DCT vs Manual - How Much Vehicle Speed Gained During Upshifts?

[CanAutM3]

Originally Posted by FTS

This is the core of the argument or focus to say it differently, you did nail it.

Originally Posted by FTS

However, there is another factor, one that you also mentioned: the speed advantage is continued and even increased after the shift.

As a tidbit, I believe it is the other way around, where the speed advantage is actually progressively decreased after the shift.

There is this common misconception that if you exit a corner 10mph faster, you carry that speed advantage for the entire duration of the straight. In reality it is not the case. Since a car accelerates less and less as its speed increases, it means that the car accelerates more when it travels at a lower speed, resulting in the 10mph progressively decreasing as the car travels down the straight. Further, since the car that exits the corner faster needs less time to travel the distance down the straight, it has less time at its disposal for acceleration. As an example, this phenomenon can be seen in a 1/4 mile where a run with a lousy 60ft usually yields a higher trap speed. I am sure you can see these observation looking at your data logs.

As another tidbit, the fact that when the car travels faster it needs to brake earlier does not hinder its advantage in any way. A car has a given deceleration slope when braking, so when it travels faster it needs to brakes earlier to match the speed at the point where it would start to brake when having a lower speed. In the section where the faster car has started to brake and the slower one hasn't, the former is still travelling faster than the later during that distance; hence covering the distance in less time.

BTW, I am just nitpicking for the sake of discussion

Originally Posted by FTS

I also wondered about this as well. At the tracks we visit, there are half a dozen corners taken between 45-50 mph (only one below 40 mph). So, I tried few different ways in those corners with 3rd vs. 2nd gear, keeping in mind the time it takes me to upshift from 2nd to 3rd. Again, this is in the GT3, so gearing and traction are quite different, but it points to show that we should not make assumptions, test and measure to see what works best.

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.

My point was much more simple, if you cannot take a corner at WOT in a higher gear, there is zero benefit in using a lower gear, no need for any more data .

However, as you pointed out, if the corner can be taken at WOT in the higher gear, a more in depth analysis is needed to understand if there is benefit in using a lower gear. That is where data is king .

[bigjae1976]

Originally Posted by CanAutM3

My E92 was a civic 2008 with EDC, but I don't think it makes any difference.

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...

C'mon...lift is not in my vocabulary...you know that!

I've been debating whether 2nd or 3rd is faster. My E46 M3 shifts like crap so I have to slide it gently into gear so I'm sure 3rd gear is faster. If I had a gearbox that did not have synchros hanging on by a thread...I would say going into 2nd and keep the revs up would be faster.

But in the E90, I think 2nd is faster because you can get the rear around with the throttle. And the penalty from an extra shift with the DCT is almost nothing.

I'll admit, I need to play with those corners more in the E90.

[FormulaMMM]

Here's some data I have on this. This was my tuned, full exhaust 6MT E90 vs a stock (power wise) E92 DCT on the back straight at my local track. Same day, conditions, etc. Power advantage had nearly pulled me even at the top of 3rd gear, then a 3 mph loss when I shifted into 4th.

(Speed disparity at the start of the straight -- coming out of a hairpin -- is his Clubsport vs stock EDC for me.)

[CanAutM3]

Originally Posted by FormulaMMM

Here's some data I have on this. This was my tuned, full exhaust 6MT E90 vs a stock (power wise) E92 DCT on the back straight at my local track. Same day, conditions, etc. Power advantage had nearly pulled me even at the top of 3rd gear, then a 3 mph loss when I shifted into 4th.

(Speed disparity at the start of the straight -- coming out of a hairpin -- is his Clubsport vs stock EDC for me.)

Real world data

Thanks for sharing

[bigjae1976]

I think I found out why my upshifts are a little rough in my E90. I reprogrammed my M Mode for a normal throttle setting, not power.

The shifts are smoother when it's in power. At least on the street.

[brian99997]

Here is my 997.1 GT3 6mt vs the M4 DCT, the top of each graph is G forces vs distance and the bottom is MPH vs distance.

The car on the right (M4) is making a 2nd-3rd gear, and 3rd-4th gear change during that section. The GT3 on the left is making a 3rd to 4th change only and takes around 159.3 feet at near 100mph before acceleration begins again or just around 900ms for the entire process. The M4 takes roughly 76.4 feet at 97mph or 450ms although I actually measured this on the 2nd-3rd shift because the 4th shift is hard to find quickly on the graph.

if nothing else, you can see the M4's curve is considerably smoother. I commonly shift into 3rd during corner exit at this point because the transmission is so gentle to the tires and doesn't upset the car coming off throttle as the manual does.

btw, the M4 was in sport plus engine mode with the S2 transmission setting.