What's a double-clutch gearbox?

And how does it work (particularly from the driver's standpoint)? I've seen this mentioned in articles about some high-performance cars and have wondered what it was all about.

West Philly Forever, Philadelphia

Double-clutch transmission” is BMW’s name for an automated-manual transmission, which is constructed like a manual transmission but can shift automatically and has no clutch pedal. The advantage to this type of construction is that you get an automatic that shifts extremely quickly compared to a traditional automatic, takes up less space and also weighs less. If you think that sounds like a transmission oriented toward performance, then you’re correct, as that’s the kind of car you’ll typically find equipped with this transmission.


There's also a single-clutch automated manual that's used in cars like the Smart ForTwo. In some applications a single-clutch may not be as smooth as a dual-clutch because the clutch has to disengage, choose a gear then re-engage. With a dual-clutch setup the next gear can be staged and ready to shift before you're even out of the previous gear, so there isn't an awkward hesitation like what's experience in the Smart.

You may also hear a double-clutch transmission called dual-clutch, clutchless manual, twin-clutch, etc. As previously mentioned, you get quick shifts, but for drivers it means there’s no clutch pedal and shifting can be controlled through either paddle shifters on the steering wheel or via a plus/minus gate on the shifter. You don’t, however, have to use the paddles or plus/minus gate; most cars with these transmissions also have an automatic mode, where the transmission will shift on its own like a regular automatic. Shifting on its own is where you’ll find the downside to these transmissions, as sometimes that shifting can be jerky or feel unnatural in day-to-day driving.

2008 and 2009 vehicles that are or can be equipped with an automated-manual transmission (both single-and dual-clutch) include:

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Answered by Joe Bruzek on May 9, 2008 in How Does That Work? , I'm Just Wondering | Permalink

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