DCT M3 Or Manual M3?

[Tony B]

Originally Posted by ss134

Don't agree - i can shift from 6th to 3rd with 3 quick flicks of the left paddle almost instantly......or just plant the throttle fully and pull on the left paddle once and DCT will put me in the optimal gear and revs for max acceleration.

Read what I said - skip 1 gear (6 to 4) and what I said is true. skip 2 gears (6 to 3 for example) and it is completely different. The shift will not be quite as fast as 6 to 5 but there is no need for the intermediate gear.

Think about it - one clutch (B) handles gears 1 3 5 7 whilst the other clutch (A) handles 2 4 6. Whenever a gear is selected and in use, the system has pre-selected what it believes will be the next required gear, either + or - 1 relative to the gear you are in, with the respective clutch waiting to engage when you pull the paddle.

So in your 6 to 3 change, clutch A is active, with clutch B ready to engage either 5 or 7 depending on what the system believes you will need next. Pull the paddle 3 times (down) there will be a brief pause whilst the system changes the pre-selected gear to 3 and then clutch B engages as clutch A disengages.

Now think about what has to happen for 6 to 4, both of which have to use clutch B......

[Tony B]

Originally Posted by 335rocket

yeah I know that, Im saying 2 tenths of a sec faster due to quicker shifting, not actual power and acceleration

A DCT car does accelerate slightly quicker than a manual car, regardless of shift speeds, because it has slightly lower gearing, in gears 2 to 6 ( I think 1st gear is higher than the manual transmissions 1st gear for some reason). The faster shift speeds also have an influence too

[335rocket]

but what sucks is that its a 3k option?

[mkoesel]

Originally Posted by Tony B

Now think about what has to happen for 6 to 4, both of which have to use clutch B......

I can't understand the point you are trying to make. A shift from 6 to 4 will essentially happen just like it would with SMG or with a manual for that matter. Disengage clutch, disengage 4th gear, engage 6th gear, engage clutch.

Very simple.

The other clutch and output shaft needn't be involved with the shift at all. Now, its quite likely that there will be some activity on that shaft very soon after the shift from 6 to 4 completes, since the software will reassess which gear it predicts you will go to next (either 3rd or 5th now, rather than either 5th or 7th as it would have been when you were in 6th gear). But this is all secondary to the shift itself, and at no time must the other clutch be closed during the 6 to 4 shift.

[Tony B]

Originally Posted by mkoesel

I do see what you mean with respect to DCT, however I have to disagree with you. And, regarding the SMG transmission, I disagree that it uses an H pattern. I suppose you meant that it is a standard 6 speed manual transmission? If so, yes, I acknowledge that is true. But I don't think you understand that the DCT is also not a sequential manual (like found on a typical motorcycle) either. It can shift from any gear too any gear. In fact, we just recently had this discussion in another thread. Since we've gone OT quite a bit here, I will direct you there for further discussion (if you would):

http://www.m3post.com/forums/showthread.php?t=412453

I said a whole lot about this topic there that I don't want to repeat again. Now, if you read the thread you'll probably note that there is some speculation there too. However, much of what I said there can be backed up simply by trying these things IRL, which I have done.

And I agree with much/most of what you said there, especially on 30 July. It is definitely true that DCT is very smart, and overcomes many physical challenges by clever predictive algorithms. No amount of clever algorithms can overcome the physical inhibitors associated with the "skip one gear" situation. Try it, whilst watching the revcounter. I have tried this many times myself, most recently a couple of weeks ago, when I had a DCT loaner for a day, and was trying to convince myself that I did not want it, in preference to a 6MT.....

[mkoesel]

I do appreciate you reading the other thread. But, as I relate in my last post just above, I still don't see what the problem is with the 6 to 4 shift (or any other shift involving two even gears or two odd gears). Maybe I just don't understand what it is you are trying to point out about these types of shifts.

Originally Posted by Tony B

And I agree with much/most of what you said there, especially on 30 July. It is definitely true that DCT is very smart, and overcomes many physical challenges by clever predictive algorithms. No amount of clever algorithms can overcome the physical inhibitors associated with the "skip one gear" situation. Try it, whilst watching the revcounter. I have tried this many times myself, most recently a couple of weeks ago, when I had a DCT loaner for a day, and was trying to convince myself that I did not want it, in preference to a 6MT.....

[mkoesel]

Originally Posted by 335rocket

yeah I know that, Im saying 2 tenths of a sec faster due to quicker shifting, not actual power and acceleration

Not sure what you meant by that. What you essentially just said was that the car accelerates 2 tenth of second faster to 60mph, but its not due to acceleration. You are correct that both cars make the same power, of course.

Part of the process of accelerating in a car is the act of switching to the next ratio when the engine runs out of RPM in the current one. So, DCT absolutely does make acceleration faster. It shaves off some of the time it takes to switch gears with a manual transmission. There are also gearing differences between the two that could be a factor as well. I am actually not sure which puts down more wheel torque in 1st and 2nd gears (or other gear). I'm sure its somewhere on the forum though.

[Tony B]

Originally Posted by mkoesel

I do appreciate you reading the other thread. But, as I relate in my last post just above, I still don't see what the problem is with the 6 to 4 shift (or any other shift involving two even gears or two odd gears). Maybe I just don't understand what it is you are trying to point out about these types of shifts.

Oh it was a long time ago now and I am beginning to lose the point myself....what I was trying to say, was, whilst DCT is indeed quicker than SMG in almost all circumstances, when skipping one gear it is not. At best it does exactly the same thing as SMG ( de-clutches, changes ratio, re-engages the same clutch), or, as in my experience, it selects the intermediate ratio momentarily in order to maintain drive, then selects the ratio you have requested. In which case it is slower than SMG.

As I have never experienced a lack of drive torque - which you would expect if it does the SMG thing - and I have watched the revs pause at intermediate values in mid sequence during single gear skipped up/downshifts I have to conclude that it is selecting the intermediate gear in order to maintain drive torque. And it does make these changes notably slower than normal ones

Now - you have the opportunity to go out in your car and try it out, whilst I am relying on memories of numerous experiments that I have tried....so you have the advantage over me.

I do expect to be trying another car at the end of the month, and I might take a video with me this time!

[TailHappyM3]

Which one is faster is not necassarily which one is right for you. You'll never be able to get the very top performance out of either gearbox and feel the insignificant difference in performance so get what feels better for you after driving both. Sorry OP but these types of questions are really silly. What is most important is to get the correct gearbox for YOU.

I really don't care if the DCT was even .5 seconds faster because it's not my cup of tea.

[dimabimmer]

I can shift from 6th to 2nd in less than 1/4 of a second with my 6MT> can you beat that with your DCT?

I can rock my car out of snow bank very gently without burning clutch with my 6MT> can you do that with your DCT?

6MT> DCT

6MT FTW

[mkoesel]

Originally Posted by Tony B

Oh it was a long time ago now and I am beginning to lose the point myself....what I was trying to say, was, whilst DCT is indeed quicker than SMG in almost all circumstances, when skipping one gear it is not. At best it does exactly the same thing as SMG ( de-clutches, changes ratio, re-engages the same clutch),

This much I agree with you on. It is basically no faster than SMG at best (well in theory it could be a tiny bit faster since the hydraulic wet clutch might work faster than the SMG with its external hydraulics operating the dry clutch, but this is a minor nitpick). However, originally I believe you had said that SMG will be faster, which is why I chimed in.

or, as in my experience, it selects the intermediate ratio momentarily in order to maintain drive, then selects the ratio you have requested. In which case it is slower than SMG.

As I have never experienced a lack of drive torque - which you would expect if it does the SMG thing - and I have watched the revs pause at intermediate values in mid sequence during single gear skipped up/downshifts I have to conclude that it is selecting the intermediate gear in order to maintain drive torque. And it does make these changes notably slower than normal ones

Now - you have the opportunity to go out in your car and try it out, whilst I am relying on memories of numerous experiments that I have tried....so you have the advantage over me.

It's all dependent on just how fast you are able to pull the paddle. If you don't pull it extremely fast, I agree you'll get two gear changes. But that aside, the kickdown feature, which only requires one paddle pull, would certainly not engage intermediate gears.

I do agree SMG would be faster going straight from 6 to 4 than DCT would be going from 6 to 5 to 4. One thing that may very well be true is, because SMG is a slower system, it could be easier to get the double paddle pull in quick enough for it to register as one shift than it is with DCT.

[bruce.augenstein@comcast.]

Originally Posted by dimabimmer

I can shift from 6th to 2nd in less than 1/4 of a second with my 6MT> can you beat that with your DCT?...

I don't know how long it takes a DCT to shift from 6th to 2nd gear - but I know damned well you can't do it with your six speed in less than a quarter of a second.

No. Possible. Way.

Powershifting, say, the three-four, it it possible to get below a quarter of a second if you just dab the clutch - meaning no way do you get even close to the floor.

We measured this stuff maybe 20 years ago with an accelerometer (at a couple of hundred samples per second) hooked to a PC.

Downshifting while moving the lever forward, left and back is a much more time-consuming process, especially since you can't just dab the clutch in that venue.

[mkoesel]

Yes to all three. Though, I'd never actually do the middle one (if you want to read more about heal-toe and DCT, you'll find it via a forum search). Edit, looks like you deleted that part just before I clicked "quote".

Originally Posted by dimabimmer

I can shift from 6th to 2nd in less than 1/4 of a second with my 6MT> can you beat that with your DCT?

I can rock my car out of snow bank very gently without burning clutch with my 6MT> can you do that with your DCT?

6MT> DCT

6MT FTW

[Alex1911]

There have been a lot of these threads since I have followed/joined this forum, I think the OP should have used the search function.

I went with the 6MT, I'm somewhat happy, you'll want a clutch stop and the weighted knob. There are times I wish I had gotten the DCT.

I really enjoy the 6MT when I want to be driving... When I'm tired or irritable and I don't really want to be shifting, I miss the "automatic".

Yes, the DCT is obviously .2sec quicker, but the car is already plenty quick, .2sec quicker doesn't equal $2900 IMHO.

I see a lot more complaints about the DCT over the 6MT, I took that into account.

In the end, it comes down to your needs and your outlook. DD in bumper to bumper traffic, no brainer= DCT. Track the car a lot= DCT. Old School= 6MT. Enthusiastic about driving= 6MT. There is no right or wrong tranny, it's just want fits the driver's needs better... Just my opinion as someone who is a new'ish owner and went through the decision making process.

If I crashed my M3, I'd probably buy a new one with the DCT.

[captainaudio]

Just as a point of reference many race cars (including the racing version fo the M3) can not skip gears.

CA

[dimabimmer]

^^^^^

thats a good one! + 1000

[dimabimmer]

Originally Posted by captainaudio

Just as a point of reference many race cars (including the racing version fo the M3) can not skip gears.

CA

Here is a video to support your statement:

http://www.m3post.com/forums/showthr...+rock+practice

[mkoesel]

Originally Posted by captainaudio

Just as a point of reference many race cars (including the racing version fo the M3) can not skip gears.

CA

No doubt, absolutely. That's because they use sequential manual racing transmissions with straight cut gears and no syncros. Many have a clutch pedal for launching as well, like the M3 GT2. Like I said in the other thread I referenced, race cars don't really need multigear downshifts. You want the car in the power band all the time.

DCT is no race transmission, that's for sure. But it can probably shift as fast or faster than many of them.

[Voltigeur]

-

DCT faster. I chose MT for the involvement / challenge.

[Ctm309]

Originally Posted by mkoesel

Sure it does. Do you have the DCT in your car? If so, I can probably help you with an issues you might be having with multigear downshifts.

My DCT in D mode say in 6th about 45 or so and I accelerate it will drop into second gear! and that's without punching it. That is at level 3 and no sport.

[rzm3]

I've had both.

6MT had a pretty notchy/sluggish throw which I hated. Clutch pedal had long travel and somewhat vague engagement point.

Then I got the DCT. It's not perfect, but on city streets it shifts seamlessly, on the track you don't even think about shifting anymore.

DCT is the perfect match for the M3 because it makes the greatest all-around sports car in the world even smoother and faster.

[SenorFunkyPants]

Originally Posted by Alex1911

Enthusiastic about driving= 6MT.

Wrong.

Originally Posted by Alex1911

There is no right or wrong tranny, it's just want fits the driver's needs better.

Right.