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 RS 4
Noticeable changes to the B9 included a more angular exterior, newly designed wheels, and a new turbocharged 2.9 V6 engine. Unlike the pre-facelift B8 RS4 which had a 7-speed dual-clutch S-tronic transmission, the B9 RS4 is available with an 8-speed torque converter tiptronic automatic.