March 25, 2011
BMW and a few other vehicle manufacturers have been equipping their vehicles with run-flat tires as they leave the factory. While run-flat tires are designed to give drivers peace of mind in the event of unexpected air loss, they do come with a few tradeoffs, primarily in the form of reduced ride quality.
Bridgestone is a long-time supplier of run-flat tires as Original Equipment on a variety of vehicles, affording
plenty of opportunity to tune and develop the performance characteristics of their run-flat tire designs.
Traditional self-supporting run-flat tires feature a very thick sidewall design, necessary to support the weight
of the vehicle in the event of air loss. Even when properly inflated, this thicker sidewall reduces the tire’s
ride quality versus a conventional non-run-flat tire. Bridgestone’s new third generation (3G) run-flat design
used in the Potenza RE960AS Pole Position RFT features a thinner sidewall that minimizes the run-flat tire’s
negative impact on ride quality. While still thicker than a conventional tire, the signature features of the 3G
run-flat sidewall are a unique exterior cooling fin design and special rubber compound, both designed to reduce
the heat buildup that occurs while driving on the tire uninflated. Reduced heat buildup during run-flat
operation allows for the thinner sidewall design, ultimately improving ride comfort versus previous generation
run-flats.
We compared the ride quality of properly inflated Potenza RE960AS Pole Position RFT run-flat tires with the
conventional non-run-flat version of the same tire, using BMW 328i sedans (which come standard with run-flat
tires) fitted with 225/45R17 tires. Driving over a variety of man-made and natural surface ripples, undulations,
bumps and broken pavement revealed some interesting differences, and notable similarity between the two tires.
When driving over small irregularities the run-flat tire displayed very good ride qualities, but allowed a
little more of the bump’s texture to find its way to the driver than the non-run-flat tire. Medium-sized bumps
were harder to distinguish a difference between the two, and the impact of the largest bumps felt equivalent.
Interestingly, when driving across a section of undulating pavement the vertical movement of the car felt more controlled on the run-flat tire. Initial steering response also felt a little better with the Potenza RE960AS Pole Position RFT run-flat, as this tire responded more directly than the (also good) conventional tire.
Our time driving on the new Potenza RE960AS Pole Position during this preview was limited, and didn’t provide the opportunity to get to know all of its characteristics. We’re looking forward to a comprehensive Real World Road Ride and Performance Track Drive at Tire Rack in the coming test season.
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