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 A8
A sports-optimised ZF "6HP26-A61" six-speed tiptronic automatic transmission with "Dynamic Shift Programme" (DSP) and "sport" mode, with steering wheel mounted paddle-shifters, is the only offering. Output is transmitted via Audi's quattro generation IV all-wheel drive system, initially using the Torsen T-2 50:50 dynamic centre differential, and from 2007 for the 2008 model year, utilising the Torsen T-3 asymmetric dynamic centre differential, with a "default" torque distribution of 40 percent to the front axle and 60 percent to the rear. If the road conditions change, the purely mechanical differential responds without any delay; it can divert up to 85 percent of power to the rear wheels, and as much as 65 percent to the front wheels.