[Kbueno]

Originally Posted by scalbert

Having witnessed the many discussions and back and forth bantering, I thought I would run some numbers. This is also after having ridden in a 6AT this last weekend finally and realized the torque output seemed greater.

So to break it down, the 6AT has shorter gearing and will accelerate quicker even with greater drivetrain loss. From what we have gathered, the 6AT has only about 3% greater drivetrain loss. However, as shown by the below comparison, the gearing advantage is much greater.

Gear	6MT/6AT		MPH	MPH
1	86.67%		42	36
2	91.30%		70	64
3	92.53%		107	99
4	92.92%		142	132
5	102.32%		169	173
6	112.24%		194	218

Unless you are in 5th or 6th gear, the 6AT has an advantage. Just to clear the air, I have a 6MT and do not regret it. I just wanted to run the numbers to see what the real differences were. For those who have been around various vehicles are very aware that this is unusual for the automatic variant to have shorter gearing. But this is something a 3.50 rear end would fix for the 6MT.

Just FYI and as a simple comparison, the 6MT 335i has longer gearing than the C5 Z06.

Here we go again...where's the proof that the auto "accelerates quicker" Just because it has shorter gearing does not make it quicker. It's a damn good auto...for sure, but a race between an auto vs. manual would be a driver's race. I would think that the manual may begin to pull in the higher gears (less drivetrain loss), but that's my opinion.

[scalbert]

Originally Posted by 335lvr

Here we go again...where's the proof that the auto "accelerates quicker" Just because it has shorter gearing does not make it quicker. It's a damn good auto...for sure, but a race between an auto vs. manual would be a driver's race. I would think that the manual may begin to pull in the higher gears (less drivetrain loss), but that's my opinion.

Since both cars have the same wheels/tires and th gearing is obviously shorter in the 6AT; we can deduce the acceleration differences. Now comparing multiple dynos we can see the drivetrain loss differences which amounts to about 3%. There is more gearing advantage than drivetrain loss in the 6AT.

As mentioned, I have a manual but was curious about the real differences.

[dxb335d]

where did you get this information OP?

[scalbert]

Originally Posted by turbojet3

It would be interesting to see a MT car with a AT rear axle ratio.

Here is a comparison running the same rear end:

Gear	6MT/6AT		MPH	MPH
1	97.36%		37	36
2	102.56%		63	64
3	103.95%		95	99
4	104.39%		127	132
5	114.94%		151	173
6	126.09%		173	218

Except for 1st gear, the 6MT has shorter gearing and would be a handful in the lower gears.

[scalbert]

Originally Posted by dxb335d

where did you get this information OP?

The gearing numbers are on the BMW website. The rest is just math done in Excel.

[dxb335d]

cool, surely the auto will be slower to 100 due to needing to change up just before.

Do you have any info for the 335d?

[scalbert]

Originally Posted by dxb335d

cool, surely the auto will be slower to 100 due to needing to change up just before.

Do you have any info for the 335d?

In stock form and even moddified, I suspect the 6AT would have a slower trap speed than the 6MT due that additional gear change but ET may be better since more time is gained at the start where gearing advantage occurs.

I'll look up the 335d on a non-US site.

[335iheLLraiseR]

Originally Posted by turbojet3

It would be interesting to see a MT car with a AT rear axle ratio.

it hasn't been done by anyone yet, but one of the side effects would be that your DTC and/or cruise control would no longer work.

[scalbert]

Originally Posted by 335iheLLraiseR

it hasn't been done by anyone yet, but one of the side effects would be that your DTC and/or cruise control would no longer work.

Ya, I bet that would through a few alerts with the differences in frequencies.

In fact, I guess my car knew the type of discussions and threw a DCS Malfunction alert today. Now that is gone but it is telling me I need new pads. Oh well, I planned on taking it in for some minor items anyway. Might as well add this to the list.

[Kbueno]

Originally Posted by scalbert

Since both cars have the same wheels/tires and th gearing is obviously shorter in the 6AT; we can deduce the acceleration differences. Now comparing multiple dynos we can see the drivetrain loss differences which amounts to about 3%. There is more gearing advantage than drivetrain loss in the 6AT.

As mentioned, I have a manual but was curious about the real differences.

I'm still scepticle. With the variations we've seen with stock cars on dynos, how can you be sure it's 3%? I think where the auto shines is the shifting not the gearing. No way I can keep up with those fast shifts (I seem to have trouble in the 2nd to 3rd shift, makes me look like an ass sometimes).

[scalbert]

Originally Posted by 335lvr

I'm still scepticle. With the variations we've seen with stock cars on dynos, how can you be sure it's 3%? I think where the auto shines is the shifting not the gearing. No way I can keep up with those fast shifts (I seem to have trouble in the 2nd to 3rd shift, makes me look like an ass sometimes).

I wouldn't say the 3% is definitive. But it seems to be in the ballpark. But regardless, we know there is not a 10% difference which would wash out the gearing advantage.

[Lane]

These numbers do not mean much if we are talking about acceleration rather than theorethical speeds at red line. You should calculate the wheel torque (taking into account the AT drive train losses) at each speed in order to get the acceleration. Next you should define what is the wtq-limit between "traction limited" and "power limited" parts of the acceleration / wheel torque. Having non-DR's most of the gearing advantage is lost due not being able to get the wtq down.

Tuned MT = huge tq could do with even longer gears than stock. No need to have shorter gearing. Shorter gearing means just more wheel spin. Having slicks is another story.

[scalbert]

Originally Posted by Lane

These numbers do not mean much if we are talking about acceleration rather than theorethical speeds at red line. You should calculate the wheel torque (taking into account the AT drive train losses) at each speed in order to get the acceleration. Next you should define what is the wtq-limit between "traction limited" and "power limited" parts of the acceleration / wheel torque. Having non-DR's most of the gearing advantage is lost due not being able to get the wtq down.

Tuned MT = huge tq could do with even longer gears than stock. No need to have shorter gearing. Shorter gearing means just more wheel spin. Having slicks is another story.

It was a theoretical discussion.

But anyway, I have no problem with getting traction around here even with the RFT's and 386 WTQ on tap.

[scalbert]

Originally Posted by dxb335d

Do you have any info for the 335d?

I went to the BMW UK site and it did not list the gear ratios for the 335d.

But that comparison here would be moot as it is a significantly different engine.

[Lane]

Originally Posted by scalbert

It was a theoretical discussion.

But anyway, I have no problem with getting traction around here even with the RFT's and 386 WTQ on tap.

At 386 WTQ that takes good road and good driving. Nice starting point for some additional tuning

[scalbert]

Originally Posted by Lane

At 386 WTQ that takes good road and good driving. Nice starting point for some additional tuning

Well, the roads around here are pretty good as well as general fairly warm. No credit to the driver should be assumed.

[dxb335d]

thanks for trying bud, not alot in it acceleration wise 335i/335d!!


Carlos

[Insider]

Originally Posted by dxb335d

cool, surely the auto will be slower to 100 due to needing to change up just before.

Do you have any info for the 335d?

I found the following post from someone else on the internet:

Bit sad but I worked out the MPH/Thousand rev in each of the 6 gears on a 335d 6 speed auto..and speed at the max power point (4,400) & max revs (5,000).



6.46 - 28.4 - 32.3
11.51 50.7 - 57.6
17.71 77.9 - 88.6
23.58 103.7 - 117.9
31.08 136.8 - 155.4
39.00 171.6 - 195

[Evo8MRto335I]

You guys are fantastic, great info indeed. I had always being involved on testing my own previous cars mph/rpm on each gear calculations.

It does not take a rocket engineer to figure out why the Steptronic offered on the 335i is so competitive, the minor drivetrain loses, the fast shifting and the short gear ratios makes up for anything else and the top gear rpm is just a winner for gas savings.

my .2c

[Evo8MRto335I]

Originally Posted by LODOSS

I think the AT gearing is pure genius.

Aggressive 1-4 gears that will take care of almost all races and 5-6 for better gas mileage and also lower RPM = smoother cruises and less engine noise.

That is exactly what I am saying.. no more, no less

[dxb335d]

So in 6th a 335d could pull 195mph?

[JEllis]

More evidence that car makers are aggresively improving auto trannies....

Thanks for the info