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      09-20-2014, 03:25 AM   #1
MWS55
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Bucking while accelerating - DCT?

When I have M Engine Dynamics set to Sport Plus and Drivelogic set to S3, the car bucks under heavy acceleration. Anyone else?

Last edited by mkoesel; 09-20-2014 at 07:29 AM.. Reason: Readability/Clarity
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      09-20-2014, 04:46 AM   #2
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Yes it's very sensitive/ jumpy. I've learned to feather it out if I'm not hammering on it from a dead stop.
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      09-20-2014, 05:22 AM   #3
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It can be jerky but it's mostly user error.
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      09-20-2014, 05:51 AM   #4
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My E90 did the same thing. Sometimes so badly, it made me look like a novice stick driver with a touchy clutch.
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      09-20-2014, 07:06 AM   #5
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It's user error, once you push it down hard the traction kicks in and makes you take your foot off the gas and press is back again which makes the car jerk.
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      09-20-2014, 07:21 AM   #6
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1st gear is extremely short on the F8X DCT (to the point of being pretty useless IMO). It helps keeping things smooth in low speed low power conditions. However, if you mash it, it can get jerky.
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      09-20-2014, 07:36 AM   #7
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One thing you could do is try using Comfort mode while accelerating from a stop. It's very easy to change using the button on the console. Switching the Drivelogic mode may help too. Finally, you can just launch from second gear instead if you wish.
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      09-20-2014, 10:21 AM   #8
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Middle position on the shift selector will dial it down a bit or put it in the fist (lowest or 1 bar) position for the shift and you will be fine. All sport mode in parking lots is a skittish place. Just leave engine on sport and all other comfort you have the enhanced sound but smooth ride in low speed areas.
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      09-20-2014, 10:25 AM   #9
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Yeah this happens sometimes and it's rather embarrassing. I've gotten good about immediately upshifting or backing off the throttle when I detect that it's happening
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      09-20-2014, 10:26 AM   #10
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Quote:
Originally Posted by CanAutM3
1st gear is extremely short on the F8X DCT (to the point of being pretty useless IMO). It helps keeping things smooth in low speed low power conditions. However, if you mash it, it can get jerky.
My friend did gearing calculations on the M4 vs the M6 and his C7 vette . The M4 is 12% shorter than the M6 in every gear . First in the M4 is 65% shorter than in the vette despite the C7 making 50lb feet more tq . And the DCT M4 2nd is barely taller than the vettes first gear lol . It's crazy short gearing .
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      09-20-2014, 11:04 AM   #11
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I am pleased I am not the only one. I thought I had lost my touch
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      09-20-2014, 02:35 PM   #12
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Originally Posted by Wregie View Post
I am pleased I am not the only one. I thought I had lost my touch
haha same here, doesn't do it all the time but good to know
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      09-20-2014, 02:38 PM   #13
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Originally Posted by trinim3 View Post
Yeah this happens sometimes and it's rather embarrassing. I've gotten good about immediately upshifting or backing off the throttle when I detect that it's happening
It is man specially taking off while everyone checking out your car Makes you look like you can't drive the car...
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      09-20-2014, 02:46 PM   #14
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Quote:
Originally Posted by CanAutM3 View Post
1st gear is extremely short on the F8X DCT (to the point of being pretty useless IMO). It helps keeping things smooth in low speed low power conditions. However, if you mash it, it can get jerky.
Word..
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      09-20-2014, 02:50 PM   #15
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I found the same... Thought there was something wrong with the tranny lol
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      09-20-2014, 03:13 PM   #16
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Very common. All user error - myself included.

I've just become accustomed to using Sport when going from light to light and sport + when on open road.
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      09-20-2014, 06:51 PM   #17
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Do not use S3/D3 mode. That is just too harsh and has no practical use. It is only there for the sake of proving fast shifts on paper. Even track drivers stay in S2.

There's no point in gaining 5 milliseconds faster shifting time if you're completely upsetting the entire chassis with the jolt, losing composure, traction, etc.
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      09-23-2014, 01:13 PM   #18
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As the bucking happens in 1st gear it has nothing to do with the shift settings though I agree in some situations setting 3 can upset the chassis. The problem is that the throttle response in Sport+ is a bit keen. If you hit the slightest bump when accelerating in first it causes a slight throttle adjustment. if the car decelerates inertia sends your foot forward you unconsciously back off and inertia sets up the on off situation which Kangaroos you down the road. I have found it is better if you drive with much more of a bent leg (i.e. closer to the throttle) but this is not ideal for me as I am too close to the wheel (Short arse).
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      09-23-2014, 10:45 PM   #19
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Throttle induced oscillation. It was first noticed with the E39 M5.

Your foot moves ever so slightly back and forth that is hardly noticeable, but it gets into a rhythm with the throttle and causes the bucking.
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      09-24-2014, 07:44 AM   #20
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I experienced this first hand last night in my test drive and a light bulb went off in my head "I just read about this!".

The CA with me said as it happened: "Oh, no worries, the last person who drove this left the throttle in Sport +". We put it back down to sport and all was back to normal.

I felt like such a noob driver, lol (which admittedly and comparatively to many I probably am).
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      09-24-2014, 11:04 AM   #21
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My kids got a good laugh at my expense when this happened to me. Yeah, it was like I was a brand new stick driver. Pretty embarrassing.
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      09-24-2014, 11:14 AM   #22
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Quote:
Originally Posted by rz3 View Post
My kids got a good laugh at my expense when this happened to me. Yeah, it was like I was a brand new stick driver. Pretty embarrassing.
LoL, our kids will never meet, let's make sure of that!!

"Mum, can you drive at all? I know this car wants to go, and doesn't do slow, but that's just so baaaaaaad"

I've even stalled it once, though then I had forgotten it was on already. Thank god I was surrounded by M geeks and not my kids, the ripping from the last would've been worse.
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