Perpetual redesign is an ongoing theme at Porsche. The 997-generation Porsche 911 went through 24 variants in 7 years, and now the 991-generation (introduced last year) is on the 4th through 8th already. The biggest change is the introduction of all-wheel drive to the Carrera 4 and 4S models. The new ones are lighter than the previous generation, and also include the latest version of Porsche Traction Management (which, essentially, shows the driver how much traction each wheel is getting). Look for the new 911s to hit roads in February of 2013. [Car & Driver]
