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      01-11-2009, 02:23 PM   #1
M3-Mike
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Gear Ratios: MT6 vs DCT

Here is a quick Excel I made up comparing the MT6 gear ratios to the DCT ones. Interestingly the MT6 has a lower 1st and top gear, meaning more torque when pulling away in 1st, and more engine RPM required at top gear cruise. I would almost have expected the DCT to have a lower 1st and yes a higher top gear given the fact that it has an extra gear to take advantage of.

See if my calculations make sense... I've attached the actual Excel sheet if you guys want to play with the numbers yourself.
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File Type: pdf 2008 BMW M3 - Gear Ratios.pdf (8.9 KB, 531 views)
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File Type: zip 2008 BMW M3 - Gear Ratios.zip (6.6 KB, 115 views)

Last edited by M3-Mike; 01-13-2009 at 11:34 PM.
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      01-11-2009, 06:32 PM   #2
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Quote:
Originally Posted by M3-Mike View Post
Here is a quick Excel I made up comparing the MT6 gear ratios to the DCT ones. Interestingly the MT6 has a lower 1st and top gear, meaning more torque when pulling away in 1st, and more engine RPM required at top gear cruise. I would almost have expected the DCT to have a lower 1st and yes a higher top gear given the fact that it has an extra gear to take advantage of.

See if my calculations make sense and I can upload the actual Excel sheet if you guys want to play with the numbers yourself.
Here is my spreadsheet calculating the theoretical car speeds for any given gear and engine rpm. Feel free to fiddle arround with it!
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File Type: zip M3 gearing.zip (3.2 KB, 150 views)
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      01-11-2009, 06:42 PM   #3
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I don't know why the zip file doesn't work... it is not corrupted in my desktop but when I try to open it from the thread it doesn' work! Any ideas as to how I can upload an excel sheet?

Why aren't we allowed to upload excels in the threads in the first place by the way?
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      01-11-2009, 08:44 PM   #4
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According to the spreadsheat the DCT doesn't have a true overdrive gear, i feel as though this can't be correct?

5-6-7 Gears seem horribly geared on the DCT, i would like to hear a BMW engineers explanation on the entire gearing of DCT with its 7 gears, seems they are not utilizing all 7 gears very well.
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      01-11-2009, 08:57 PM   #5
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Quote:
Originally Posted by M3-Mike View Post
Here is a quick Excel I made up comparing the MT6 gear ratios to the DCT ones. Interestingly the MT6 has a lower 1st and top gear, meaning more torque when pulling away in 1st, and more engine RPM required at top gear cruise. I would almost have expected the DCT to have a lower 1st and yes a higher top gear given the fact that it has an extra gear to take advantage of.

See if my calculations make sense and I can upload the actual Excel sheet if you guys want to play with the numbers yourself.
thks for the pdf file Mike

Ive saved it and very usefull
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      01-11-2009, 09:32 PM   #6
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Quote:
Originally Posted by Richie18 View Post
According to the spreadsheat the DCT doesn't have a true overdrive gear, i feel as though this can't be correct?

5-6-7 Gears seem horribly geared on the DCT, i would like to hear a BMW engineers explanation on the entire gearing of DCT with its 7 gears, seems they are not utilizing all 7 gears very well.
Yes, there is no reduction in 7th. Since the final drive is taller (numerically lower) in the DCT car, actual gearing in 7th is still taller than the OD 6th in the MT6.

What are the issues you see in 5-6-7?
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      01-11-2009, 09:43 PM   #7
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Here's a graph comparing the two in terms of acceleration at the wheels, taking into account weight and drag. Dyno data used from www.rri.se...

:edit: The horizontal axis is vehicle speed in km/h


Last edited by mixja; 01-12-2009 at 12:52 AM.
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      01-12-2009, 07:23 PM   #8
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Quote:
Originally Posted by Ronin13 View Post
Yes, there is no reduction in 7th. Since the final drive is taller (numerically lower) in the DCT car, actual gearing in 7th is still taller than the OD 6th in the MT6.

What are the issues you see in 5-6-7?
I had a miscalculation when browsing the total gear reduction between the final gears in the 6mt and DCT that led me to think that the DCT had a lower gearing.

It just appears to me that gears 5-6-7 seem very closely spaced when 6 and 7 are highway gears. As far as i know the M3 reaches top speed in 5th gear?

I know the V8 doesn't pack low end torque to be able to cruise at 2000 rpms like a Corvette can, but it doesn't mean you should have to cruise at 3000rpm's when there is an extra 7th gear.

Either way i would be interested to hear why they went with lower gearing in the tranny vs. a lower final drive ratio. From what i remember hearing you get the best power delivery when the transmission is at is at 1:1, the DCT would never get to benefit from what.
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      01-12-2009, 08:47 PM   #9
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Mixja, is that graph telling us that the MT car accelerates better in first and seventh gears, and the DCT in 3rd, 4th and 5th?

What is the basis of this data?

On acceleration runs in 2nd, 3rd and 4th, my DCT coupe was a fraction behind a MT saloon (see Drivers Republic online magazine for details and video).
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      01-13-2009, 01:32 AM   #10
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Quote:
Originally Posted by waremark View Post
Mixja, is that graph telling us that the MT car accelerates better in first and seventh gears, and the DCT in 3rd, 4th and 5th?

What is the basis of this data?

On acceleration runs in 2nd, 3rd and 4th, my DCT coupe was a fraction behind a MT saloon (see Drivers Republic online magazine for details and video).
Assuming every else is equal, the MT accelerates better in 1st, and in 6th accelerates better than the DCT 7th gear...

Basis of the data is chassis dyno data and weight/wheel data from www.rri.se, adding an extra 25kg for the DCT. Drag is based upon a Cd of 0.31 and frontal area of 23.58 sqft (found these figures via Google search)...

Again, assuming every else is equal, on a rolling start in 2nd gear from 50km/h - 250km/h, the DCT should win but not by a huge margin.

Of course, in the real world every engine is different, so it wouldn't be surprising if a strong engine in an MT M3 would beat a weaker engine in a DCT M3. If for example the DCT power falls away a bit at high RPM but the MT power is a bit stronger at high RPM, the periods where the DCT has an advantage are much reduced, meaning the MT would win...

Then of course there is the question of whether there is higher transmission loss with the DCT vs the MT...

Anyway, if you want to beat that MT saloon, a Dinan 3.62 diff is the trick - the graph below explains
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      01-13-2009, 09:47 AM   #11
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Quote:
Originally Posted by mixja View Post
Here's a graph comparing the two in terms of acceleration at the wheels, taking into account weight and drag. Dyno data used from www.rri.se...

:edit: The horizontal axis is vehicle speed in km/h
Thanks, that's a nice chart! I'm not too concerned about launching from a standstill, and that is really the only time the MT6 has an advantage. From your chart it looks like 2nd gear is pretty equal in both cars, and then the DCT 3,4,5 give you some nice ratios between the MT6's 2, 3 & 4. I mostly drive on twisty back roads and having a stong gear in the 80km/h to 120km/h range is important. The DCT gear 3 seems to have nice power from 50km/h up to 130km/h and looks like a sweet gear for me, with 2nd available for hairpin turns, and 4th available on the straights. An MT6 drive would have to dip into 2nd more often around 60km/h. Speeds over 120km/h don't interest me too much as I prefer to keep my license and hey.. anyone can drive fast in a straight line.
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      01-13-2009, 09:57 AM   #12
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Since the M3 has more hp than torque and looking at the numbers and specs only , I would definitely argue that the MT will be quicker.

I have a question though--on your pdf, it states that the top gear with the DCT is 1.000 when 6th is 1.203.
Is this a typo?

I'm also surprised that the DCT doesn't have an overdrive.
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      01-13-2009, 08:50 PM   #13
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Quote:
Originally Posted by PencilGeek View Post
Are people really getting caught up in the term "overdrive" -- and thinking it actually means something that is useful to them? It's completely irrelevant. Your gears go through the final drive ratio anyways. So whether you have a 1:1 through 3.15 FDR, or a 0.87:1 ("Overdrive) through a 3.62 FDR they are exactly the same overall ratio because of the final drive ratio multiplier. (1.0 x 3.15 = 3.15, 0.87 x 3.62 = 3.15)
I Agree. Just to clarify though, the final drive on the MT6 is 3.846 and not 3.62 (perhaps you were just using 3.62 as an example)... so the MT6 actually revs higher in top gear compared to the a DCT equipped car.
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      01-13-2009, 08:55 PM   #14
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Originally Posted by Mr. 5 View Post
Since the M3 has more hp than torque and looking at the numbers and specs only , I would definitely argue that the MT will be quicker.

I have a question though--on your pdf, it states that the top gear with the DCT is 1.000 when 6th is 1.203.
Is this a typo?

I'm also surprised that the DCT doesn't have an overdrive.
I got my ratios from page 16 of the attached document. On page 17 it states that the MT6 will accelerate 0-100km/h in 4.8sec while the DCT does it in only 4.6sec. Now this might be simple because of the faster shifts, but I would also suspect having a lower 2nd gear helps sling the car to 100km/h a bit faster. 3rd probably would not come into play as the car will easily do 100km/h in second.
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      01-13-2009, 11:48 PM   #15
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Quote:
Originally Posted by gr8000 View Post
Here is my spreadsheet calculating the theoretical car speeds for any given gear and engine rpm. Feel free to fiddle arround with it!
Cool, thanks! I get slightly different numbers at the same 8400RPM.. I assume because of your tyre compensation factor? What is this 13-15% for?
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      01-14-2013, 03:09 PM   #16
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Quote:
Originally Posted by M3-Mike View Post
Here is a quick Excel I made up comparing the MT6 gear ratios to the DCT ones. Interestingly the MT6 has a lower 1st and top gear, meaning more torque when pulling away in 1st, and more engine RPM required at top gear cruise. I would almost have expected the DCT to have a lower 1st and yes a higher top gear given the fact that it has an extra gear to take advantage of.

See if my calculations make sense... I've attached the actual Excel sheet if you guys want to play with the numbers yourself.
Thank´s for the exel! Both of you!

one question... has anyone of you modified the gearing and/or final drive??

I would like to modify my 7:t gear instead of changing the final drive, then I can have all the fun AND good mileage...(Insane prices here in Sweden )

played around with the exel and found that 7:t with 0,500 =1500rpm @ 130km/h a perfect cruising speed...
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