[demosthenes]

The purpose of this thread is NOT to start another 6AT vs 6MT war. There are plenty of threads on that already. There is no right or wrong choice. They are both great trannies, especially in the 335i.

The purpose of this thread is to understand the differences in how these two transmissions perform in an E90 335i. I've posed these questions on other threads but they were off-topic.

1a. If both cars had the same gearing and we punched them in 2nd gear at 3000 rpm (high enough for lock-up), would they feel and perform identically since the 6AT is locked up?
1b. Same as 1a given the 6AT's gearing advantage.
2. Does the 6AT lock up at 2500 RPM in all gears?
3. If both cars had the same gearing, which car would come off the line better if they were driven by a professional (the Stig)?
4. The 6AT has ~12% shorter gearing than the 6MT (3.46 vs 3.08 diff and similar gearing in 1st and 2nd gear), yet the 6MT is a little quicker 0-60. Why?
5. Are there any other important differences?

Here are the specs: http://www.bmwusa.com/Standard/Conte...fications.aspx.

If the 6MT comes off the line faster, it would explain the better 0-60 time. Since most of us spend little or no time racing or doing 0-60 runs, the answers to 1a and 1b are important because they shed some light on how these cars feel in normal driving.

Thanks.

[Angry3]

Originally Posted by demosthenes

The purpose of this thread is NOT to start another 6AT vs 6MT war. There are plenty of threads on that already. There is no right or wrong choice. They are both great trannies, especially in the 335i.

The purpose of this thread is to understand the differences in how these two transmissions perform in an E90 335i. I've posed these questions on other threads but they were off-topic.

1a. If both cars had the same gearing and we punched them in 2nd gear at 3000 rpm (high enough for lock-up), would they feel and perform identically since the 6AT is locked up?
1b. Same as 1a given the 6AT's gearing advantage.
2. Does the 6AT lock up at 2500 RPM in all gears?
3. If both cars had the same gearing, which car would come off the line better if they were driven by a professional (the Stig)?
4. The 6AT has ~12% shorter gearing than the 6MT (3.46 vs 3.08 diff and similar gearing in 1st and 2nd gear), yet the 6MT is a little quicker 0-60. Why?
5. Are there any other important differences?

Here are the specs: http://www.bmwusa.com/Standard/Conte...fications.aspx.

If the 6MT comes off the line faster, it would explain the better 0-60 time. Since most of us spend little or no time racing or doing 0-60 runs, the answers to 1a and 1b are important because they shed some light on how these cars feel in normal driving.

Thanks.

My .02 for what it's worth:

1a. I would expect so, the 6M car might pull slightly since it may have slightly lower parasitic losses.

1b. I doubt it, the Step has significantly shorter overall gearing in the lower gears and I expect would pull the 6M car from a roll at that RPM.

2. AFAIK yes.

3. Hypothetically a 6M car in expert hands with the Step transmission and rear end gearing should pull the Step car with an identically skilled driver. That's the benefit a drop-clutch launch and a major reason why 0-60 times are better for manual trans cars.

4. Having spent some time with 1 and 3-series cars with both transmissions I'm not convinced the 6M is faster. The only thing that shows that is the .1 second difference in BMW's published numbers, which of course don't reflect reality anyway. Car and Driver's best recorded 0-60 in a 335 test was a Step car by a similarly close margin. I think a 335 6M vs. a 335 Step identically specced out and prepped in identical conditions is absolutely a pure driver's race.

5. Not IMHO, once you get past all of the fanatacism for both setups you're left with 2 cars that are similarly capable and rewarding to own in their own different ways.

For reference, I have a 135 Step and have no regrets about going auto for the first time in 19 years of driving in 7 different cars. I had planned on buying a manual, but I was floored by the competence of the auto box and N54. The car just pulls like a mofo in the lower gears and is a blast around town. M mode is a ton of fun, and being able to putter along in D in Charlotte's ever worsening traffic is nice. That said it can't emulate the driver involvement of the 6M, and if I wasn't using the car for DD duty I might have gone that route. Since I am the Step was a perfect fit.

When it comes to the 6M or 6A debate there's just not a winner or loser IMO. Others may not agree.

[demosthenes]

Thanks Angry3.

Since the 6AT has significant shorter overall gearing in 1st-4th and the 6MT is probably better off the line, the 6AT might feel stronger in normal driving once the TC is locked up, right? That might explain why so many people love it.

[JayKay335i]

Originally Posted by demosthenes

Thanks Angry3.

Since the 6AT has significant shorter overall gearing in 1st-4th and the 6MT is probably better off the line, the 6AT might feel stronger in normal driving once the TC is locked up, right? That might explain why so many people love it.

I dont get the point of this thread?

There are plenty of #'s for both and its been shown that generally ATs are faster and it takes one hell of a driver, which 99% of the people on this forum arent, to be able to shift as quick or quicker than the steptronic transmission. MTs can drop the clutch, ATs can brake boost. The first questions are a moot point considering they dont have the same gearing.

Its been discussed a thousand times. Theres even a thread discussing the physics of the transmissions down to theoretical physics based calculations.

Also, arent the ATs different between 335s and 328s? The AT will perform better on the 335 than it will on the 328.

[demosthenes]

Originally Posted by JayKay335i

I dont get the point of this thread?

Most threads that talk about the 6AT and the 6MT turn into wars about which one is better or which one a "real enthusiast" would buy or which one shifts faster.

I've never seen a thread that talks about what's most important to most of us - which one responds better in everyday driving with light, medium and heavy throttle in a given gear?

For example, when the 6AT is locked up, does it really respond like a manual (no slippage, no lag, you can feel the direct connection between the engine and drive wheels)? If so, given it's gearing advantage, the 6AT would feel faster than a stick in normal driving. That's news to some folks. You certainly wouldn't expect it looking at BMW's published 0-60 times.

[JayKay335i]

Originally Posted by demosthenes

Most threads that talk about the 6AT and the 6MT turn into wars about which one is better or which one a "real enthusiast" would buy or which one shifts faster.

I've never seen a thread that talks about what's most important to most of us - which one responds better in everyday driving with light, medium and heavy throttle in a given gear?

For example, when the 6AT is locked up, does it really respond like a manual (no slippage, no lag, you can feel the direct connection between the engine and drive wheels)? If so, given it's gearing advantage, the 6AT would feel faster than a stick in normal driving. That's news to some folks. You certainly wouldn't expect it looking at BMW's published 0-60 times.

I gotcha. I would say that 95% of the time the car is in the RPM range that I want it to be in. Once in a while, as expected, if you let off the gas to slow down and then jump back on it real quick you'll get a hiccup. This will happen with any auto though. I'd say that the 6AT overall is a great setup and it certainly feels quicker than the 6MTs I've been in.

The thing is with how the 335 is programmed is that when the 6AT shifts it doesn't let out all its boost while the 6MT will dump all the boost while shifting. I know that Shiv addressed this in his latest versions of his tune where the car will now hold almost full boost while shifting. They're both great. I dont think you can go wrong with either one. It just comes down to preference IMHO.

Also, I think all the companies rate the 6MTs faster. Like was said before, they launch the sticks while just stepping on the gas on the AT.

[infinit9limi7]

ive been driving manuel all my life.. when i bought my 05 e46 m3 i decided to go SMG.. wow did i love it.. very responsive when upshifting felt faster when upshifting and rev matching is on point!.. ideal track car..

BUT..

when the 335i came out.. i just had to have TURBO once again.. i first hoped they would come out with SMG again.. but didnt.. soo i drove both manuel and steptronic..

steptronic first: im sorry to say that coming from SMG m3.. this felt cheap and straight auto like feeling w. tiptronic like any other car.. i even launched from a dig and redlined.. wow upshifting was sluggish!.. IMO wasn't fun to drive.. unpredictable.. i can imagine auto X the car would not work out.. and i didnt feel the torque..

6 MT: it pulls A LOT harder i felt way more control of the car.. and all i have to say is it felt more of a sports car that it is.. clutch was firm and very responsive (grabs low).. rev matching is effortless!!..

even driving my M3 SMG for 3 years. i admit i missed a manuel 6 speed..

well i bought a 6 speed 335i in late 07 bought an 08. and wow i never get bored of driving it at all.. i have a v3 tune.AA IC.Injen DCI.Agency Power catless DP's. Greddy Type-s bov.. and i'll tell you its running hard..

i just like the fact i can release the gear w. a press of the clutch.. and most of all im happy that i was able to find a 6speed locally w/o the wait!.

for those that have steptronic.. if you think that's great.. drive an SMG m3.. no comparison.. soo reason why i didnt buy one!.. thats all..

[Coolieman1220]

but i hear the SMG's arn't good when you're not beating them around town. is that true?

I bet you're waiting for a 335is?

[JayKay335i]

Originally Posted by infinit9limi7

ive been driving manuel all my life.. when i bought my 05 e46 m3 i decided to go SMG.. wow did i love it.. very responsive when upshifting felt faster when upshifting and rev matching is on point!.. ideal track car..

BUT..

when the 335i came out.. i just had to have TURBO once again.. i first hoped they would come out with SMG again.. but didnt.. soo i drove both manuel and steptronic..

steptronic first: im sorry to say that coming from SMG m3.. this felt cheap and straight auto like feeling w. tiptronic like any other car.. i even launched from a dig and redlined.. wow upshifting was sluggish!.. IMO wasn't fun to drive.. unpredictable.. i can imagine auto X the car would not work out.. and i didnt feel the torque..

6 MT: it pulls A LOT harder i felt way more control of the car.. and all i have to say is it felt more of a sports car that it is.. clutch was firm and very responsive (grabs low).. rev matching is effortless!!..

even driving my M3 SMG for 3 years. i admit i missed a manuel 6 speed..

well i bought a 6 speed 335i in late 07 bought an 08. and wow i never get bored of driving it at all.. i have a v3 tune.AA IC.Injen DCI.Agency Power catless DP's. Greddy Type-s bov.. and i'll tell you its running hard..

i just like the fact i can release the gear w. a press of the clutch.. and most of all im happy that i was able to find a 6speed locally w/o the wait!.

for those that have steptronic.. if you think that's great.. drive an SMG m3.. no comparison.. soo reason why i didnt buy one!.. thats all..

I think I can speak for just about everybody with an automatic transmission on the forum, nobody bought their car because it has "steptronic". Its old technology and is generally worthless. While some people may use it, its not exactly a selling point of the car. SMG and Steptronic are not similar, at all, except that gears are changed. The same goes for pulling like a truck. I've driven both. They pull the same.

[infinit9limi7]

Originally Posted by Coolieman1220

but i hear the SMG's arn't good when you're not beating them around town. is that true?

I bet you're waiting for a 335is?

i actually own both e46 m3 and 335i 6 speed.. and the m3 is my daily nowadays.. feels better on a day to day drive..when im lazy i just put it on auto and just let it do all the shifting haha.. and driving my 335i is pure enjoyment since its 6 speed w. all my mods..

[wuchao1]

Sorry if it sounds stupid...
But what does the AT locked up mean?
I dont know a lot about transmission...

[ctuna]

What about the control of torque in the corners that effects control, and how it
effects steering control and cornering ability.
Any comments ?

[Brey335i]

Originally Posted by wuchao1

Sorry if it sounds stupid...
But what does the AT locked up mean?
I dont know a lot about transmission...

It's when the AT behaved so badly, it got thrown in a cell for the night

[adrianBMW99]

I have the AT and I love it for everyday driving (the convenience was the deal breaker for me) but I do at times wish I got the MT. For some reason, to me a turbocharged car doesn't feel right with the AT, this applies to any turbo auto car, not just our step. At times, the auto is a bit jerky and hiccups in certain gears, in an MT, this would be fully controlled by me and I could rev as freely as I wanted to. In the case of the paddles with the AT, my personal opinion is that they are useless, they are always unpredictable in when the car will shift and I could see them confusing a driver on a track. Yes, in a drag race the AT would always be quicker, 99% of people will not be able to shift as quickly in an MT. I would be willing to bet that the opposite would be true on normal roads with traffic and plenty of turns.

[Weaselboy]

Originally Posted by wuchao1

Sorry if it sounds stupid...
But what does the AT locked up mean?
I dont know a lot about transmission...

Here is a good explanation of how a torque convertor works. Instead of a clutch to disconnect the engine from the drive train when the car is stopped, an auto trans uses a torque convertor.

Think of two fans facing one another. On the left the fan is connected to the engine and spinning around. The fan on the right is connected to the wheels of the car through the transmission and driveshaft. If the left fan spins fast enough it will cause the right fan to begin spinning. Get the idea? So now take those two fans and enclose them in a housing filled with oil and you have a torque convertor that sits at the front of an auto trans. When the engine spins the front part of the convertor fast enough, the rear part of the convertor will begin to spin also... moving the car.

Older cars had only the simple torque convertor process I described and going back to my fan analogy you can see how when applying more force to the powered fan there would be a little delay before all the force is applied to the drivetrain side of the fan. This sort of rubber band effect and slippage is overcome on modern cars by using a cog or clutch plate to lock the two sides of the convertor fans together after a certain RPM is reached. Once this lock occurs, there is a direct connection between the engine and transmission much like a manual shift car when the clutch is released.

The 335i AT for example locks up the torque convertor at 1,200 RPM, causing there to be very little difference in acceleration times between an auto trans vs. manual trans car.

[driverman]

Originally Posted by Weaselboy

The 335i AT for example locks up the torque converter at 1,200 RPM, causing there to be very little difference in acceleration times between an auto trans vs. manual trans car.

Then why does the 6AT in the 335i have a much lower rear axle ratio (3.46 vs 3.08) and similar tranny ratios in 1st, 2nd and 3rd and still have a slower 0-60 time (5.6 vs 5.4) (according to BMW web site for 335 sedan)?

Is it due to slippage in the torque converter? If so, when? During launch? During shifts? During hard acceleration while in 1st or 2nd?

[MazdaFan]

There is also a weight difference although in 335 it is very small, for a 328 the GM transmission weighs a ton compared to manual transmission.

PS fast shifting a manual transmission car for 0-60 or any kind of upshift is not that hard and I am sure much more than 1% of people on this board can get it right, down shifting and heel toeing is another matter of course. Personally I am still working on my heel toeing technique and fortunately the pedals in BMW are perfectly designed for this unlike in my Mazda3 where the gas pedal was too low for effective heel toeing.

[Weaselboy]

Originally Posted by driverman

Then why does the 6AT in the 335i have a much lower rear axle ratio (3.46 vs 3.08) and similar tranny ratios in 1st, 2nd and 3rd and still have a slower 0-60 time (5.6 vs 5.4) (according to BMW web site for 335 sedan)?

Is it due to slippage in the torque converter? If so, when? During launch? During shifts? During hard acceleration while in 1st or 2nd?

I would say it is due to higher internal frictional losses in the auto trans. If you look at a cross section of the auto trans, it is a pretty complex set of planetary gears to get all those ratios you have. A manual trans has a much more straightforward method of providing multiple gear ratios.

The torque convertor locks up at 1200 RPM and stays locked up, there would be no slippage from the torque convertor after the first few feet of acceleration in first gear.

[wuchao1]

Weaselboy thank you for the easy to understand explanation there!! So basically after the lock up the AT will transfer power just like a MT..... Got ya.

[captainaudio]

A few weeks ago I attended the BMW M-Power tour where we got to drive various M Cars, all with the DCT. During the presentation before we drove someone asked how the SMG compared to the DCT. The response of the BMW rep was "The SMG was Crap".

I concur. I drove an E46 M3 with the SMG and a Maserati GT with the Cabriocorsa, which was an SMG. I was not impressed.

CA

[captainaudio]

Originally Posted by JayKay335i

I think I can speak for just about everybody with an automatic transmission on the forum, nobody bought their car because it has "steptronic". Its old technology and is generally worthless. While some people may use it, its not exactly a selling point of the car. SMG and Steptronic are not similar, at all, except that gears are changed. The same goes for pulling like a truck. I've driven both. They pull the same.

You can't speak for just about anyone on the forum. I ordered my car with a Steptronic because I wanted a Steptronic and there are a lot of other people who did the same. I am very experienced with manual transmissions and have a conventional 4 speed in my track car. I also have a lot of experience in open wheel race cars with Sequential racing transmissions with manual clutches. When I bought the 335i I decided that after years of manual tranmissions I wanted to try an automatic. I do not remotely regret making that choice.

There is nothing old technology about the ZF Steptronic that is used in the 335i. It is a state of the art transmission. ZF intends to keep developing it and have stated that the feel that future Steprtonics will perform as well as DCTs. The next generation ZF Automatic, which is just beconing available will have a version that does not use a torque converter and will be equipped with a multi-plate clutch.

CA

[Tom K.]

Originally Posted by driverman

Then why does the 6AT in the 335i have a much lower rear axle ratio (3.46 vs 3.08) and similar tranny ratios in 1st, 2nd and 3rd and still have a slower 0-60 time (5.6 vs 5.4) (according to BMW web site for 335 sedan)?

The overall ratios (gear X rear axle) favor the auto by 15% in 1st, 9.5% in 2nd, 8% in 3rd and 07.5% in 4th. But 5th is 2.5% higher in the auto and 6th is a whopping 11% higher than the MT - so the 6 MT should pull harder in 5th and 6th if the auto is locked up. This would also explain the Steptronic's 2 mpg better EPA highway gas mileage rating.

When the 135i came out in 2008, BMW quoted a 5.1" 0~60 time for both MT and auto. Most magazine tests had the auto fractionally quicker at 4.6~4.7 and the stick at 4.8~4.9.

But BMW generally quotes the 6 MT as at least 1/2" faster to 60 for the 328i & 128i so apparently, the higher torque of the turbo helps mitigate the auto's slippage.

Tom