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12-11-2014, 09:09 PM | #1 |
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DCT vs Manual - How Much Vehicle Speed Gained During Upshifts?
I am wondering how much speed difference can be expected between an upshift with the DCT vs. manual. I don't intend this question to be another "DCT vs. manual, which is better?" perspective, but more so as a technical question; does the DCT offer real and measurable speed advantage during upshifts? Of course there are benefits I see also on the downshifts, but for this discussion, I thought we just focus on upshifts.
For example, it generally takes me between 0.6 to 0.8 secs to do an upshift in a manual on the track, this is the time between throttle off and back on (WOT). Obviously the speed difference between the two methods will depend on beginning speed and accel G, but I thought may be someone may have more specific opinions and/or data on this. Hopefully it will be a positive, informative discussion |
12-11-2014, 09:17 PM | #2 |
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Doesn't the DCT shift in something like 80ms? That and there is effectively no throttle lift. The reason DCT cars are almost invariably faster in a straight line is faster shift speed and no throttle lift.
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12-11-2014, 09:27 PM | #3 |
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@gthal, if I remember what I read correctly couple of months ago, I think it is 100 ms in S3 and with minimal LatG load. Regardless it is certainly much faster than I can shift (at least half sec ). However, what does that mean in terms of actual speed, and also related to that what does that mean in terms of secs gained? I think the differences may be surprising.
As an example, the attached graph shows one instance in which I chose to shift from 3rd to 4th, and another instance which I stayed in 3rd, no shift, no throttle interruption (not a BMW). The difference in speed was nearly 8 mph, which I was not expecting. Last edited by FTS; 12-11-2014 at 09:32 PM.. |
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12-11-2014, 10:15 PM | #4 | |
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By no throttle lift, I assume you mean power shifting, where the engine inertia is recuperated to be converted in vehicle forward momentum. It is to be noted that this can also be done with a 6MT. On the E9X, the advantage was clear. I have done an analysis here on the the 6MT vs DCT on the E9X. The DCT gains about 0.2sec every time the 6MT needs to shift. Further, the DCT also benefited from tighter gearing to better exploit the power characteristics of the S65. While on track with my buddy that ran a 2012 ZCP 6MT E92 on the exact same tires and wheels as my civic 2008 E92, I have been repeatadly able to pull a clean pass on him on the back straight of our local track. When he would be behind me, I would just pull away. As much as I would like to claim that I am a better driver, I have to give that advantage to the DCT. Further, comparing data logs of my buddies C5 Z06, the slope of his speed curve (hence his acceleration) was clearly steeper than the one of my E92. Yet, we could also clearly see that every time he shifted, the M3 would catch up to enventually finish with a higher terminal speed at the end of the straight. Last edited by CanAutM3; 12-12-2014 at 10:36 AM.. |
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12-12-2014, 11:27 AM | #5 |
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There could be an additional advantage with the DCT in our S55 powered cars. Turbo lag is minimal, but we all know it's still there. The DCT may allow the turbos to remain spooled up and therefore experience less lag on upshifts.
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Road course laptimes for BMW M4 2015 6MT
WHP East Track: 1:04.880, Arizona Motorsports Park: 1:54.352 Road course laptimes for Porsche 911 991.1 GTS 7MT WHP East Track: 1:02.770, Arizona Motorsports Park: 1:48.889 |
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12-12-2014, 12:50 PM | #6 |
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I agree it is a valid point. However, I wonder with the S55 anti-lag wizardry, how much boost is actually lost on a 6MT shift. My understanding of the anti-lag is that it is to counter lost boost coming from quick throttle lifts, which is exactly what happens during a shift. That is probably what causes the "farting" sounds on lift-off and on shifts.
Last edited by CanAutM3; 12-12-2014 at 01:23 PM.. |
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12-14-2014, 12:03 PM | #7 |
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Although @MaynardZed has a valid point, let's ignore that for the argument, I think we'll find that impact as we collect data at the track.
When I look at the data I have from my previous NA car, the shifting that happened in the graph is at 97 mph. If we assume both runs were at the same speed, the version of the data corresponding to the run in which I did not shift gained 2.6 mph during the 0.8 secs it took me to shift. Ignoring the continued speed difference increase after the shift, the data analysis software shows that time gained only during this period was 0.031 secs. If I do manual calculation with approximations and taking average speed during that 0.8 sec time period, I come up with 0.026 secs. Either way it is not anywhere close to 0.2 secs per shift as @CanAutM3 calculated from his older thread, it is much smaller. Which is the reason I started this thread to see if I am missing something, because I would have believed at face value that "yes, 0.2 per shirt sounds about right." It may not be. Again, how this data will change for the F8x, I do not know, but I am looking forward to finding out |
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12-14-2014, 12:29 PM | #8 | |
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The 0.2 I reffer to is the time to speed difference. You are talking about time to distance. Which is not the same thing. Note that the benefit of the speed gained during the shift extends beyond the period of the shift itself. That extra "2.6mph" benefits for the entire acceleration period that follows the shift, not only the 0.8s duration of the shift. I used your 2.6mph here, but your graph seems to show a gain closer to ~5mph in those 0.8 seconds; don't forget that the MT car actually decelerates during that time (negative g on your chart). Going back to time to distance, in my E9X analysis, it shows the DCT crossing the ¼ mile mark 0.25 seconds faster than the 6MT. At 113mph, that is more than 40 feet, which is quite significant. Note that both "average" cars in my analysis are exactly matched from 0 to 40mph, so it is not a question of DCT launch control. Last edited by CanAutM3; 12-14-2014 at 03:38 PM.. |
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12-14-2014, 12:33 PM | #9 | |
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Newton's first law. An object in motion will stay in motion while the clutch is disengaged.
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Road course laptimes for BMW M4 2015 6MT
WHP East Track: 1:04.880, Arizona Motorsports Park: 1:54.352 Road course laptimes for Porsche 911 991.1 GTS 7MT WHP East Track: 1:02.770, Arizona Motorsports Park: 1:48.889 |
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12-14-2014, 01:49 PM | #10 | |
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So one cannot assume that a DCT lap will be faster by 0.2 seconds for every shift over a lap. Lap times are measured in time to distance, not time to speed. For example, three shifts are needed over the ¼ mile, but the DCT only has a 0.25 second advantage over the manual on that distance according to my analysis, not 0.6 seconds. That being said, the DCT clearly has an edge due to the (almost) instant shifts. I don't know how much it loses because of the additional weight and losses. I am looking forward for more data points on the F8X DCT and 6MT so we can do more analysis. Last edited by CanAutM3; 12-14-2014 at 02:28 PM.. |
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12-20-2014, 07:42 AM | #11 | |
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Faster shifting gains way more time than just the time saved shifting. |
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12-20-2014, 08:51 AM | #12 | |
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Yes, agree the turn into the straight is very important, but has nothing to do with upshifting. In fact, theoretically, the 6MT (being lighter) should have a better entrance speed into the straight (all other things being equal). In reality, its driver skill that determines entrance speed. This is anecdotal evidence of course, but another board member (his car is DCT) and myself (6MT) did the No Fly Zone AZ and our best 1/2 mile trap speeds were 144.8 (DCT) vs 144.5 (6MT). Unfortunately we did the event on different days so no head to head. I was powershifting, which I wouldn't typically do at an HDPE (unless passing maybe). On a road course maybe one of the biggest advantages of the DCT is consistency of the shifts since the 6MT guy will shift slower, even possible miss a shift every now and again. Hopefully the next NFZ AZ we can meet up on the same day and get some head to heads done for more evidence. I'm hearing maybe March they'll be back for another event.
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Road course laptimes for BMW M4 2015 6MT
WHP East Track: 1:04.880, Arizona Motorsports Park: 1:54.352 Road course laptimes for Porsche 911 991.1 GTS 7MT WHP East Track: 1:02.770, Arizona Motorsports Park: 1:48.889 |
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12-22-2014, 03:01 PM | #13 |
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Rightfully so.
My analysis on the E9X shows a 2~3mph gain for each shift in the lower gears regressing to a ~1mph advantage in the higher gears. It all depends on the track layout and how much distance there is on the straight after the shift (or shifts). That distance can be quite long. |
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01-07-2015, 08:40 PM | #14 |
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The gearing is also different so that has an effect. But a DCT up shift is a clear advantage over a manual up shift, at least on my E90. The DCT does a consistent power shift and the power feels continuous.
Where I think most people go wrong is they automatically think S6 is the fastest. I think whatever doesn't upset the car and allows you to stay on throttle is the fastest setting.
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01-10-2015, 10:15 AM | #15 | ||
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On the F8X, I also prefer the most aggressive S3 setting for the track for the same reasons as on the E9X . |
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01-10-2015, 04:19 PM | #16 | |||
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S6 could break the rear tires loose on an upshift in a turn. This would definitely affect when I could get on the gas. I found that S4 always resulted in a crisp but smooth upshift where I could be full throttle The downshifts are always smooth as silk.
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01-10-2015, 10:13 PM | #17 | |
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EDIT: Added link to youtube https://www.youtube.com/watch?v=p4IdVXetYrc Last edited by CanAutM3; 01-11-2015 at 10:06 AM.. |
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01-11-2015, 06:13 AM | #18 |
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Embedded video not working, but I totally believe it. My race mechanic, whose a very fast and accomplished driver, was disappointed with me that I got the 6MT instead of the DCT for my M4. I think his words were "DCT is the only car I've driven on the track that you can full throttle shift while in mid-turn and it won't upset the car."
No matter though, I don't let him drive my cars anymore. Makes me feel real slow watching him. I complained about some problem in my E36 at the track one time, so he takes it out on track and proceeds to pass everyone in advanced HDPE, comes back in and tells me there's nothing wrong with my car.
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Road course laptimes for BMW M4 2015 6MT
WHP East Track: 1:04.880, Arizona Motorsports Park: 1:54.352 Road course laptimes for Porsche 911 991.1 GTS 7MT WHP East Track: 1:02.770, Arizona Motorsports Park: 1:48.889 |
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01-11-2015, 09:00 AM | #19 | ||
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Basically it was most obvious in every 2nd gear corner where I'm at full throttle or pretty close. I know the rear suspension is on the bump stops (Dinan springs, OE shocks). So if I upshift in S5 or S6, the back end will kick out. Don't think it will cause the car to lose control but it definitely upsets it. Im pretty sure S6 would be much smoother if I did the turn in 3rd gear but those are 35-40mph turns. This leads me to believe it's an issue with my car. I've already had the dealer look at it a year ago and even took them on a 100mph run down an entrance ramp to show her...thought she was going to rip my door handle off! Normal function according to them.
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01-11-2015, 09:43 AM | #20 | ||
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Link to YouTube: https://www.youtube.com/watch?v=p4IdVXetYrc I agree, having the ability to up or downshift mid turn without upsetting the balance of the car is another benefit of DCT that can improve lap times. With my E46 I had to either short shift, ride the limiter or compromise my line in those corners at my home track. With my DCT E92, I could just hammer a perfectly smooth shift . Quote:
Last edited by CanAutM3; 01-11-2015 at 10:07 AM.. |
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01-11-2015, 09:48 AM | #21 | |
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Ensure you keep a steady throttle when you shift. If you lift, it will confuse the DCT logic. Just out of curiosity, can you take those 35-40mph turns at full throttle in 3rd. If not, there is no benefit taking them in 2nd... |
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01-11-2015, 11:22 AM | #22 | ||
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When you look at the difference in upshifting in itself without distance consideration, the gains realized are more substantial. However, when you factor in the 'distance' it is quite a different matter. The reason distance is important is because there is a finite distance to cover in a given lap, so even if you loose the speed advantage in manual shifting you are still covering the distance towards lap completion. When factored in, in the example I gave, the time advantage turns into 0.03 secs, far more less than actual time lost during upshift. However, there is another factor, one that you also mentioned: the speed advantage is continued and even increased after the shift. Unfortunately, due to distance covered by both scenarios, the braking zone is entered and the speed advantage is erased because the next corner is taken at about the same speed in both scenarios; the one with higher entry speed has to brake a little more Quote:
In 3rd gear full throttle is easy in those corners as long as the surface is smooth and traction can be maintained. In 2nd gear throttle modulation is necessary and acceleration is more violent, but nets an avg. time gain of between 0.6-0.8 secs; however staying in 3rd saves an upshift. Since my upshifts also take about the same amount of time, you would think it is a wash; however, because the matter at the core is time to distance and not time to speed, the net is really close to actual of 0.6-0.8 secs using 2nd gear in the corners I tried. So, in the example I gave earlier in the thread, which is Summit Point Main T1 through T4 (I did not show the entire set of graphs here), staying in 2nd gear through T1, shifting to 3rd in T2 and staying on it (running red line at 8500 RPM) and taking T3 near WOT after apex and entry to T4, nets a gain of nearly 1.2 secs in my findings and the way I drive; significant gains from 'normal' and assumed way of driving those corners, provided gearing allows it. Conclusion: Data is King! |
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