Audi S4
Audi's quattro four-wheel-drive system was standard on the C4 S4/S6; a first-generation Torsen-based system which used the "T-1" automatically biasing centre differential (ATB) was used on vehicles equipped with manual transmissions, while a transfer box based system was used on vehicles equipped with an automatic transmission.
Audi S6
In late 1997, Audi introduced an all-new range of Audi A6 models, based on the Volkswagen Group C5 platform. A new Audi S6, now officially known as the Audi S6 quattro appeared in 1999, to complement its A6 platform-mate. It was available in a four-door saloon/sedan and a five-door Avant (estate/wagon). In North America, the Avant bodystyle was the only version available. The vehicle could accelerate from standstill to in 5.7 seconds, and from 0 to in 21.7 seconds. The top speed was electronically governed to .