An Old DCT Lag Rant

[swamp2]

Originally Posted by sensi09

I get light surging from time to time coming to a stop. Always thought it was normal though

I am certain this is a distinct issue separate from the DCT lag issue.

[swamp2]

For all of the smart alecks chiming in with the useless "should have gotten a MT" and the corresponding +1's. You do realize that DCTs are basically the equivalent of 25-50 hp, depending on how you count and what contests you look at comparing the 6MT and M-DCT. There are plenty of good discussions here on the forum providing the evidence for this somewhat radical claim. Please keep your useless and snide comments to yourself and let us discuss the "pimple on the face of the supermodel" here. Our M-DCTs are an engineering and performance marvel.

[Frostbite]

I had the same dct lag issues when I first got my car. The dct update from the dealership helped but didn't completely solve the problem. I had OE tuning flash my dct when they did my ecu and that did the trick. I don't have any lag in D mode and the shifts are smoother & quicker in S. the dct flash also lowered my launch control to 4000rpm which makes a huge difference! I don't sit there just spinning my tires anymore lol.

You guys should consider a dct flash from one of the tuning companies. I think that'll be the solution to your problems

[Vic311]

Originally Posted by swamp2

For all of the smart alecks chiming in with the useless "should have gotten a MT" and the corresponding +1's. You do realize that DCTs are basically the equivalent of 25-50 hp, depending on how you count and what contests you look at comparing the 6MT and M-DCT. There are plenty of good discussions here on the forum providing the evidence for this somewhat radical claim. Please keep your useless and snide comments to yourself and let us discuss the "pimple on the face of the supermodel" here. Our M-DCTs are an engineering and performance marvel.

Really?

[quadpipes]

OK - to set the stage, I am talking about driving in 'S' mode and not automatic or 'D' mode.

I had an '09 E92 ///M3 and had a very noticeable lag when decelerating into a turn even when I had given the command to downshift. And if it was a left turn into traffic, it was very dangerous.

I now have an '11 E92 ///M3 - identical to my '09 except for ZCP - and there is no noticeable lag at all under the same conditions. There is a barely perceptible noise when the car is automatically downshifting (from S4 to S2) as I make a turn (yes, it does automatically downshift even in manual or 'S' mode), but this does not constitute a 'lag'. In fact it takes less time than would a manual (of which I own in other cars).

Don't know if this helps any. Good luck!

[swamp2]

Originally Posted by Vic311

Really?

Yes, really.

Try a search on the forum if you are curious. Many threads and posts, both from me and some others arriving at our conclusions using both simulation, formulas, testing and magazine results.

It comes down to shift time reduction. If you assume the DCT can shift in about 50-100 ms which is a very reasonable number supported by a large variety of evidence, along with the fact that a good MT shift is probably in the 0.4 s range, just do some simple math. You save about 0.6 seconds over two shifts in the quarter mile. The math really is that simple time saved shifting directly translates to just about the same time spent over a certain fixed distance. For a 3700 lb car use the basic formula for a 1/4 mi time:

ET = 6.1178 (weight/hp)^1/3 (ref:http://www.stealth316.com/2-calc-hp-et-mph.htm , weight in lb, hp obviously as hp)

And you will find almost a 63 hp requirement to have this much gain!

This is a very rough version, I don't think the difference is trult that large, it is however, quite significant, no matter from what source you draw your conclusions.

Bottom line, if you line up two M3 with equivalent drivers, tires, road, launch, weight, one with M-DCT and one without. The M-DCT car will very decisively pull on the 6MT car. There is even a big enough difference that the 6MT driver could be quite a bit better and the M-DCT would still have the advantage.

Similar advantages exist on a track due, especially when 3rd gear is used a lot, which on many track it is. There is 12% more torque to the wheels comparing both cars in 3rd gear simply because of the gear ratios.

back at ya...

[Vic311]

Speed of shifting isn't measured by units of power rather by milli-seconds..your formula is extrapolating data not measuring it.

Would you measure air temperature by air pressure units or speed/acceleration by units of weight?

You can choose to look at it this way, but to make a statement that a DCT is good for 25-50 hp is just silly.

Originally Posted by swamp2

Yes, really.

Try a search on the forum if you are curious. Many threads and posts, both from me and some others arriving at our conclusions using both simulation, formulas, testing and magazine results.

It comes down to shift time reduction. If you assume the DCT can shift in about 50-100 ms which is a very reasonable number supported by a large variety of evidence, along with the fact that a good MT shift is probably in the 0.4 s range, just do some simple math. You save about 0.6 seconds over two shifts in the quarter mile. The math really is that simple time saved shifting directly translates to just about the same time spent over a certain fixed distance. For a 3700 lb car use the basic formula for a 1/4 mi time:

ET = 6.1178 (weight/hp)^1/3 (ref:http://www.stealth316.com/2-calc-hp-et-mph.htm , weight in lb, hp obviously as hp)

And you will find almost a 63 hp requirement to have this much gain!

This is a very rough version, I don't think the difference is trult that large, it is however, quite significant, no matter from what source you draw your conclusions.

Bottom line, if you line up two M3 with equivalent drivers, tires, road, launch, weight, one with M-DCT and one without. The M-DCT car will very decisively pull on the 6MT car. There is even a big enough difference that the 6MT driver could be quite a bit better and the M-DCT would still have the advantage.

Similar advantages exist on a track due, especially when 3rd gear is used a lot, which on many track it is. There is 12% more torque to the wheels comparing both cars in 3rd gear simply because of the gear ratios.

back at ya...

[swamp2]

Originally Posted by Vic311

Speed of shifting isn't measured by units of power rather by milli-seconds..your formula is extrapolating data not measuring it.

Would you measure air temperature by air pressure units or speed/acceleration by units of weight?

You can choose to look at it this way, but to make a statement that a DCT is good for 25-50 hp is just silly.

I can see why you think this, but your reasoning is flawed.

Two points:

• Faster shifts make a car faster, period. The gain in a given contest is very likely close to the number of shifts multiplied by the time saved per shift.
• If a car is faster (at the same weight) one would typically conclude it has more power. In this case I have come up with an equivalent power that has the same effect as the gains from M-DCT related to its faster shifts. The amount of power does depend a bit on what contest you consider (0-60, 0-100, quarter mile, 30-160, etc.) hence why I posted a range.

Have a look at this very old and detailed post I made on this topic. This addresses the first point above. Pay particular attention to the graph. Again, there are also a PLETHORA of posts here on the forum on this idea of 25-50 hp, with plenty of PROOF of this statement. Please read up, don't make a fool out of yourself without reading those posts, both by me and other very credible forum members who have TESTED this in their supercharged M3s! Then perhaps begin your skepticism where some of these prior discussions have left off. I should refuse to continue this "debate" until you have taken this friendly and appropriate advise.

Last but not least, let's please start a new topic on this if you really do want to continue. We can keep this thread better on topic this way.

[SenorFunkyPants]

Originally Posted by swamp2

Medium, even speed, perhaps in the 40-60 mph range, gentle to medium (street level) braking, then followed by a medium throttle applied rapidly and immediately after letting off the brake. I've experienced lag which can be about 1 full second. The car simply feels as if it is completely ignoring the throttle application (and it really is)..

I know its stating the obvious....but if you are in D mode, decelerating, braking and reapplying the throttle then surely a significant number of times the reapplication of throttle will coincide with the DCT making a downshift (and thus a moment of throttle lock out)?

[ottoblotto]

Really? Again?
This will be a discussion my great grandkids will have...
*Both are great, btw...

[advans]

I think it really depends on your driving habits, or rather, style/use of driving.

If its a daily driver and you live in the burbs, I think a 6MT would def be the way to go. If you live in the city with constant traffic, the DCT would be great.

I ended up buying a DCT instead of a 6MT after driving a friends SMG M5, just loved how it felt and you still have the shifting capabilities.

It's really apples to oranges, it's one's taste.

[CSBM5]

Originally Posted by swamp2

Yes, really.

Try a search on the forum if you are curious. Many threads and posts, both from me and some others arriving at our conclusions using both simulation, formulas, testing and magazine results.

It comes down to shift time reduction. If you assume the DCT can shift in about 50-100 ms which is a very reasonable number supported by a large variety of evidence, along with the fact that a good MT shift is probably in the 0.4 s range, just do some simple math. You save about 0.6 seconds over two shifts in the quarter mile. The math really is that simple time saved shifting directly translates to just about the same time spent over a certain fixed distance. For a 3700 lb car use the basic formula for a 1/4 mi time:

ET = 6.1178 (weight/hp)^1/3 (ref:http://www.stealth316.com/2-calc-hp-et-mph.htm , weight in lb, hp obviously as hp)

And you will find almost a 63 hp requirement to have this much gain!

This is a very rough version, I don't think the difference is trult that large, it is however, quite significant, no matter from what source you draw your conclusions.

Bottom line, if you line up two M3 with equivalent drivers, tires, road, launch, weight, one with M-DCT and one without. The M-DCT car will very decisively pull on the 6MT car. There is even a big enough difference that the 6MT driver could be quite a bit better and the M-DCT would still have the advantage.

Similar advantages exist on a track due, especially when 3rd gear is used a lot, which on many track it is. There is 12% more torque to the wheels comparing both cars in 3rd gear simply because of the gear ratios.

back at ya...

A good manual driver will be way faster than 0.4 seconds. The 6MT is nowhere close to being 0.6 seconds slower in the 1/4 mile (when driven by a seriously competent driver that is ). The flip side of the coin is how well an experienced manual driver can nail a holeshot by being able to control the clutch to provide just the right amount of initial weight transfer coupled with just the right combo of clutch engagement versus throttle application for the conditions (tires, road surface, ambient temperature, etc). Said driver likely has down the ability to shift very quickly and would model in the range of 0.2 to 0.25 sec/shift.

As far as comparing torque to the wheels at any specific speed, realize that, just like differential ratio changes, when the shorter geared car has to upshift, the longer geared car is then putting down "more torque to the wheels" for the remainder of that gear until it has to upshift. It's not a clear cut choice as there are many variables including how the shorter geared car will require more shifts potentially over the measured distance (one reason why in something like comparing the E60 M5 6MT to SMG, the 6MT gains on the SMG car in the 1/4 due to one less shift required before the lights but it still just barely is behind in time at the end of course).

The problem with DCT is that the clutch engagement is an educated guess. It can't be anything but what was programmed into the system while an educated 6MT driver has an infinitely variable range of clutch modulation choices available to him/her. I think the ideal DCT setup would be to have a clutch pedal for daily maneuvering, parking lots, slowing down to make a 90 degree turn and then needing "just" the right amount of clutch engagement/throttle application, etc, etc.

[chris s]

Originally Posted by CSBM5

A good manual driver will be way faster than 0.4 seconds......Said driver likely has down the ability to shift very quickly and would model in the range of 0.2 to 0.25 sec/shift.

I'll just leave this here....

[US///M3]

If you can't master the art of rev-matching downshifts with perfect blips, the DCT is for ya...all you have to do like the passenger in the right seat is enjoy the sound and get your left foot out of the way.

[US///M3]

Originally Posted by swamp2

For all of the smart alecks chiming in with the useless "should have gotten a MT" and the corresponding +1's. You do realize that DCTs are basically the equivalent of 25-50 hp, depending on how you count and what contests you look at comparing the 6MT and M-DCT. There are plenty of good discussions here on the forum providing the evidence for this somewhat radical claim. Please keep your useless and snide comments to yourself and let us discuss the "pimple on the face of the supermodel" here. Our M-DCTs are an engineering and performance marvel.

In a straight line and from a standing start,maybe. On the track (race track) there isnt much advantage....
If you want a BMW for the dragstrip,get the 135i with an auto.

[CSBM5]

Originally Posted by chris s

I'll just leave this here....

Sure, why refute decades of drag racing experience? The tighter you are on the light the more likely the tighter you are on your shifts. You do realize there is a long history of shift speed time analysis in the drag racing world dating back 40+ years...

[SenorFunkyPants]

Except loads of M3 MT drivers on here can't even manage a shift into second without crunching the gears - imagine what damage they could do on a dragstrip.
But lets say .25 of a sec for an MT shift...given that the DCT S6 powershift is just a few ms an MT car is still losing 0.25 sec per shift.
You'll need a lot of extra HP to pull back .5 sec over 2 shifts

[CSBM5]

Yeah no doubt but of course that's not the fault of the car. Clearly to maximize the performance of the 6MT you have to have a *LOT* more experience driving a manual, launching technique, shifting technique, etc, especially if you expect to provide mechanical respect to the drivetrain.

My point up above was that the 6MT is nowhere close to 0.6 seconds slower in the 1/4 mile as long as we assume purely competent drivers in each car. After all it takes a good bit of experience launching the DCT car to minimize its 60ft time too as it's somewhat difficult to manage that extremely brief period of initial weight transfer which is so critical to a good launch.

I think we agree on far more than we disagree here with respect to 6MT/DCT. Is DCT faster through the gears? Yep. Is it 0.6 seconds faster in the 1/4? No chance. Up to license losing and potential jail time (in some jurisdictions) is there a huge difference in performance? Not really, unless you consider a couple of tenths of a second advantage (again, assuming very competent 6MT driver here) from 2 shifts a make or break deal. Is DCT an awesome accomplishment by BMW and a freaking blast to run up through the gears? ABSOLUTELY!

I'd be glad to drive my 6MT at the strip up against a similar (and completely stock) 2011 DCT. I'll buy the rear tires, fresh, identical. We'll race for pink slips but I'll get that 0.6 second claim spotted to me.

Regards,
Chuck

[CSBM5]

Originally Posted by SenorFunkyPants

Except loads of M3 MT drivers on here can't even manage a shift into second without crunching the gears - imagine what damage they could do on a dragstrip.
But lets say .25 of a sec for an MT shift...given that the DCT S6 powershift is just a few ms an MT car is still losing 0.25 sec per shift.
You'll need a lot of extra HP to pull back .5 sec over 2 shifts

Nope, DCT doesn't shift instantly. It takes about 0.15 seconds (150 milliseconds) in S6, so it will lose (gain) about 0.1 at most per shift against a real 6MT driver.

[SenorFunkyPants]

Interestingly BMW 0-62mph figures puts the DCT 0.2 secs faster than the MT.

[SenorFunkyPants]

Originally Posted by CSBM5

Nope, DCT doesn't shift instantly. It takes about 0.15 seconds (150 milliseconds) in S6, so it will lose (gain) about 0.1 at most per shift against a real 6MT driver.

Actually the shift is 0ms as the next gear is pre-engaged...any time is for the clutch change which is essentially seamless.

[CSBM5]

Originally Posted by SenorFunkyPants

Interestingly BMW 0-62mph figures puts the DCT 0.2 secs faster than the MT.

Yep, but that could just as easily be 0.155 rounded, who knows? They probably aren't speed shifting the 6MT either. Without knowledge of the test and granularity of the time measured, we have no idea. Maybe they do have a good 6MT driver who nailed the launch and beat the DCT to the 60' time but then shifted like "BMW would expect" a typical driver to shift. We have no clue.