Bridgestone's Third Generation Run Flat Tire

By Thom Cannell
Senior Editor
Detroit Bureau
The Auto Channel

Run flats are back. Originally designed for the ultra exotic all wheel drive Porsche 959, the second generation of run flat tires were original equipment tires on daily drivers like Mini Cooper, Corvette, Lexus, BMW, and even a Sienna minivan. Unfortunately, though they delivered on safety and security—their promise that you could drive 50 miles at 50 miles per hour—very few owners liked them well enough to replace them with similar tires. Drivers complained that those tires felt heavy and wore quickly. They also disliked the way their cars handled although their vehicle suspensions were designed around run flats.

Recently Bridgestone introduce a third generation run flat tire, the Potenza RE960AS Pole Position RFT, with important changes that may encourage drivers to return to run flat tires, or even adopt them for their cars. Foremost, the tires weigh less and less unsprung mass always makes a car feel more nimble. Other notable engineering attributes include less stiffness in the tires sidewall and improved tire chemistry, along with some novel design features.

The RE960AS RFT uses new polymer technology that Bridgestone calls NanoPro-Tech. Conversations with Bridgestone, and competitors Michelin, Pirelli, and Goodyear reveals that all tire makers have upped the tire compounding game in the last decade, particularly in tread rubber. Compared to an Alton Brown cooking science demonstration, it’s like the creaming method of baking; adding precise amounts of ingredients (natural and man-made rubber, silica, carbon black, etc.) at the right time and agitating it a specific duration make the compound better. Bridgestone engineers say NanoPro-Tech results in rubber that, under a microscope, looks less like a ball made of rubber bands and more like a solid golf ball.

Sidewalls are the key to run flat tires; they must support a deflated tire for 50 miles of operation. With less mass and less sidewall stiffness, third generation run flats just feel better to drivers. Rejecting heat generation is another key development and these RE960 AS RFT tires minute cooling fins molded into the sidewalls. They disturb airflow at the sidewall for improved cooling, inflated or not. Engineers say the tire operates 20°F cooler (151°F vs. 172°F) and that it has much improved wear and is actually comparable to their premium all weather RE960AS non run flat tire. So, for the first time in history, Bridgestone offers a 40,000 mile tread warranty.

There are other improvements. This tire tread includes more silica, which improves overall grip, particularly in wet weather. The compound is molded to create two layers, a high grip outer layer and, as the tire wears, it exposes a second layer with even greater wet grip. We’ve tried new and worn dual-layer Bridgestones and this claim holds true.

We briefly tested the new tire in Phoenix and were very impressed. The new RE960AS RFT run flat seemed quieter than its non-run flat counterpart when inflated, and it seemed to produce, in the cabin of a BMW 3 Series, less high frequency hash. It even felt a bit softer riding. When deflated, and we checked the tire gauge, there was no discernible difference in steering or handling on smooth pavement, rough pavement, driving through sweeping or abrupt turns. Having a functional Tire Pressure Monitoring System is critical. And, by the way, should your run flat tire go flat you need to have it dismounted and checked as soon as possible. Driving on a deflated tire, run flat or not, quickly ruins it. Run flats, if driven minimally, may be reparable by a well equipped shop, but only after a full dismount and inspection.

The new tire will launch this summer in nine sizes to fit, primarily, their original fitments of MiniCooper, Corvette, some Lexus and BMW models, and AWD Toyota Sienna minivans.