Tuesday, July 7, 2009

Bridgestone 3rd Generation RFT

Here's the latest news regarding the infamous RFT ( Run Flat Tyres).
Bridgestone has announced their latest generation of RFT that promises to address the issue of harsh ride. Hopefully this new generation RFT delivers. Reading from the Autoblog review, it seems promising. The tyres perform as well as non RFTs.
Below are excerpts from autoblog:

Consumers embraced the additional mobility and safety benefits of the 2G RFT, but they never warmed to the handling compromises as a result of the additional unsprung weight, the harsh ride (the sidewalls are a noticeable 15 percent harder than a conventional tire, says Bridgestone), or the expensive replacement cost (up to 30 percent higher, in some cases). Frustrated, many vehicle owners exchanged their run-flat tires with conventional tires even before it was time for their replacement.

Meanwhile back in the laboratory, Bridgestone engineers were hard at work developing the third-generation run-flat (3G RFT, above) designed to address these concerns head-on. Their research and prowess resulted in three new cutting-edge technologies:

  • Unique ply construction: The reinforcing layers of a tire are called the "ply." Bridgestone developed a tire ply that uses the heat generated by a deflated tire to contract and curb deformation. In simple terms, the material in the new sidewalls automatically shrinks to abate damage from abrasion and heat. When the tire cools, the ply automatically returns to its original state.
  • New rubber compounds: Laboratory-engineered rubber compounds, Bridgestone calls them "NanoPro-Tech," are also used in the sidewalls to limit heat. Conventional tire compounds warm through friction between the carbon and polymers (two common tire ingredients). By optimally distributing the polymers, friction and heat are minimized. Of course, this also reduces energy loss increasing fuel economy.
  • Innovative heat control: Bridgestone developed so-called "cooling fin" technology for the new tire. Molded into the sidewall are small protrusions (think of them as miniature spoilers). While this seems rather rudimentary, they effectively disrupt the airflow at the surface to help radiate heat and cool the tire. Thermo-vision (heat sensing) photography of the "cooling fin" technology in action shows a dramatic improvement when compared to smooth sidewalls.

Bridgestone utilizes these technologies independently, or combined, based on the specific design parameters and size of each 3G RFT tire application. For example, the lower sidewalls of a sports car (e.g., BMW Z4) will unlikely receive cooling fin technology, but a higher-profile tire with more weight to bear (e.g., non-sport BMW X5) would have the cooling fins. Regardless of the formula, Bridgestone says all of its new 3G RFT tires are designed to operate safely with zero pressure for up to 80 kilometers (about 50 miles). But, more on that a bit later...

Leaving the technical jargon in the classroom, Bridgestone encouraged us to try its new third-generation run-flat (3G RFT) from behind the wheel. Lacking sensitive test equipment to capture objective differences between the 2G and 3G tires, we were understandably apprehensive approaching this tire "comparison." After all, how does one subjectively "feel" through fast-food sculpted posteriors the subtle nuances in ride quality that reportedly differentiate the two generations of run-flat tires? The answer was Bridgestone's European Proving Grounds in Italy.

The European Proving Ground (EUPG) is to a tire enthusiast what an unattended pharmacy cabinet would be to a drug addict – pure bliss. Located 50 km (about 30 miles) south of Rome, the purpose-built facility is a sprawling high-security testing ground for the latest in Bridgestone tire technology. Set within the outer perimeter gates of the four-year-old complex is a glass-smooth four-lane oval nearly 2.5-miles in length with 35-degree banking in each corner. Inside the oval, and connected for high-speed runs off the main track, is a massive skidpad (an amazing 22 acres of smooth concrete!), two independent short road courses, a wet handling course, and several side-by-side lengths of paved straight-aways designed to mimic various smooth and rough pavement surfaces found around the world. The whole package is wrapped in neatly manicured grounds sprawling with blooming Italian wildflowers.

Strapped in near identical late-model BMW 5 Series vehicles, Bridgestone offered us the opportunity to drive three different variants of its high-performance RE050A tire back-to-back: Conventional, 2G RFT, and 3G RFT.

We drove the conventional RE050A first. A high-performance tire fitted to such cars as the Nissan 370Z and Lexus IS-F, the standard rubber was comfortable on the smooth sections. The course/rough pavements didn't provide much of a challenge either as the compliant sidewalls absorbed the abuse without drama. We've put thousands of miles on these high-rated tires in the real world with few complaints.

Next, we tried a set of RE050A "2G" run-flats, the OEM application found on thousands of late-model BMW and MINI models. Owners appreciate the run-flat technology, but have raised issues with ride quality initiated by the stiff sidewalls and additional mass rotating on each wheel. While they were comfortable on the smooth sections, the compromises of the 2G run-flats were immediately evident when we entered the first sections of rough pavement. What had been damped by shock-absorbing sidewalls on the standard tires was now transferred into the cabin in the form of sharp, and rather uncomfortable, impacts. This test reinforced what many owners have expressed and what we have personally experienced.

The final run through the test course was done with the all-new RE050A "3G" run-flats. Eureka! Surprising even the skeptics among us, the third-generation tires were nearly imperceptible in ride quality from the standard tires (non run-flat) we had driven on merely minutes earlier. The ride was very comfortable. According to Bridgestone, test instruments reveal that the slight difference in ride quality was a near-imperceptible 5 percent change in harshness.

Bridgestone also allowed us to drive a 3G RFT technology-equipped vehicle with a flat tire through a simulated slalom course. The car handled sloppy, and the tire howled when pressed, but it was entirely controllable. Afterwards, the tire wasn't even very hot to the touch.

Driving their message even further, we were shuttled by bus out into the Italian countryside for some real-world observations. Another fleet of late-model BMW 5 Series vehicles were fitted with 2G RFT and 3G RFT tires for back-to-back comparisons. Bridgestone held us close (with pace cars front and rear) as we toured 2-lane roads across farms and into the surrounding hills. The roads were in fairly lousy condition, but they again demonstrated the newfound compliance one can expect with the third-generation run-flat.

While Bridgestone states that all of its new 3G RFT tires are designed to operate safely with zero pressure for up to 80 kilometers (about 50 miles), the reality is that a run-flat tire is designed to get you safely off the road and out of harm's way to where the tire may be safely serviced or replaced. In truth, a virtual clock starts ticking the moment a RFT loses pressure (the frictional stress and heat literally "cook" the service life out of the rubber compounds). Consequently, high vehicle loads, high ambient temperatures, and high speeds accelerate the clock, while light loads and cold temperatures slow it (when we experience a loss of pressure with a run-flat, we immediately pull over safely in the hope that the tire may be properly repaired before it is destroyed by driving on the vehicle). Of course, run-flat tires should never be fitted to a vehicle without a tire pressure monitoring system (TPMS).

The track sessions and test drives made it clear that Bridgestone has eliminated the biggest objection to run-flat tires – abusive ride quality. We never had an opportunity to push the performance envelope of the tire, but Bridgestone says the tread compound of the RE050A 3G RFT is identical to that on the conventional tire, so the grip levels should be very high. Lastly, the cost of RFT technology has come down a bit. While pricing has not been announced as of yet, Bridgestone expects the 3G RFT to carry a 20-percent price premium over the equivalent conventional tire, a small price to pay from a safety aspect.

Bridgestone's third-generation run-flat technology also seems to have clearly addressed the issue of comfort that plagued its predecessor. Moreover, the new "NanoPro-Tech" polymers and "Cooling Fin" technologies will undoubtedly allow the company to expand the fitments and marketability of the new 3G RFT product line, likely helping to bring the cost down even further.

While the first two iterations of zero-pressure tires from Bridgestone delivered the safety and mobility they promised, their negatives frequently outweighed the benefits... particularly in performance applications. Bridgestone's third-generation run-flat tires seem to represent a solution with far fewer compromises. It is a path we are finally willing to take.


  1. Who sponsored this review? It tries to sound like an impartial review, but sounds an awful lot like an advertisement combined with apology for producing an inferior tire in Gen2. Should we trust Gen 3? I currently run Continental ProContacts on my '07 335xi and would consider 3rd Gen Bridgestones but there is SO MUCH negative feedback on the earlier Bridgestones that I'm reluctant to spend over $1,000 on another mistake.


  2. I'm on the same page as you are. The review was done by autoblog. Hated the RFT just as well but like all bimmer owners, this seems too good to be true. The dealers don't seem to know much at all about this when i went to get my RFT patched. So we'll see when the 3rd generation hits town. Happy Bmotoring!