVs. Bridgestone currently supplies original-equipment runflat tires to Aston Martin, Audi, BMW, Ford, Lexus, Maserati, Nissan, and Toyota. The company developed its first runflat tire for the 1987 Porsche 959. After twenty-two years, though, runflats comprise only one or two percent of the U.S. and Canadian markets; thanks in part to its new third-generation runflat technology, Bridgestone expects that figure to increase to ten percent by 2019.

If runflat tires weren't so darn pricey, I bet even more people would get rid of their spare tires ...

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