Stock gear ratios & final drive gearing

[JCtx]

I'd have liked a DCT differential on my 6MT for more relaxed cruising (with a minor reduction in acceleration), but am probably the only one .

[JCtx]

Originally Posted by PencilGeek

You're not the only one. That's exactly what I have right now...in the supercharged stroker.

That's great. Hey, what's your indicated speed at exactly 3K rpm? It's 72 mph stock in 6th. My numbers suggest 85 mph, but don't know if I did it right. That'd have been PERFECT to me but from the factory; am not going to spend on that. Take care.

[swamp2]

Originally Posted by gr8000

According to my calculations, the (theoretical) top speed at 8,400rpm for the stock 6MT and DCT is 302km/h and 321km/h respectively (assuming that the engine is allowed to rev up to the redline in the top gear on each car and assuming that it has enough power!).

If you really want the last bit of accuracy use the revs per mile calculation for tire size rather than the standard calculation:

Tire diameters are: std. calculation:
Without tolerances: [(265 x 0.4) x 2 + (18 x 2.54)] * pi = 2.10 m

Michelin website:
63,360 divided by revolutions pre mile = rolling circumference in inches:
For the 265/40ZR18 PS2 Michelin states 790 revs per mile so 63,360 / 790 = 80.202 inches = 2.037 m.

Also, you can add a drag calculation to get Vmax as well. The M3 is first limiter limited and if removed drag limited. The tricky part of getting a Vmax calculation correct is knowing drivetrain and tire losses. See my post here.

[pride355]

Originally Posted by gr8000

That's brilliant - thanks guys!!!

I just wanted these to calculate the speed of the 6MT & of the DCT at any given gear & engine rpm, which I did in an excel spreadsheet and seems to be working (I cross checked my findings for the 6MT with a couple of magazines that report top speed for each gear).

According to my calculations, the (theoretical) top speed at 8,400rpm for the stock 6MT and DCT is 302km/h and 321km/h respectively (assuming that the engine is allowed to rev up to the redline in the top gear on each car and assuming that it has enough power!).

For the first time BMW has a shorter gear ratios for 6 speed manual in its M cars:
E36 M3 EVO 6 speed with 3,23 diff and 0,87 6th gear ratio could do theoretical 330 km/h (roughly; I don't remember exactly)
E46 M3 6 speed and SMGII with 3,62 diff and 0,87 6th gear ratio could do theoretical 330 km/h (roughly; I don't remember exactly)
Now E9X M3 only do theoretical (probably real) 302 km/h (which is better than previous 6MT final drives in terms of performance since it is possible to hit 302 km/h with a de-limit M3 )

I had 3,64 Schnitzer shorter diff on my E36 M3 EVO coupe. I could hit the rev limiter in 6th gear, which was at 7600 rpm. It does 298 km/h real speed. (I'm talking about euro spec 321 hp M3 with full SS exhaust)

[pride355]

Originally Posted by gr8000

According to my calculations, the (theoretical) top speed at 8,400rpm for the stock 6MT and DCT is 302km/h and 321km/h respectively (assuming that the engine is allowed to rev up to the redline in the top gear on each car and assuming that it has enough power!).

If the charts located at this link http://www.m3post.com/forums/showpos...7&postcount=17 is at the rev limiter, then E9x M3 could do therotical 316 km/h in 6th gear; not 302 km/h which surprised me a lot when I first read it and responded immidiately with the above post.

This kind of therotical top speed (that is 302 km/) is really not BMW style.

[pride355]

Tall gear ratios of 3th - 4th and 5th gear used to bother me a lot when I had E36 and E46 M3s. On the other hand my 911 Carrera S had shorter 3th - 4th - 5th and 6th gears and only these gearings were enough to make the car faster than E46 M3.
Carrera S had a 308-309 km/h top speed in 6th gear at the rev limiter which was just perfect.

BMW used to have always 5 performance gears + over drive (in E36 M3 EVO, E46 M3, E46 M3 CSL, E39 M5)
Now, with the DKG, it has 6 performance gears + over drive and 6MT E9x is just in the middle; not too short not too tall.

[pride355]

Since 6MT will be revving higher in 6th gear, at lets say 180 mph, than DKG in 7th gear, stock vs. stock 6MT car would probably have higher top speed. (if we assume both cars are de-limited)

However from 70mph to 170mph, with gear ratios advantage, DKG equipped car would be faster than 6MT.

[pride355]

Here is a picture of my ex E46 M3, doing approx. 268 km/h (roughly 167 mph) @ approx. 7700 rpm WHICH means approx. 282 km/h (roughly 176 mph) @ 8100 rpm; in 5th gear.



BTW, I did 298 km/h ~186 mph in 6th gear (with the speedo error ) The Car had Superchips software and SS Race LTW exhaust.

[gr8000]

Originally Posted by pride355

If the charts located at this link http://www.m3post.com/forums/showpos...7&postcount=17 is at the rev limiter, then E9x M3 could do therotical 316 km/h in 6th gear; not 302 km/h which surprised me a lot when I first read it and responded immidiately with the above post.

This kind of therotical top speed (that is 302 km/) is really not BMW style.

The figures posted are an approximation of the true speed i.e. the 302km/h is my "desktop" approximation of the true top speed of a 6MT M3 (assuming no electronic speed limiter). Here is my methodology:



First I calculated the theoretical top speed following this:

Originally Posted by swamp2

Tire diameters are: std. calculation:
Without tolerances: [(265 x 0.4) x 2 + (18 x 2.54)] * pi = 2.10m

The theoretical top speed for the M3 I came up with based on the above (assuming 19" 265/35 tyre) is 315.4km/h for the 6MT and 335.4 for the DCT.



Then what I have done is to apply a 15% "tyre distorition factor" (which basically is a manual factor adjusting for tyre compression at higher speeds) in order to come to an approximated true top speed. The 15% figure came by comparing my theoretical speeds at redline for each gear of the DCT versus the actually measured true speeds for a stock DCT as these were measured by GPS equipment from a reliable Greek auto magazine. I was happy to see that my 15% correction factor was uniform accross all DCT gears and yielded the same true speeds as those measured by the magazine.

Then I applied the empirical 15% distortion factor to all gears of the 6MT.

The true top speeds I came up with are 302.3km/h for the 6MT and $321.4 for the DCT (assuming no electronic limitation).

[gr8000]

Originally Posted by swamp2

Also, you can add a drag calculation to get Vmax as well. The M3 is first limiter limited and if removed drag limited. The tricky part of getting a Vmax calculation correct is knowing drivetrain and tire losses. See my post here.

I have already done so. Based on 15% drivetrain losses and 10% tyre losses the theoretical Vmax I calculated is 301km/hr.



I would be helpful if I could upload my spreadsheet here but this forum does not offer this functionality yet...

[pride355]

Originally Posted by gr8000

The figures posted are an approximation of the true speed i.e. the 302km/h is my "desktop" approximation of the true top speed of a 6MT M3 (assuming no electronic speed limiter). Here is my methodology:



First I calculated the theoretical top speed following this:


The theoretical top speed for the M3 I came up with based on the above (assuming 19" 265/35 tyre) is 315.4km/h for the 6MT and 335.4 for the DCT.



Then what I have done is to apply a 15% "tyre distorition factor" (which basically is a manual factor adjusting for tyre compression at higher speeds) in order to come to an approximated true top speed. The 15% figure came by comparing my theoretical speeds at redline for each gear of the DCT versus the actually measured true speeds for a stock DCT as these were measured by GPS equipment from a reliable Greek auto magazine. I was happy to see that my 15% correction factor was uniform accross all DCT gears and yielded the same true speeds as those measured by the magazine.

Then I applied the empirical 15% distortion factor to all gears of the 6MT.

The true top speeds I came up with are 302.3km/h for the 6MT and $321.4 for the DCT (assuming no electronic limitation).

Interesting data
I was only refering to gear box - diff - tire diameter calculation..

[swamp2]

Originally Posted by gr8000

The figures posted are an approximation of the true speed i.e. the 302km/h is my "desktop" approximation of the true top speed of a 6MT M3 (assuming no electronic speed limiter). Here is my methodology:



First I calculated the theoretical top speed following this:


The theoretical top speed for the M3 I came up with based on the above (assuming 19" 265/35 tyre) is 315.4km/h for the 6MT and 335.4 for the DCT.


Then what I have done is to apply a 15% "tyre distorition factor" (which basically is a manual factor adjusting for tyre compression at higher speeds) in order to come to an approximated true top speed. The 15% figure came by comparing my theoretical speeds at redline for each gear of the DCT versus the actually measured true speeds for a stock DCT as these were measured by GPS equipment from a reliable Greek auto magazine. I was happy to see that my 15% correction factor was uniform accross all DCT gears and yielded the same true speeds as those measured by the magazine.

Then I applied the empirical 15% distortion factor to all gears of the 6MT.

The true top speeds I came up with are 302.3km/h for the 6MT and $321.4 for the DCT (assuming no electronic limitation).

Hmmm.. Not so sure about your method. The 15% drivetrain and 10% tire losses sound just about right. The 10% tire loss is speed dependent but at about 180-190 mph 10% is probably very close. The only other possible corrections are tire growth and indicated speed vs. true speed. I'm not so sure about the 15% empirical correction factor. Of course you must know tires expand at speed, not shrink.

Coincidentally our calculations (mine based solely on hp (with losses) and drag alone) agree quite closely. Your 302 km/hr is 187.6 mph, I get 186 mph.

[AreOut]

Originally Posted by elp_jc

I'd have liked a DCT differential on my 6MT for more relaxed cruising (with a minor reduction in acceleration), but am probably the only one .

you are not, I plan to put a ~10% longer final drive diff(so around 1:3.5) in a SCed M3, anyone knows if anything is available that would fit, maybe Dinan 3.45? Or would adding different ring&pinion be enough? I know that trick worked on E39 M5.

http://www.ebay.com/itm/BMW-m5-m3-25...ca98#vi-ilComp

would these from E34 M5 be OK?

[krx927]

Here is a link to nice tool on the German M forum:

http://www.m-forum.de/kalkulator/getriebe/index.html

[cmg5461]

Originally Posted by FStop7

6MT

1st: 4.055:1
2nd: 2.369:1
3rd: 1.582:1
4th: 1.192:1
5th: 1.000:1
6th: 0.872:1

Final Drive: 3.846:1

1st: 73:18
2nd: 45:19
3rd: 38:24
4th: 31:26
5th: 30:30
6th: 34:39

[Jesus E90 M3]

Originally Posted by AreOut

you are not, I plan to put a ~10% longer final drive diff(so around 1:3.5) in a SCed M3, anyone knows if anything is available that would fit, maybe Dinan 3.45? Or would adding different ring&pinion be enough? I know that trick worked on E39 M5.

http://www.ebay.com/itm/BMW-m5-m3-25...ca98#vi-ilComp

would these from E34 M5 be OK?

Mine is an DCT and i use it on highways daily i am looking for a more relaxed rpm and smooth drive, do you know any recommended gear ratio that i can go with. maybe 10% longer final drive?

[dparm]

I can't believe we're talking about gear ratios and no one has bothered talking about their relationship to power curves, which is called a thrust curve.

http://blackartdynamics.com/Transmis...hrustIndex.php


See my posts in page 2 of this thread:
http://www.m3post.com/forums/showthr...1029929&page=2

[kb9uwu]

Originally Posted by dparm

I can't believe we're talking about gear ratios and no one has bothered talking about their relationship to power curves, which is called a thrust curve.

http://blackartdynamics.com/Transmis...hrustIndex.php


See my posts in page 2 of this thread:
http://www.m3post.com/forums/showthr...1029929&page=2

well most of this discussion is over 6 years old... lets fire up the time machine.

[theBRUDDHA]

Originally Posted by gobuffs

MDCT
1-4.780
2-2.933
3-2.153
4-1.678
5-1.390
6-1.203
7-1.000

Final drive- 3.154

http://www.m3post.com/goodiesforyou/mdctinfo.PDF

So wouldn't this mean that the best gear for dyno pulls on DCT is 7th? But no one does 7th gear pulls....

[pbonsalb]

Most dyno operators don't want your wheels spinning that fast, but the 1:1 gear would be ideal. Its 5th on the 6MT cars, but I think most dyno in 4th. On my 5 speed E36M3, 1:1 is 5th but everyone dynos in 4th, which redlines around 125 mph.

[dparm]

Originally Posted by theBRUDDHA

So wouldn't this mean that the best gear for dyno pulls on DCT is 7th? But no one does 7th gear pulls....

You'd also hit the speed limiter way too early.