This is how Bridgestone describe the RE050A
"The Potenza RE050 RFT is Bridgestone’s Max Performance Summer run-flat tire developed exclusively for specific Audi, BMW, Maserati and Mercedes-Benz vehicles. The tire is designed to provide temporary extended mobility for a distance of 50 miles at up to 50 mph even after a puncture has allowed complete air pressure loss. Bridgestone developed the Potenza RE050 RFT to provide good traction along with responsive and predictable dry and wet road handling. It is not intended to be driven in near-freezing temperatures, through snow or on ice.
The Potenza RE050 RFT features a high-grip tread compound molded into a directional tread design. A continuous center rib, large tread blocks and stable shoulder elements provide responsive handling, high-speed stability and traction on dry roads, while circumferential and lateral tread grooves are aimed to pump water out from under the tire's footprint to minimize hydroplaning and aid wet traction.
The tire’s internal structure includes twin steel belts reinforced by spiral-wrapped nylon to stabilize the tread area and enhance handling, high-speed capability and ride quality. The structure of the Potenza RE050 RFT also features Bridgestone Side Support Run-Flat technology reinforced sidewalls to support the vehicle after a puncture causes a loss of air pressure.
or the ultimate drive it has to be Potenza S001, the ultimate
performance tyre. With new optimum block rigidity offering
better traction and improved braking performance, it combines
high-speed capabilities with a quiet, comfortable, safer ride."