Both the front and rear end of the A4 are all ... and a new trick center differential on the S4. The A4 Avant (station wagon, in Audi-speak) is discontinued for 2013, though it does live on ...

The 2015 Audi S4 is an all-wheel-drive sports sedan that is the performance variant of the A4. Its sole powertrain ... and the optional sport rear differential. In a 2013 First Test we said ...