Thread: DCT tranny
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      12-02-2012, 07:25 PM   #32
Major General

Drives: 340i M-sport AT
Join Date: Mar 2006
Location: Chicago

iTrader: (1)

Originally Posted by gthal View Post
Not debating the ability or benefit of the 8AT being able to downshift directly into a lower gear in auto mode but can it do it in manual mode? That is, if you are in 6th and want to go to 3rd, can you click the shift paddle 3 times and go to third? In the DCT you can. Even if the DCT has to engage intermediate gears it isn't noticeable. When I had my M3, the DCT would up/down shift immediately and could downshift multiple gears in manual mode instantly. The MCT in my C63 is fast but in manual mode can't "skip" gears and it is annoying when driving on a track or aggressively (and I would bet it is every bit as fast or faster than the 8AT in the BMW). The C63 auto claims to shift as fast as 100ms and it is very fast and responsive but it is no where near as responsive as the DCT in the M3 even if the shift speeds are similar... the 8AT is the same... a VERY fast auto but is not as immediate and responsive and direct as a DCT when in manual mode. DCT's cannot be matched in manual mode IMO as they are truly manual transmissions that shift at incredible speed.

My point is that for track/aggressive driving, the DCT is a better and more direct transmission and that is the only time multiple downshifts are needed (most modern transmissions have incredibly quick ""kick down" modes including the DCT). In that case, the only transmission that can do it in manual mode is the DCT... and it does it instantly. I do believe the 8AT is the better transmission for daily driving and is very fast and responsive. The DCT is the transmission of choice for track/aggressive driving IMO. I said this in another thread... there is a reason BMW has a DCT in the M3.
Yes, in manual mode the ZF AT can down shift from 6th to 3rd nearly instantly, just as fast as a dual clutch.
And, it can do it by skipping gears too.
A dual clutch can skip gears as well, but since the gears are on 2 shafts, then how fast it can go from an even number gear to a lower even number gear may require a couple of shifts, and/or take less than a split second quicker.
Can the ZF down shift faster than a dual clutch?
Maybe in some cases, but how much difference does it make is a good question.

I like dual clutch trans, and after having my ZF 335i for a while I'll bet I may like it better as there are still some times when I can feel the torque converter doing it's thing in this trans.
Shift speed is amazing for a torque converter AT, and rivals DCT's.

But, there is a difference in feel. A dual clutch feels more like an MT because it is basically an MT that is automated, but the engine is connected to the trans by a solid clutch/clutches.
The ZF AT, as you know, uses a torque converter so you still feel that especially when driving hard.
In day to day driving though, the ZF AT feels smoother because of the torque converter and how it can dampen the power transfer from engine to trans.
If BMW had offered a DCT and ZF sport AT, I would likely have gone with the DCT for the reasons I mentioned.

BTW, have you driven an F30 with the sport AT?
If not give it a try. It's VERY impressive for a torque converter trans.