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12-14-2009, 06:50 PM | #23 | |
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2020 M2 Comp, Sunset Orange/Blk: Orange stitching, DCT, exec pkg, bicolor rims Gone '18 M550i, '16 X4 M40i, '15 M5, '13 X3 35i, '12 335is, '11 X5 50i, '09 Z4 35i, '08 550i, 06 X3, 06 650i, '02 M5, '99 540i |
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12-16-2009, 11:15 AM | #24 |
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As far as I can guess (technical guys correct me if i'm wrong), in the DCT, if you take your foot off the accelerator pedal, the car prepares itself for the downshift as the second clutch prepares for the lower gear. If you change your mind at that moment and hit the pedal, this creates the lag until the second gear engages with the higher gear, and then the car delivers the power (like a second late). Still it doesn't explain why the car waits to deliver any power in the current gear...
I guess although D mode is nice, I might end up much more at the M mode than I would have liked. |
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12-16-2009, 08:36 PM | #25 | |
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With the DCT, it should always be engaged in the current gear. Yes, its possible the second clutch does shift between one gear lower and one gear higher based on the throttle but the DCT should not be causing a lag when hitting the gas. What RPM do you experience the lag at? At 1500-2000 RPMs, there could be a brief moment before the turbo(s) spool up. Above 2500 or 3000, throttle response seems instantaneous. I will play with it tomorrow and report back.
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2020 X3M non-comp, Alpine White over black : Exec Pkg, ventilated M Sport seats, 20"s
2020 M2 Comp, Sunset Orange/Blk: Orange stitching, DCT, exec pkg, bicolor rims Gone '18 M550i, '16 X4 M40i, '15 M5, '13 X3 35i, '12 335is, '11 X5 50i, '09 Z4 35i, '08 550i, 06 X3, 06 650i, '02 M5, '99 540i |
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12-17-2009, 02:28 AM | #26 |
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When downshifting (or upshifting) two gears at the time you may experience shiftlag because the system can prepair only one gear at the time. This is a little downside of the dual clutch automatic gearbox.
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12-17-2009, 08:04 AM | #27 |
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In performance driving, there were very few occasions that I dropped the gears more than one at a time. It was always 6-5-4. . . and not 6-3. . . unless I slowed very fast, brakes only and no assist from the engine to decelerate. Even then, you had to match your revs to avoid blowing your engine, gearbox or rear end. All of this took time and concentration, right?
So, think about it - you opted for a smooth and sophisticated piece of technology that takes a millisecond or two that previously would have taken manually, all total including clutching-shifting-rev match-declutching (repeat), 3, 4 or 5 seconds, or more. You wouldn't even think about it. Now, your waiting on the machine to do magic for you and get impatient. A pure automatic wouldn't be any faster and a lot less satisfying. You guys may be blaming the DCT for a slight turbo lag as the engine revs back up following an up or down shift. or, maybe there's something wrong with your cars. . . . Last edited by teagueAMX; 12-17-2009 at 07:15 PM.. |
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12-17-2009, 08:12 AM | #28 |
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If you are upshifting 2 gears at once, then you must be leasurely driving along, in which case why would you care if there were a minute amount of shiftlag? Just a thought.
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12-17-2009, 09:20 AM | #29 |
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I love the DCT - amazing transmission and technology. I agree with the post above - you notice a slight "lag" because in a MT you would be participating physically in the lag instead of waiting for a split second with the DCT, doing nothing but having your foot on the accelerator.
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12-17-2009, 11:38 AM | #30 |
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upshifting by 2 gears, yes, lazy shift, downshift by 2 gears, it happens in sharp turns ...
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12-17-2009, 12:48 PM | #31 |
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12-17-2009, 07:36 PM | #32 |
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Yes, that's true, if you get into a real sharp turn and drop a lot of speed. But that also means you're likely coasting through part of the turn and engine rpm's have dropped to idle or close to it. No doubt the DCT may be a little confused and slight turbo lag plays a role. . .
If you downshift into mid-power band gear ratio (2500-3500 rpm) the turbos will blow a mighty wind and lag is minimized. |
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12-23-2009, 10:28 PM | #33 |
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i have noticed that in sport + mode if you are driving aggresively and hit the brake little hard for a turn the DCT downshifted for you much faster it will keep the RPM at around 3,000.
i noticed that the other day. can anyone maybe confirm? |
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12-24-2009, 08:41 AM | #34 | |
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I would think that your description is a good thing for sport driving. Although when I am doing any "spirited" driving I am usually in M mode and do any downshifts myself prior to corner entry.
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2020 X3M non-comp, Alpine White over black : Exec Pkg, ventilated M Sport seats, 20"s
2020 M2 Comp, Sunset Orange/Blk: Orange stitching, DCT, exec pkg, bicolor rims Gone '18 M550i, '16 X4 M40i, '15 M5, '13 X3 35i, '12 335is, '11 X5 50i, '09 Z4 35i, '08 550i, 06 X3, 06 650i, '02 M5, '99 540i |
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