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M2 Technical Topics > N55 Engine / Drivetrain / Exhaust / Bolt-ons / Tuning > DCT & SPORT+& HIGH REVS = rough shifts

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      06-23-2017, 10:58 AM   #23
MZWIE
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I agree with STEELIUS. In SPORT+ actually has more stick shock and torque loss. Which oddly enough totally invalidates the premise of quick shifts.

I've taken to always leave it in SPORT now. However, not sure how much difference SPORT+ makes to the chasis set up.
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      06-27-2017, 06:29 AM   #24
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Because of the shift shock and torque loss in S+ the shifts in S are faster. The shifts in S+ are so stunted.
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      06-27-2017, 07:34 PM   #25
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Quote:
Originally Posted by MZWIE View Post
Because of the shift shock and torque loss in S+ the shifts in S are faster. The shifts in S+ are so stunted.
Yes they often feel slower and the "donkey punch" just feels like it must be harming the transmission in some way. Maybe it's not but it feels quite violent, but more responsive than when I shift in sport.
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      06-29-2017, 11:16 AM   #26
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And another thing. Why does it make that awful "fart" sound when it shifts.
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      06-30-2017, 09:54 AM   #27
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Quote:
Originally Posted by MZWIE View Post
And another thing. Why does it make that awful "fart" sound when it shifts.
Because BMW programed it to do it. Its a glorious sound!
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      06-30-2017, 11:09 AM   #28
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Quote:
Originally Posted by MZWIE View Post
The difference between SPORT and SPORT+ for DCT shifts is big. In SPORT shifts are nice and crisp.

Currently not only are the shifts teeth rattling but also very embarrassing when having passengers. Every thinks there is something wrong with the transmission.

In SPORT+ it feels like a first generations SMG. I'm sure there must be a way to maintain fast shifts without the bang-bang.

I'm thinking some electronic value could be adjusted. Any ideas
To me...

Sport seems great for driving around or to work.

Sport+ for me only works well if rabbiting around and on ramps , other than that I don't use it on public roads. Though I do like how it holds gears and revs.

In traffic when the car is driving slow it still holds the gear when it should shift. Having a hard time explaining it but I could see that as being described as Sport+ & High Revs = rough shifts
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      06-30-2017, 12:51 PM   #29
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Quote:
Originally Posted by David1 View Post
Because BMW programed it to do it. Its a glorious sound!
I guess I always was thinking that DCT would be all about the fastest possible shifts without any gimmicks.

I want my DCT to behave like F1 cars. It is just a gear change that's it. Just do the job it was designed for. Having been to many F1 races, you will never hear "donkey kicks" or "farts".

All you hear is the change in pitch of the revs. It is, too me, one of the greatest sounds in the automotive world.
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      06-30-2017, 01:47 PM   #30
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Quote:
Originally Posted by omasou View Post
To me...

Sport seems great for driving around or to work.

Sport+ for me only works well if rabbiting around and on ramps , other than that I don't use it on public roads. Though I do like how it holds gears and revs.

In traffic when the car is driving slow it still holds the gear when it should shift. Having a hard time explaining it but I could see that as being described as Sport+ & High Revs = rough shifts

I just drive it in manual/sequential mode so it doesn't hold gears around town when I don't want it to. Still shifts "violently" at high RPM.
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      03-26-2018, 12:04 PM   #31
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Well, after my experience with my new M2 - 2400kms done, I do often use MDM mode (one click of DSC button) as I did with my previous car - M135i. Sport+ tries probably to shift faster, but scares me in full throttle sometimes destabilizing the car, while it is probably shitfing faster then engine rpms gets to lower rpms corresponding with next gear. Thats why we probably get that donkey kick. Anyone other opinion? Even in Motortrend test they made fastest lap time with MDM mode, 2s faster then with Sport+, if I do rember correctly and mentioning harsh drive in Sport+. So I am a little bit sad that BMW didn't made modes like in other M cars.

Last edited by rtr76; 03-26-2018 at 12:27 PM..
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      03-26-2018, 02:00 PM   #32
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It clearly shifts harder in Sport+ but I don't see the problem?
Maybe because I always shift manual?
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      03-26-2018, 03:18 PM   #33
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Quote:
Originally Posted by MZWIE View Post
I guess I always was thinking that DCT would be all about the fastest possible shifts without any gimmicks.

I want my DCT to behave like F1 cars. It is just a gear change that's it. Just do the job it was designed for. Having been to many F1 races, you will never hear "donkey kicks" or "farts".

All you hear is the change in pitch of the revs. It is, too me, one of the greatest sounds in the automotive world.
Well, that's just the sound it makes on the overrun. You don't have to shift to do it, just step off the gas for a bit, and you'll hear that. It happens for the split second the throttle is cut to shift gears.

Honestly, best thing about the car. But, good news for you is that you can remove it you flash, so look forward to that.
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      06-27-2018, 06:31 PM   #34
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There is no such thing as artificial rough shifting.

My theory (unverified) is that shifting time in S+ is reduced so the clutch connects a little earlier than rev matching is mechanically finished. Hence the kick-back feeling on upshift.

There is much less toughness on downshift because rev-up is much quicker (than rev-down) and is quick enough to catch up shifting time in S+.
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      06-27-2018, 07:27 PM   #35
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When I am in sport+ and on it the shifts seem seamless
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      06-27-2018, 08:20 PM   #36
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Quote:
Originally Posted by m2ruder View Post
When I am in sport+ and on it the shifts seem seamless
Poor you
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      06-28-2018, 07:42 PM   #37
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Here's a good paper to read explaining DCT shift behaviour. The "fart" is engine torque cut during shift, and the "donkey kick" is potentially caused by issues with synchronizing the clutch release/engagement.

https://www.springer.com/cda/content/document/cda_downloaddocument/9783319052625-c1.pdf
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      06-28-2018, 08:24 PM   #38
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You wouldn't happen to be lifting your foot off the throttle or disengaging the downshift button (overboost activator) in between shifts would you?

Mine shifts hard and crisp and will, yes, feel unstable in a sweeping corner upshifting from 2 to 3 or 3 to 4 under full throttle...that's the DSC saving your ass from a full counter steer power slide, it breaks traction for a split second and then engages traction and DSC for a split second. Try same with DSC off and shifts slow down in speed to "sport" mode to prevent you from doing a snap pirouette but will allow a beautiful full lock drift.

3rd set of tires put on at 18,000 miles

Last edited by M-Supra; 06-28-2018 at 09:29 PM..
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      06-28-2018, 08:26 PM   #39
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Quote:
Originally Posted by kivyee View Post
Here's a good paper to read explaining DCT shift behaviour. The "fart" is engine torque cut during shift, and the "donkey kick" is potentially caused by issues with synchronizing the clutch release/engagement.

https://www.springer.com/cda/content...9052625-c1.pdf
This explanation is line with my theory - S+ donkey kicks because clutch is done a little faster than rev match on upshift.

Fart is DV releasing boost to hot side. The quicker the shift is, the more aggressively the compressed air travels thru DV, hence the louder fart. Torque is not lost during the process. On the contrary, torque more often than not surge a little bit due to overload because boost sometimes isn't released by DV quickly enough in upshifting for lower rpm. Especially on flash tune, throttle plate is programmed to have a much higher interference threshold. DV is the only thing that's directly responsible for cold side adjustment.

Once people know how to read log, they will see it more clearly.
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      06-29-2018, 12:41 AM   #40
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Quote:
Originally Posted by MR_M2 View Post
I think Bmw has artificial kickbacks in sport+ mode. It doesn't have to be that way. You can be quick and smooth - PDK does it very well.
Bingo. Its just to make it feel sportier...pretty annoying and the main reason i got the manual gearbox
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      06-29-2018, 01:56 PM   #41
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Quote:
Originally Posted by Lukeni View Post
Bingo. Its just to make it feel sportier...pretty annoying and the main reason i got the manual gearbox
Seems like there would be a way through tuning or flashing to get sport shifts in Sport+
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      06-29-2018, 05:28 PM   #42
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Quote:
Originally Posted by Lukeni View Post
Bingo. Its just to make it feel sportier...pretty annoying and the main reason i got the manual gearbox
Sport+ is most aggressive mapping and full output of engine
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      06-30-2018, 01:29 AM   #43
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Quote:
Originally Posted by M-Supra View Post
Quote:
Originally Posted by Lukeni View Post
Bingo. Its just to make it feel sportier...pretty annoying and the main reason i got the manual gearbox
Sport+ is most aggressive mapping and full output of engine
there is no difference between sport and sport+ engine wise...and besides the sporty feeling there is no reason the dct has to shift so hard. It even spins the tires from 2nd to 3rd. Ridiculous
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      06-30-2018, 08:38 AM   #44
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I quite like the shift in sport+ but to compare the dct gearbox to f1 gearbox-which is seamless shift and the price of the gearbox cost more than the sum of our M2 is not a like for like comparison.
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