Luxury car makers are always trying to top each other with each new generation of vehicles, and recently the battle for supremacy has moved to the arena of transmissions. In 2001, BMW added a six-speed automatic to its 7 Series sedan, and then Mercedes upped the ante with a seven-speed two years later. Currently Lexus holds the crown with its eight-speed unit in the LS sedan, but now BMW and Audi are fighting back, and according to reports will offer eight-speed transmissions as early as 2009.

Both automakers are apparently looking to ZF to develop the transmission technology, and the German company says that due to longer gear ratios its unit will offer 14 percent better fuel-economy than a regular five-speed auto. With the U.S. CAFE standards looming and stricter emission regulations coming for Europe as well, the ZF transmission is seen as a way for luxury brands to make their powerful sedans more efficient.

Due to cost the eight-speed will only be offered in top-line models at first, but should make its way across each automaker's lineup as it becomes more affordable. BMW is supposedly readying the unit for its new 7 Series in 2010, and will add it to the surprisingly popular X6 SAC as well. Speculation is that Audi could make the transmission available in the A8 and Q7 SUV by 2009, as well as Ingolstadt's answer to the Mercedes CLS, the new A7 four-door coupe.

For its part Mercedes is sticking with seven speeds for the moment, though the company's head of passenger car engines and powertrains has said that adding an eighth is certainly possible. Some may feel that eight-speeds aren't really necessary for everyday driving, but as fuel-economy standards tighten, anything that can improve the efficiency of large, powerful luxury sedans is welcome. The only question is if an automaker raises the stakes with a nine-speed unit, how long will it take for the competition to follow suit?