Disappointed with the F8X DCT specs

[CanAutM3]

I am hugely disappointed with the DCT specs on the F8X so far

That 89lb penalty is the first blow.

I also find that the gear ratios have been poorly selected for optimal acceleration performance. The DCT essentially has similar total ratio spacing as the 6MT between 1st and 6th, I even find that the ratios on the DCT are worse than on the 6MT . The lower gears have too much spacing while the higher gears are too tightly spaced to properly leverage the S55 power curve. 1st gear is so highly de-multiplied, that it will be impossible to put the power down. I think it was selected mostly to make the engine feel responsive in off boost puttering around. 7th is only an additional overdrive beyond 6th for fuel economy; having 7 gears is no longer used as an advantage for acceleration (tighter overall gear ratio spacing).

Looking at BMW published acceleration numbers (http://www.bmw.de/dam/brandBM/market...2975025706.pdf), the DCT has a 0.2s advantage over the 6MT from 0-100km/h. However, that 0.2s gap is maintained from 0-200km/h. I would have thought that the DCT quick shifts (2 more shifts needed to go from 100-200km/h) would have widened the gap. It seems that the lighter weight and/or better efficiency of the 6MT allow it too keep up with the DCT in that speed range.

Further, looking at the 80-120km/h pick-up numbers in 5th gear, the DCT is slower by 0.1s. Both cars have the same 5th gear overall ratio. Further, the 6MT matches the DCT 4th gear 80-120km/h despite the DCT having a slight gear ratio advantage in 4th. So I can only assume that the additional weight and losses of the DCT are the culprit.

We will have to wait for independent tests to confirm any of this. In the meantime, going with the numbers available to us, my feeling is that BMW went cheap on us for the DCT on the F8X .

[01ON19]

So get the manual. More fun anyway!

The time differences you refer to seem pretty small to me. I'm no engineer, but to say that "BMW went cheap" sounds off base to me since they could presumably choose any gear ratios they want.

[CanAutM3]

Originally Posted by Kanuck

So get the manual. More fun anyway!

The time differences you refer to seem pretty small to me. I'm no engineer, but to say that "BMW went cheap" sounds off base to me since they could presumably choose any gear ratios they want.

The DCT provided a very significant performance advantage on the E9X. I would have hoped for a similar advantage on the F8X.

I say they went cheap because they simply took the DCT directly off the F1X M5/6. Commonality reduces development and production costs.

My car doesn't start production until May, so I still have time to change my options. I may well go with the 6MT this time.

[JS919]

If BMW was only smart enough to hire you as a drivetrain engineer we would all be better off. They probably cheaped out and hired those crappy German engineers.

Just curious of the point you are trying to make on the ratios and and going cheap. Is it your understanding that there are certain gear ratios that cost more or less than others?

As far as acceleration numbers go. It is my understanding that the DCT transmission not only is heavier but also has more drag than the manual. The drag comes from the hydraulic system used to control the clutches.

I'm assuming the when BMW does acceleration runs to determine the published numbers they use a professional driver. That being said there would certainly be a bigger difference in acceleration between DCT and manual times with an average driver.

[mdss6]

Originally Posted by CanAutM3

I am hugely disappointed with the DCT specs on the F8X so far

That 89lb penalty is the first blow.

I also find that the gear ratios 7th is only an additional overdrive for fuel economy; having 7 gears is no longer used as an advantage for acceleration (tighter overall gear ratio spacing).

my feeling is that BMW went cheap on us for the DCT on the F8X .

Originally Posted by Kanuck

So get the manual. More fun anyway!

The time differences you refer to seem pretty small to me. I'm no engineer, but to say that "BMW went cheap" sounds off base to me since they could presumably choose any gear ratios they want.

My brother is fond of saying "different people are different." They sure are.

I, and some other non-buyers of the E90 M3, were sadly in that category because it was a gas guzzler. For me, there was no good excuse for this. A 4.0 liter gas guzzler when much more powerful 7.0 liter Corvettes, and 6.2 liter supercharged GT500s were not? Come on. Those cars too different to compare? How about the 5.0 liter Boss Mustang - similar weight and speed - but not a gas guzzler. And all because of the tightly compressed low gearing. Obviously you were a big fan of BMWs choice. I was not. And they have won at least one buyer by making what I think is a much better choice for 7th gear. I applaud the the ratios.

As for the extra mass of the DCT, I share a significant portion of your disappointment. But engineering decisions involve a series of tradeoffs. By using the more heavily built gearbox from the M5 I have every confidence it will never be a weak point in the M3/M4, almost no matter how much the engine is tuned up. I will be surprised if the M3/M4 can't reliably and durably launch off the line, as well as provide high end acceleration.

And as was noted, there is always the manual to answer your preference for lower mass and a shorter overdrive. It is always a better day when we have such choices instead of only being able to get it one way.

[elitex]

M5's DCT is simply awesome, much better than the E92 M3. Are you saying that it's going to cost significantly more money to change ratios? I don't think so but IDK enough about manufacturing costs.

[Carl L]

Originally Posted by CanAutM3

7th is only an additional overdrive for fuel economy; having 7 gears is no longer used as an advantage for acceleration (tighter overall gear ratio spacing).

No offense but I cannot believe you're moaning about this. I'm a "track guy" and can't once think of when I used 7th. The M3 may be track capable but it's a passenger car first and foremost- the tight 7th on the E9x DCT is utterly pointless.

[JS919]

In reference to the stated "very significant performance advantage on the E9X".

The following is from a Car & Driver test of the E92 M3 DCT.

"But Is It Quicker?

After scouring the test results for some useful conclusion, the answer is “not really.” The M DCT car hit 60 mph in 4.3 seconds, cleared the quarter-mile in 12.7 at 113 mph, and achieved 150 mph in 26 seconds flat. Compare that to the six-speed manual’s numbers of 4.3, 12.8 at 113, and 24.3, respectively. If you zoom in even closer and look at each 10-mph increment, the two cars trade off which is quicker until 120 mph, when the manual starts pulling away."

http://www.caranddriver.com/reviews/...quicker-page-2

[elitex]

Originally Posted by mdss6

My brother is fond of saying "different people are different." They sure are.

I, and some other non-buyers of the E90 M3, were sadly in that category because it was a gas guzzler. For me, there was no good excuse for this. A 4.0 liter gas guzzler when much more powerful 7.0 liter Corvettes, and 6.2 liter supercharged GT500s were not? Come on. Those cars too different to compare? How about the 5.0 liter Boss Mustang - similar weight and speed - but not a gas guzzler. And all because of the tightly compressed low gearing. Obviously you were a big fan of BMWs choice. I was not. And they have won at least one buyer by making what I think is a much better choice for 7th gear. I applaud the the ratios.

As for the extra mass of the DCT, I share a significant portion of your disappointment. But engineering decisions involve a series of tradeoffs. By using the more heavily built gearbox from the M5 I have every confidence it will never be a weak point in the M3/M4, almost no matter how much the engine is tuned up. I will be surprised if the M3/M4 can't reliably and durably launch off the line, as well as provide high end acceleration.

And as was noted, there is always the manual to answer your preference for lower mass and a shorter overdrive. It is always a better day when we have such choices instead of only being able to get it one way.

This bothers me a lot.

[/// M sa]

Get used to post like these until the car comes out. People are bored and act like engineers, once they drive all of this will go away. It's like off season in the NFL, us fans have nothing better to talk about except looks for bs out there.

[gee-m-w]

You should be able to drive an entire track in 4th gear this car. Drop to 3rd if you're being ridiculous but there's so much torque you don't technically have to.

[TheDeliverator]

Originally Posted by CanAutM3

I...I think it was selected mostly to make the engine feel responsive in off boost puttering around.

Interesting...

Do you recall the quotes from the BMW Engineer indicating the engine is so responsive that drivers not experienced with sharp throttle response may have issues. Perhaps it's in part due to the 1st gear ratio you've mentioned.

[CanAutM3]

Originally Posted by Carl L

No offense but I cannot believe you're moaning about this. I'm a "track guy" and can't once think of when I used 7th. The M3 may be track capable but it's a passenger car first and foremost- the tight 7th on the E9x DCT is utterly pointless.

I am not moaning about the long 7th gear. Like you, I never used 7th at the track. Most tracks I run need 2nd to 5th on my DCT E92 (I only use 6th on the back straight at WGI when the weather is cool enough). Now, those tracks will likely only use 2nd to 4th with the F8X.

What I deplore is that they have not leveraged the additional gear to tighten the ratios from 1st to 6th. They could have made 7th with a similar ratio (or slightly longer) as 6th on the 6MT with tighter gears in between.

[CanAutM3]

Originally Posted by //M sa

Get used to post like these until the car comes out. People are bored and act like engineers, once they drive all of this will go away. It's like off season in the NFL, us fans have nothing better to talk about except looks for bs out there.

I AM an engineer, it is probably why I overanalyze stuff like this

I checked the DCT option when I ordered my M4 without being fully convinced. I am now having 2nd thoughts.

[Alpine F31]

Originally Posted by CanAutM3

I checked the DCT option when I ordered my M4 without being fully convinced. I am now having 2nd thoughts.

Go back to the dealer and check the other box. 6MT. That's the box I'm checking. You've convinced me! Actually, my 8AT convinced me.

[Tonymiabmw]

Originally Posted by CanAutM3

I AM an engineer, it is probably why I overanalyze stuff like this

I checked the DCT option when I ordered my M4 without being fully convinced. I am now having 2nd thoughts.

Ratios are also based off power band of the car so I don't understand how you can say the ratios disappointing without driving the car or knowing characteristic of the cars engine.

[Sedan_Clan]

Originally Posted by Jonas

In reference to the stated "very significant performance advantage on the E9X".

The following is from a Car & Driver test of the E92 M3 DCT.

"But Is It Quicker?

After scouring the test results for some useful conclusion, the answer is “not really.” The M DCT car hit 60 mph in 4.3 seconds, cleared the quarter-mile in 12.7 at 113 mph, and achieved 150 mph in 26 seconds flat. Compare that to the six-speed manual’s numbers of 4.3, 12.8 at 113, and 24.3, respectively. If you zoom in even closer and look at each 10-mph increment, the two cars trade off which is quicker until 120 mph, when the manual starts pulling away."

http://www.caranddriver.com/reviews/...quicker-page-2

Nice find!

[gblansten]

I thought BMW was claiming the same 0-1000m time as the M5. If so the F8x with either the manual or DCT will be a beast.

CanAutM3 just get the DCT if that is what you want. I think it will work out ok.

[e46e92love]

Originally Posted by elitex

This bothers me a lot.

+10000.

These cars are NOTHING alike, and I don't want BMW trying to earn the customer who does, because that leads down the path to the dark side when these cars BECOME like those.

They are all great performance cars that are NOTHING alike. That is like saying all humans that weigh the same have the same BMI....

Cheers,
e46e92

[Racer20]

On the DCT, 1st gear is 17% shorter, 2nd is 12% shorter, and 3rd is 10% shorter.

I would guess that the wider spacing is less of an issue for the DCT due to less rpm drop between shifts, and the shorter gears of allow greater torque multiplication. The powerband of this car doesn't really require tighter spaced gearing, and given the cost of developing a new gearbox and fuel economy sacrifice, I'd guess it was an easy decision to use the M5 DCT.

Being an engineer, you should have some understanding of the trade-offs that go into designing and developing something as complex as a modern car, and to say that BMW "went cheap" because they didn't build the car exactly to your liking is a bit ridiculous.

I can appreciate the desire to analyze and optimize these kinds of things, but at the same time, you need to be realistic.

[SPACEMANRICK]

Originally Posted by Alpine F31

Go back to the dealer and check the other box. 6MT. That's the box I'm checking. You've convinced me! Actually, my 8AT convinced me.

I agree with you 100%, the 8 speed auto in my 2013 335 xdrive is fast, easy, and smooth but it sure is boring compared to my previous manual transmission BMW's....

[Tonymiabmw]

Originally Posted by SPACEMANRICK

I agree with you 100%, the 8 speed auto in my 2013 335 xdrive is fast, easy, and smooth but it sure is boring compared to my previous manual transmission BMW's....

Yeah but DCT doesn't feel even close to as sterile as a Automatic.