[s.chan]

How "slow" is a steptronic compare to DCT? 335i

Steptronic is very quick in my mind but how quick is a DCT? 0.1s faster than a step?

what is the advantage of a DCT compare to a stepronic?

[tpipta]

There really is no comparison. Knowing the transmission differs from that of an M3, I absolutely love the DCT in the 135 and 335is. Instant shifts and no boost loss create for a much faster car.

Cheers,
Tony

[SilverII]

different tech....torque converter vs clutch

[s.chan]

Originally Posted by tpipta

There really is no comparison. Knowing the transmission differs from that of an M3, I absolutely love the DCT in the 135 and 335is. Instant shifts and no boost loss create for a much faster car.

Cheers,
Tony

So how much does dct quicker than steptronic?

[TroyDeJ]

i dont know times to give you but steptronic uses a torque converter so power is really transmitted through fluid motion. DTC has twin clutches so it doesnt slip as much and the shifts are much faster

[captainaudio]

Originally Posted by TroyDeJ

i dont know times to give you but steptronic uses a torque converter so power is really transmitted through fluid motion. DTC has twin clutches so it doesnt slip as much and the shifts are much faster

The torque converter on the 335i is locked up one the car gets moving (if I recall correctly it locks up at 10mph). At that point power is not transmitted via a fluid coupling and there is a direct mechanical correction between the engine and the drive wheels. Once in motion the two transmissions behave very similarly although the technology doing the shifting is very different.
The DCT will shift faster but the step will shift very quickly. The difference in shift times between the two is measured in milliseconds (to keep this in perspective the blink of an eye is about (200 milliseconds). Keep in mind that a car does not stop moving while it is shifting gears, it merely stops accelerating.

Bottom line is that the DCT is not a much faster car.

CA

[s.chan]

Originally Posted by captainaudio

The torque converter on the 335i is locked up one the car gets moving (if I recall correctly it locks up at 10mph). At that point power is not transmitted via a fluid coupling and there is a direct mechanical correction between the engine and the drive wheels. One in motion the two transmissions behave very similarly although the technology doing the shifting is very different.
The DCT will shift faster but the step will shift very quickly. The difference in shift times between the two is measured in milliseconds (to keep this in perspective the blink of an eye is about (200 milliseconds). Keep in mind that a car does not stop moving while it is shifting gears, it merely stops accelerating.

Bottom line is that the DCT is not a much faster car.

CA

thank you very much. it's very detail. what about a steptronic shift from 6 -> 3 or 4. does it has any delay? I think DCT wont face this problem, does it?

If steptronic is not alot slower than DCT, i will get a 335 N54 engine with steptronic.

[hmmcolor]

Originally Posted by captainaudio

Keep in mind that a car does not stop moving while it is shifting gears, it merely stops accelerating.

DCT does continue accelerating while it shifts. One gear is phased out as the other is phased in - there is never a time when no gear is engaged.

[captainaudio]

Originally Posted by hmmcolor

DCT does continue accelerating while it shifts. One gear is phased out as the other is phased in - there is never a time when no gear is engaged.

If that was the case with the DCT wouldn't that equate to a shift time of 0?

CA

[tofu-]

Originally Posted by captainaudio

The torque converter on the 335i is locked up one the car gets moving (if I recall correctly it locks up at 10mph). accelerating.

I keep reading diff things about the torque converter. I've heard about it locking up after first gear, locking up at certain throttle positions, locking up at certain rpm's, and now locking up at 10mph. What is the definitive answer?

[hmmcolor]

Originally Posted by tofu-

I keep reading diff things about the torque converter. I've heard about it locking up after first gear, locking up at certain throttle positions, locking up at certain rpm's, and now locking up at 10mph. What is the definitive answer?

I don't know any specifics for BMW, but the idea behind a locking torque converter is that it locks whenever it can (not shifting or at low speeds).

[captainaudio]

Originally Posted by s.chan

thank you very much. it's very detail. what about a steptronic shift from 6 -> 3 or 4. does it has any delay? I think DCT wont face this problem, does it?

If steptronic is not alot slower than DCT, i will get a 335 N54 engine with steptronic.

Since BMW does not make any model that is available with a choice of a Steptronic or a DCT it is not possible to make a direct comparison. What you could do that may give you a rough idea would be to compare a 335i DCT vs a 335i 6 Speed manual and a 335is DCT vs a 335is 6 speed manual

BMW published 0-60 times,

335is Manual 5.1
335is DCT 5.0

335i Manual 5.3
335i Step 5.5

So a Step is approx 4% slower than a manual and a DCT is about 2% faster than a manual 0-60.

This is assuming that BMWs published times are accurate, Also the DCT launch control feature (is this available in the IS) should give the DCT an advantage in 0-60 times. How this will relate in real world driving is another matter, In any case while the DCT will be faster than a Steptronic it will not be by a large amount.

According to ZF a Steptronic will shift in 200ms. I was incorrect a few posts back on the speed of a blink of an eye, The blink of an eye takes appox. 400ms.

CA

[TroyDeJ]

I believe the torgue converter locks when you put the car in sport rather then drive.

[mjollnir19]

from what i have read here DCT is the best and may even be better and a manual... but i never got a chance to try it out myself... to me though nothing is better than shifting the car on your own... double clutching and what not...

[captainaudio]

Originally Posted by TroyDeJ

I believe the torgue converter locks when you put the car in sport rather then drive.

Torque converter locks up at about 5MPH regardless of mode. At that point the torque converter is out of the picture and does not re-engage until the car slows down to almost a stop. It is not used for shifting grears as their are cluches on the planetary gear sets for that purpose.
Some of the newest versions of ATs use the conventional AT planetary gears for shifting but have replaced the torque converter with a mutli-plate wet clutch pack. Torque converters are very good devices for smooth starts but they are inefficient which is why modern ATs lcok them up once the car is under way. As both DCT and conventional ATs continue to develop they will likely reach a point where the performance will be virtually identical. The ZF transmission that BMW uses in the 335i is very similar to the unit that ZF suppplies for some very high performance cars inclusing the Jaguar XKR-S and the Maserati Grand Tourismo.



CA

[messi]

some useful explanations in this thread.

[Edward]

The E9x Steptronic is very fast, especially on hard acceleration upshifts.
The DCT is insanely quick on those very same shifts. Cant really explain what it feels/sounds like with words.
However in real terms, while the DCT is a lot quicker than a steptronic relative to the overall time frame we are talking about, in reality, the discussion of milliseconds is so quick anyways that it may be a totally moot point.
I'm a daily driver with my car so the best thing about the DCT for me is the sound of it.

Also, the new 650i 8 speed steptronic is digustingly fast. I'd say it's closer in shift speed to my DCT than to a 3 series steptronic 6 speed. The new 6 even makes the popping sound in between shifts that the IS as well as DSG equipped Audis make.

[Thud]

DCT has a huge advantage in shift speed, because it can "pre-shift" the next gear.

DCT also requires launch control in order to maintain the 0-60 times.
With a fluid-coupled torque converter, launch control isn't necessary, and you still get a 100% mechanical transfer once the converter locks up.

The new 8-speed steptronics are very close to the DCT in terms of shift speed, too.

[captainaudio]

Two different technologies that accomplish a similar function coming from two different directions. The AT is a convenience/comfort based design that has been tweaked for performance. The DCT is a performance oriented transmission that works well as a civilized daily driver, Each is very good at doing what the other excells at. The Step works quit well as a paddle shifted transmission and the DCT works well as an AT that can be put into drive and forgotten about.

As technology progresses they will likely become even closer and more and more indistinguishable.

If you are looking for that extra ounce of performance the DCT will be the better choice. If you are normally in "tranportation mode" and enjoy a spirited drive on the twisties the Step works very well.

I would venture to say that if the car is not being pushed very hard the average driver would be hard pressed to tell the difference.

CA

[BuddhaPilot]

Originally Posted by captainaudio

Since BMW does not make any model that is available with a choice of a Steptronic or a DCT it is not possible to make a direct comparison.

CA

I was about to say you're incorrect since the 135i is (was) available with all three. I just took a look at the configurator and noticed that for 2012, you can only get DCT or manual. That explains why pretty much every 2012 I've found in inventory has DCT, not that it's a much cheaper option than it used to be. I guess 2011 was the last year for the Steptronic in that car. Wonder if this is going to be a trend in the other series until the 8 speed auto is adapted?

[SteVTEC]

The biggest difference between the two is feel. There's very little difference in raw acceleration times. DCT should give you the nice crisp in-gear feel of a manual whereas the Step will still feel a little slushy due to the torque converter. I have the Step and it's probably the very best torque convertered automatic transmission I've ever had, but it's still not a manual transmission. If that's what you want, go either 6MT or the DCT. I'd have gotten the DCT if it was an option on the 335i, but BMW wants you to pay $7k extra for the 335is model to get that so I said no thanks.

[Edward]

Originally Posted by captainaudio

Two different technologies that accomplish a similar function coming from two different directions. The AT is a convenience/comfort based design that has been tweaked for performance. The DCT is a performance oriented transmission that works well as a civilized daily driver, Each is very good at doing what the other excells at. The Step works quit well as a paddle shifted transmission and the DCT works well as an AT that can be put into drive and forgotten about.

As technology progresses they will likely become even closer and more and more indistinguishable.

If you are looking for that extra ounce of performance the DCT will be the better choice. If you are normally in "tranportation mode" and enjoy a spirited drive on the twisties the Step works very well.

I would venture to say that if the car is not being pushed very hard the average driver would be hard pressed to tell the difference.

CA

I agree. In D mode, DCT is no better whatsoever than Steptronic. It may even be worse.