Unlike other manual transmissions, the Audi TT DSG transmission has two multi-plate clutches. One connects to the 1st, 3rd and 5th gear shaft and the second connects to the 2nd, 4th and 6th gear shaft. This allows smoother and faster shifts than a conventional manual gear box. By simultaneously disengaging one clutch and engaging the other, the transmission shifts seamlessly from one gear to the next without pausing. Upshifts take only eight milliseconds (10 times faster than BMW's SMG transmission), making it the fastest shifting manual that is currently available. The automated manual gear boxes are still fairly new, so it may be awhile before you see them. But sooner or later, late-model vehicles equipped with these state-of-the-art electronic manual gear boxes will be out of warranty and in your shops for repairs. In the meantime, there are plenty of conventional 5-speed and 6-speed manual transmissions to keep you busy.
Continuously Variable Transmissions (CVTs) have been around since the 1980s and have long been used in snowmobiles. In recent years they have been appearing in more and more cars. Subaru offered a CVT transmission in the Justy, as did Ford in the European version of the Fiesta. Newer vehicles that have CVTs include certain Honda Civic models, Nissan Maxima and Altima, MINI cooper and others. CVTs have several important advantages compared to automatic transmissions. They are smaller, lighter and cheaper to build. Compared to a manual transmission, a CVT offers an infinite range of gear ratios and no shifting is required. But a CVT does not work like a manual or an automatic. Consequently, it creates a rubber band effect where the engine revs up when you step on the gas as the transmission gear ratio changes. It creates the sensation of a clutch that is slipping or an automatic with an overly sensitive passing gear.
Durability limits how much horsepower a CVT can safely handle. A steel belt that rotates between a pair of pulleys must be strong enough to handle the engine's power output. For small displacement engines (3,500 cc or less), current CVTs are up to the task. But for larger displacement high-output high torque engines, a manual or conventional automatic transmission is still required. Audi's Multitronic CVT, which is offered in the A6 model, uses a chain instead of a belt to carry the power between the pulleys, and a special torque sensor to control the force with which the pulleys grip the chain. The steel chain has 1,025 link plates, 75 pairs of pins and can handle up to 221 ft.-lbs. of torque. Audi also programs its CVT computer to reduce the rubber band effect so the driver feels less of a disconnect between engine rpm and vehicle speed. The Multitronic also has a manual shift mode that allows the CVT to be shifted like a manual 6-speed gear box, including downshifts to use engine braking to slow the vehicle. Another twist on CVT technology is Nissan's Extroid transmission. Instead of using a belt or a chain, the Extroid transmission uses a pair of rotating rollers between an input disc and an output disc. A special oil is used to provide both lubrication and friction between the rollers and discs. Varying the angle of the rollers changes the gear ratio of the transmission. Introduced on the Nissan Cedric/Gloria and Skyline 350GT-8 in Japan, this design reportedly can handle higher torque loads (up to 286 ft.-lbs.) and comes with a manual mode that simulates a manual 6-speed transmission.