Bucking while accelerating - DCT?

[captainaudio]

Originally Posted by Fly4Tarpon

. I sometimes fishtale a bit switching gears. Thats FUN! I would HATE this car if it had a slushbox like my Cayenne GTS has.... that 8 speed "tiptronic" is a mushy boring piece of garbage. The PDK porshe tranny is MUCH more fun like our DCT.

It may be fun when you are driving at 6/10 but when you are at the limits it will upset the car. The last thing I want is a car with a transmission that emulates a poorly driven MT.

[Needsdecaf]

Originally Posted by Rick955

Thanks, Captain. I know there is no P, and also read about the creeping forward/rolling back aspects. But if it's in D, I was assuming that it functions pretty much is like any AT, (with those exceptions you noted).

A few things that are different.

Some of the posters above are steering you off track. I mentioned the torque converter not because it's the only way to get smooth take offs, but because of HOW IT WORKS. A torque converter uses two "fans" essentially, spinning in fluid (ATF). Very simply put, the "fan" on the engine side spins as the engine speeds up. At first, nothing happens. But as the "fan" spins faster, the fluid's shear eventually starts to transmit force to the other "fan" and the wheels receive power. This is very gradual and soft, hence "smooth starts". At some point, the two sides will lock together using a clutch, and you will have no loss due to the heat in the fluid.

Because the DCT has no torque converter, it uses a clutch to engage the drive side (engine) to the driven side (wheels) (two actually, one for odd gears, the other for even). So it's engagement behaves the same way that a manual transmission would. Here is the difference.

In a traditional manual transmission, the driver is in charge of two things, throttle and clutch. You choose how many revs to add, and how quickly or gradually to engage the clutch. You control the smoothness of the engagement.

In the DCT, you still control the throttle, but the computer controls the clutch. It needs to guess your intentions based on throttle input. So, if it senses you rolling into the throttle, it'll engage the clutch slowly. Jam into the throttle, and it'll slam the clutches shut, expecting that you'll want a fast takeoff.

So the trick is that you need to work simpatico with the computer that's engaging the clutch. Since there is no fluid filled torque converter damping out any differences, you're going to feel when you and the computer are at odds with one another.

I won't get into shifting underway, as that's usually not as much of an issue.

Hope this helps.

[captainaudio]

Originally Posted by Needsdecaf

A few things that are different.

Some of the posters above are steering you off track. I mentioned the torque converter not because it's the only way to get smooth take offs, but because of HOW IT WORKS. A torque converter uses two "fans" essentially, spinning in fluid (ATF). Very simply put, the "fan" on the engine side spins as the engine speeds up. At first, nothing happens. But as the "fan" spins faster, the fluid's shear eventually starts to transmit force to the other "fan" and the wheels receive power. This is very gradual and soft, hence "smooth starts". At some point, the two sides will lock together using a clutch, and you will have no loss due to the heat in the fluid.

Because the DCT has no torque converter, it uses a clutch to engage the drive side (engine) to the driven side (wheels) (two actually, one for odd gears, the other for even). So it's engagement behaves the same way that a manual transmission would. Here is the difference.

In a traditional manual transmission, the driver is in charge of two things, throttle and clutch. You choose how many revs to add, and how quickly or gradually to engage the clutch. You control the smoothness of the engagement.

In the DCT, you still control the throttle, but the computer controls the clutch. It needs to guess your intentions based on throttle input. So, if it senses you rolling into the throttle, it'll engage the clutch slowly. Jam into the throttle, and it'll slam the clutches shut, expecting that you'll want a fast takeoff.

So the trick is that you need to work simpatico with the computer that's engaging the clutch. Since there is no fluid filled torque converter damping out any differences, you're going to feel when you and the computer are at odds with one another.

I won't get into shifting underway, as that's usually not as much of an issue.

Hope this helps.

This is a very good description but will stick to my point that if you put the car in drive and are conservative with the throttle the DCT will act very similar to a Steptronic.

[minn19]

Originally Posted by captainaudio

This is a very good description but will stick to my point that if you put the car in drive and are conservative with the throttle the DCT will act very similar to a Steptronic.

In normal D1 driving I don't really notice a difference from my 335s ZF8. I have not experienced any of the jerkiness that some are describing here.

[CanAutM3]

Originally Posted by minn19

In normal D1 driving I don't really notice a difference from my 335s ZF8.

Really

How about when you lift off the brake when the vehicle is stationary, does the DCT creep forward as the ZF8 did?

[M6-Coupe]

Originally Posted by CanAutM3

Really

How about when you lift off the brake when the vehicle is stationary, does the DCT creep forward as the ZF8 did?

Bingo... This is more than enough reason why I love DCT over ZF8

[minn19]

Originally Posted by CanAutM3

Really

How about when you lift off the brake when the vehicle is stationary, does the DCT creep forward as the ZF8 did?

No it doesn't. I was more comparing the two on smoothness while shifting and starting off. The only difference I notice is when the car isn't warmed up it feels like the clutch in the DCT is slipping. This goes away quickly when it warms up.

[Blksnowflake]

Originally Posted by Needsdecaf

A few things that are different.

Some of the posters above are steering you off track. I mentioned the torque converter not because it's the only way to get smooth take offs, but because of HOW IT WORKS. A torque converter uses two "fans" essentially, spinning in fluid (ATF). Very simply put, the "fan" on the engine side spins as the engine speeds up. At first, nothing happens. But as the "fan" spins faster, the fluid's shear eventually starts to transmit force to the other "fan" and the wheels receive power. This is very gradual and soft, hence "smooth starts". At some point, the two sides will lock together using a clutch, and you will have no loss due to the heat in the fluid.

Because the DCT has no torque converter, it uses a clutch to engage the drive side (engine) to the driven side (wheels) (two actually, one for odd gears, the other for even). So it's engagement behaves the same way that a manual transmission would. Here is the difference.

In a traditional manual transmission, the driver is in charge of two things, throttle and clutch. You choose how many revs to add, and how quickly or gradually to engage the clutch. You control the smoothness of the engagement.

In the DCT, you still control the throttle, but the computer controls the clutch. It needs to guess your intentions based on throttle input. So, if it senses you rolling into the throttle, it'll engage the clutch slowly. Jam into the throttle, and it'll slam the clutches shut, expecting that you'll want a fast takeoff.

So the trick is that you need to work simpatico with the computer that's engaging the clutch. Since there is no fluid filled torque converter damping out any differences, you're going to feel when you and the computer are at odds with one another.

I won't get into shifting underway, as that's usually not as much of an issue.

Hope this helps.

^This is the answer.
And here's my .02 cents worth of opinion as I have figured out a little more of why it bucks as stated above with some of my experience with this tranny, having broke the car in finally I realise this car likes to rev....if you step on it whether you're smoothly pressing into the throttle or stomping it only to slightly back off as you go into second gear(manual or auto) the DCT gets confused at your intentions.....do you want to "go"....or not....

If you rev the engine out I promise you the jerkiness/bucking will smooth out. If you want to do two second bursts from the light.....bad move, the DCT doesn't like this....it wants and thinks you wanted to "go"....but then you backed off...thus leaving it hanging....so it bucks and jerks in an attempt at quickly sort of trying to work out whether it should shift up or down or if in manual whether to slam the next gear in now or just be "prepared" for the next gear.

It has nothing to do with whether people came from previously driving a DCT car or not, this transmission and engine have a learning curve. I bet most are bucking and jerking with the throttle in Sport or Sport +.......or have the DCT in the second or third setting....yet when they roll the throttle on as smooth as you want to be....but back off just as the revs climb then the jerking begins....which is why a lot are saying to quickly shift to second....yeah that will work but it isn't the answer....

You either want to go...and keep "going" with your settings "other than comfort" or you don't, in which case you should have all your settings in the most comfort settings. This is almost a racecar...almost....except with a shit ton of creature comforts and maybe four doors.

Try it...keep your settings higher than comfort and leave that light with your foot on the gas and don't let off, but "conservatively" shift at 4-5k to second, smooth as butter....
or
Put everything in soccer mom mode and leave that light like your in a school zone at 8am.....smooth as butter...
but...switch settings to sport and leave from a stop like a drag strip but let off to go in a school zone while the revs climb and the DCT is like WTF....."tease!" = buck/jerk....

Remember, you have all the torque at 1850rpms....that's ludicrous....bottom line, learn to drive your car and drive with correct intention, no half assing.

[Tonymiabmw]

Dude if you want 0 feel from the transmission get a 335 with and automatic transmission. The jerkiness is the clutch engaging! I hope BMW never makes the DCT feel like an automatic. Anyone that has owned an M or understands what a sports car is supposed to feel like would never say this transmission Is jerky.

[Lups]

Originally Posted by Tonymiabmw

Dude if you want 0 feel from the transmission get a 335 with and automatic transmission. The jerkiness is the clutch engaging! I hope BMW never makes the DCT feel like an automatic. Anyone that has owned an M or understands what a sports car is supposed to feel like would never say this transmission Is jerky.

Dude not us who drive manuals. IF not to give credit to the poor gasoline sold here, we don't know what you're on about. it's smooth. like ice cream.

[captainaudio]

No transmission should ever feel jerky whether it is an AT a DCT or an MT. I don't know why some people equate rough shifts with performance. Fast driving is smooth driving, jerkiness and roughness scrub off speed and upset the balance of the car,

[CanAutM3]

What does not help is the uselessly short first gear ratio.

I have ranted many times about BMW going cheap by giving us a "hand-me-down" DCT from the F1X M5/6.

[Needsdecaf]

Originally Posted by captainaudio

This is a very good description but will stick to my point that if you put the car in drive and are conservative with the throttle the DCT will act very similar to a Steptronic.

Yes, it quickly (to me) becomes second nature as to how the computer is going to react, and it works much like a normal automatic. But better. But the poster I was responding to wanted to know what was different, and what differences to expect. Pretty much, if he follows the thought of what I wrote, he will never have issues with jerkiness. As others mentioned, there is no creep, and if you feed in the throttle slowly,,you'll get a sense of the clutch biting. You do not get this sense with a torque converter auto.

As I said, and as you alluded to, once underway, shifts in D1 are very similar to those of the ZF8. Downshifts are noticeably better, IMO.

[Rick955]

Originally Posted by Needsdecaf

Yes, it quickly (to me) becomes second nature as to how the computer is going to react, and it works much like a normal automatic. But better. But the poster I was responding to wanted to know what was different, and what differences to expect. Pretty much, if he follows the thought of what I wrote, he will never have issues with jerkiness. As others mentioned, there is no creep, and if you feed in the throttle slowly,,you'll get a sense of the clutch biting. You do not get this sense with a torque converter auto.

As I said, and as you alluded to, once underway, shifts in D1 are very similar to those of the ZF8. Downshifts are noticeably better, IMO.

Thanks, all. I've had plenty of manuals, and of all the autos, the ZF8 is indeed the best AT I've used. Gonna be very exciting to use the DCT and I'll do as you all suggest above and keep those things in mind, especially when trying out the higher modes.

[captainaudio]

Originally Posted by Needsdecaf

Yes, it quickly (to me) becomes second nature as to how the computer is going to react, and it works much like a normal automatic. But better. But the poster I was responding to wanted to know what was different, and what differences to expect. Pretty much, if he follows the thought of what I wrote, he will never have issues with jerkiness. As others mentioned, there is no creep, and if you feed in the throttle slowly,,you'll get a sense of the clutch biting. You do not get this sense with a torque converter auto.

As I said, and as you alluded to, once underway, shifts in D1 are very similar to those of the ZF8. Downshifts are noticeably better, IMO.

Two quotes from automotive journalist and legendary race driver Denise McLuggage apply here.

1. "Drive what you're in"
2. "If what you are doing isn't working try something else"

The M3/4 needs to be approached cautiously and carefully, When driven conservatively it can be very docile and to many drivers it will seem very much like a regular 3/4 series. But never forget than when provoked it can turn on you very quickly.

CA

[M3maniac20]

Like people have said, the DCT just definitely takes some getting used to. It doesn't drive like anything else. You'll find the sweet spot.

[pr0gi]

no problem at all. Maybe because I do what some have said about the "speaking" my intentions to the computer. I've found out that if you treat the car more like a manual you get better results or at least I am. I remember when doing my driving exam the examiner told me i shift like AT
Anyway, just know what you want from the car. For smooth start dont hit hard the throttle back off and expect everything to be super smooth, be gentle like it's a woman

[erind]

Originally Posted by pr0gi

no problem at all. Maybe because I do what some have said about the "speaking" my intentions to the computer. I've found out that if you treat the car more like a manual you get better results or at least I am. I remember when doing my driving exam the examiner told me i shift like AT
Anyway, just know what you want from the car. For smooth start dont hit hard the throttle back off and expect everything to be super smooth, be gentle like it's a woman

Some women don't want you to be gentle

On topic:
I like the DCT. I know it can be jerky sometimes. I had the same issue when I got the M4. Now is a different story. Its like they said. You have to communicate with the car and find the sweet spot. After you find it its really nice

[afadeev]

Originally Posted by M6-Coupe

Bingo... This is more than enough reason why I love DCT over ZF8

Actually, this is the least of my concerns - you still need to sit on the brakes at a stop light on not perfectly even intersections (which are ~50% of my commute). Also, ZERO jerkiness for me on takeoff, but I do take it very easy for the first few miles until the car warms up, and I get out of the school zones.

And I do find that F80 DCT in the most docile setting is as smooth as ZF8, and works perfectly in 'auto' D mode.

a

[M6-Coupe]

Originally Posted by afadeev

Actually, this is the least of my concerns - you still need to sit on the brakes at a stop light on not perfectly even intersections (which are ~50% of my commute).

You are right but I was talking about "feeling"... the difference between rolling (the same as MT) and creep (torque converter)...

[GrussGott]

Originally Posted by minn19

No it doesn't. I was more comparing the two on smoothness while shifting and starting off. The only difference I notice is when the car isn't warmed up it feels like the clutch in the DCT is slipping. This goes away quickly when it warms up.

^ This is actually the correct answer. Needsdecaf gave a great write up, and while it excellently explains the mechanics of it, there is variability in behavior that's not addressed...

Once we clear away the "dude you suck" answers, the "jerky start" is a good question if cold-start jerkiness is what the OP is getting at ...

On the E9x - cold-start-then-drive was jerky as hell no matter what mode (and no matter what is going on technically). My wife hated that car, and it was DEFINITELY slipping the clutch. Anyone who's driven a MT for years knows the sound when you take your foot off the clutch slowly ... or you drive a new stick you've not been in before and you can overrev-overslip on your first go. Well the E9x did that big time and then gave you a very touchy throttle for about 60-120 seconds on cold start. There was no driving style to fix it except just letting the car warm up.

The F8x is WAY better. It also does a bit of clutch slipping as minn19 notes but it's much less noticeable and much easier to control than in the E9x. Also I've noticed that the F8x goes for second gear right away. Anyway, my wife says the jerkiness is gone but I suspect that's only because she had to occasionally drive the E9x for 3 years

So in my experience it's the combo of Needsdecaf and minn19 that's the right answer.

[antych]

I'm new to DCT (drove 335i auto before) and I experienced some jerkiness in first few weeks driving my M4. It happened in 1st gear, Sequential mode, Sport/+, in city traffic where I couldn't properly put my foot down. My conclusion was that essentially you can't drive this car like a pussy in Sport/Sequential mode, being indecisive with the throttle. The car thinks you really want to go fast, but then you don't and it jerks. This seems to be consistent with what few people wrote here already, so I'm just sharing my experience. Who would have guessed that an M car actually takes some skill to drive . I think you just need to get used to it being different.