Newbie seeking advice

[Heden]

Having owned a regular A6 3.0 TDi with S-tronic before, the one thing I miss from that gearbox is the ability to bypass gears when downshifting. The 8-speed in the RS6 must go through them one by one. It is also not as smooth as say the ZF8 I had in the X5. If you want the gearbox to be really jerky, just put it into sport and try driving like a normal person around town.

[W8PMC]

It might feel it Paul & perhaps the smoothness is masking the shift time, but believe me their is a noticeable difference, albeit in the grand scheme of things hardly great. IIRC BMW state the F10 M5 is 10ms & i think the R35 GT-R is 20ms (don't quote me on these).

and that's exactly my point they feel more or less the same. driving is all about feel. if someone tells you it does something better unless you actually can feel the difference where is the improvement?. In comparison the C7 feels quicker than the C6 in terms of gearbox response so there is an improvement I can feel.

so you saying the m5 in the fastest mode is a smooth change it was too violent for me, I felt like it was going to rip the gearbox apart. I never used it.

I'm not sure i said that but if i did say the highest setting was silky smooth then i didn't mean to. I only use that 3rd setting when playing hard or on track as yes it is very quick & you get a good fair thump, however it's certainly not violent (you may have had an issue with yours). As above, if you want to experience violent then you should try the S6 setting in the E60 M5, that did very much feel like the gearbox had been ripped apart.

[W8PMC]

Having owned a regular A6 3.0 TDi with S-tronic before, the one thing I miss from that gearbox is the ability to bypass gears when downshifting. The 8-speed in the RS6 must go through them one by one. It is also not as smooth as say the ZF8 I had in the X5. If you want the gearbox to be really jerky, just put it into sport and try driving like a normal person around town.

I didn't realise that wasn't possible with the the ZF box, but i guess being a regular Auto that must be the case.

With the M-DCT you can bypass any number of gears when wanting to play. Purely pull & hold the downshift paddle & bury the throttle & the car will drop into the lowest gear possible dependant on revs. Can be amusing if not a little scary when dropping from 7th to 2nd.

[Paulm]

I'm not sure i said that but if i did say the highest setting was silky smooth then i didn't mean to. I only use that 3rd setting when playing hard or on track as yes it is very quick & you get a good fair thump, however it's certainly not violent (you may have had an issue with yours). As above, if you want to experience violent then you should try the S6 setting in the E60 M5, that did very much feel like the gearbox had been ripped apart.

There was no issue with mine, reason I know my m8s m5 is the same. I guess being a mechanic, mechanical sympathy is always on my mind. For the sake of 1 or 2 ms slower I never used the fastest setting.

[wildbore]

The 8-speed in the RS6 must go through them one by one.

I don't know where that came from. The ZF is capable of non-sequential shifting; it can traverse virtually the whole gear range in one shift if necessary (8th straight to 2nd).

[DragonRR]

I'm not sure i said that but if i did say the highest setting was silky smooth then i didn't mean to. I only use that 3rd setting when playing hard or on track as yes it is very quick & you get a good fair thump, however it's certainly not violent (you may have had an issue with yours). As above, if you want to experience violent then you should try the S6 setting in the E60 M5, that did very much feel like the gearbox had been ripped apart.

There was no issue with mine, reason I know my m8s m5 is the same. I guess being a mechanic, mechanical sympathy is always on my mind. For the sake of 1 or 2 ms slower I never used the fastest setting.

I used the fastest setting quite a lot and enjoyed it. I agree that it had a bit of a thump to it but if you experienced the older E60 M5 series the SMG system was ridiculous by comparison so using the F10 in its fastest setting felt fine to me!

It is quite hard to get accurate data on shift speeds but there appears to be quite a difference in shift speed between DCT boxes and the ZF auto box in the RS6. Not 1 or 2ms, more like 100-200ms - ZF vs 30-50ms or less with DCT. Running the M5 in full auto however, was, imo, awful compared to the RS6.

[wildbore]

The ZF is 200ms for a change (source=ZF datasheet).

[Paulm]

It is quite hard to get accurate data on shift speeds but there appears to be quite a difference in shift speed between DCT boxes and the ZF auto box in the RS6. Not 1 or 2ms, more like 100-200ms - ZF vs 30-50ms or less with DCT. Running the M5 in full auto however, was, imo, awful compared to the RS6.

I meant switching from setting 1 to 3 on the M5 is only worth 1 or 2 ms so I always used my car in the slowest setting (which was still more than fast enough). I have not looked at how fast they all change as they are all so quick it makes no real difference.

[Heden]

The 8-speed in the RS6 must go through them one by one.

I don't know where that came from. The ZF is capable of non-sequential shifting; it can traverse virtually the whole gear range in one shift if necessary (8th straight to 2nd).

Really? How, I have not managed to do it no matter how hard I tried. I think I need to go out for a run tonight and play around

[Markp]

The 8-speed in the RS6 must go through them one by one.

I don't know where that came from. The ZF is capable of non-sequential shifting; it can traverse virtually the whole gear range in one shift if necessary (8th straight to 2nd).

Agree. Caught me by surprise when I pulled the stick back and hoofed it down a slip road after some services - 6th to 2nd and I was off a bit quicker than intended

[Paulm]

This is very interesting and kind of explains why you cant feel any difference in change speed. Some things can only happen so fast.

Being someone who has coded a standalone aftermarket TCM for the GR6, I do have all the facts and figures on shift times, delays and what the mechanical hardware is capable and where improvements can be made.

Let's be honest, shift performance is only about full throttle up shifting and the acceleration lost during this time. Other shifting conditions effect driveability and feel, and these are important, but when you're talking about faster shift time it's all about performance. First I want to clear up some terminology.

What I regard as 'Shift' time is the amount of time where torque to the wheels is disrupted and the vehicle stops accelerating. Shorting this time makes for better performance while accelerating.
Then there is 'Delay' time, which is the time from when the shift paddle is pulled to when the engine begins to decelerate which is more an annoyance, but can affect performance where your shift doesn't happen when you want it.
There is also engine deceleration time, which is the time when the clutch is slipping, pulling the engine speed into the new gear.

Shift times on a manual syncro box are relatively slow. Typical fast shift might be 300ms, and some might achieve 150ms in a best case scenario.
Then there is a sequential dog box and this can be manually operated or paddle shift, it doesn't matter too much but the engine 'cut' time might be as little as 35ms.
F1 gear boxes are 'zero' shift so no cut on what is effectively a dog box. This is achieved be selecting the next gear before disengaging the previous. When the next gear begins to drive it unloads the previous gear and this is disengaged in the slop the dogs before it explodes. This requires very precise control and very fast and accurate mechanical systems which you would expect from F1!

A dual clutch gearbox (of any make) is also a 'zero' shift gearbox as it engages two gears at once. It doesn't explode because of the slip in the clutches. The 'shift' time is not always zero though, but only because of poor programming for the modifications to the car (engine or trans). The shift feel can be changed dramatically in terms of how hard the incoming clutch is applied and how much torque reduction (by ignition <beep>) is applied to the engine to counter the additional torque delivered to the gearbox from inertial energy coming from engine deceleration.
So 'Shift' time on a GR6 should always be 0ms, no effective interruption of torque from the engine to the wheels.
The time it takes for the engine to decelerate can vary massively from 50ms to 500ms (longer also but the clutches will burn), but torque is always being delivered to the wheels so this is still and 0ms shift time. If the 'correct' amount of torque reduction is applied to compensate for the deceleration rate of the engine then the shift will be smooth, even if deceleration time is really short. The kick in your back is when there is not enough torque reduction, and a lot of people like this. It's potentially better performing also as you're regaining energy lost to accelerate the engine rotating mass in the first place, but often just means the wheels slip instead.

The delay time in the GR6 is from the amount of time it takes from when you pull the paddle until the engine begins to decelerate. Moments before the engine begins to decelerate, the torque driving you forward is transferred through the new gear. The delay (usually ~100ms) is caused by the time for the clutch pressure control proportional valve's magnetic field to rise and move the valve, but more so for the trans fluid to flow and fill the clutch cylinder, taking up the clutch clearance before building pressure and beginning to drive torque. This is a mechanical limitation of the GR6. The OE TCM does have some delays but only a few milliseconds compared to what I could achieve with the Motec TCM when I tested in the best case scenario of full battery power to the control solenoid 1ms after the paddle was pulled. The OE TCM does a pretty good job and the ones I were measuring were LC1 as I did this work years ago.
Different programming, Nismo or Super TCM programs really only effect the shift feel and not shift speed, but can improve actual performance (balancing the torque reduction), or just perceived shift performance.

This data is from a Targa road race car. Mods are limited for the class but it has a Dodson clutch so is a little better shifting time than stock due to not needing maximum clutch pressure to shift.
This was tuned for speed so the torque reduction was minimised on shifting and you can see the resulting shock through the drive train into the wheels as the torque is transferred to the incoming clutch.
Also on reflection it appears the amount of overlap in clutch pressure was just a touch too much as the G Force drops a small amount before the torque is transferred.
Shifting from 3rd to 4th at full throttle. In this case the total time from the moment the paddle is pulled to the kick in the back is ~110ms, and total shift time is ~175ms.

[Bit_evl]

If you want to try a lazy gearbox then go fora recalibration and try a current Merc AMG with the 7DCT. Set the button any way you like and you get lazy, lazy+ and lazy++. Sad as the grunt from the 5.5l BiTurbo was monumental. As was the sound.

I tried a couple of cars when testing prior to selecting the RS6 and think the GTR probably does out change the RS ZF box by a fraction but you cannot terrify four Labradors at a time in a GTR. I agree the faster change modes in dual clutch boxes are possibly faster and certainly can feel faster due to the whack of the engagements.

I don't think there is enough in it that a moment spent reading the road would give better results ?

[DragonRR]

This is very interesting and kind of explains why you cant feel any difference in change speed. Some things can only happen so fast.

Being someone who has coded a standalone aftermarket TCM for the GR6, I do have all the facts and figures on shift times, delays and what the mechanical hardware is capable and where improvements can be made.

Let's be honest, shift performance is only about full throttle up shifting and the acceleration lost during this time. Other shifting conditions effect driveability and feel, and these are important, but when you're talking about faster shift time it's all about performance. First I want to clear up some terminology.

What I regard as 'Shift' time is the amount of time where torque to the wheels is disrupted and the vehicle stops accelerating. Shorting this time makes for better performance while accelerating.
Then there is 'Delay' time, which is the time from when the shift paddle is pulled to when the engine begins to decelerate which is more an annoyance, but can affect performance where your shift doesn't happen when you want it.
There is also engine deceleration time, which is the time when the clutch is slipping, pulling the engine speed into the new gear.

Shift times on a manual syncro box are relatively slow. Typical fast shift might be 300ms, and some might achieve 150ms in a best case scenario.
Then there is a sequential dog box and this can be manually operated or paddle shift, it doesn't matter too much but the engine 'cut' time might be as little as 35ms.
F1 gear boxes are 'zero' shift so no cut on what is effectively a dog box. This is achieved be selecting the next gear before disengaging the previous. When the next gear begins to drive it unloads the previous gear and this is disengaged in the slop the dogs before it explodes. This requires very precise control and very fast and accurate mechanical systems which you would expect from F1!

A dual clutch gearbox (of any make) is also a 'zero' shift gearbox as it engages two gears at once. It doesn't explode because of the slip in the clutches. The 'shift' time is not always zero though, but only because of poor programming for the modifications to the car (engine or trans). The shift feel can be changed dramatically in terms of how hard the incoming clutch is applied and how much torque reduction (by ignition <beep>) is applied to the engine to counter the additional torque delivered to the gearbox from inertial energy coming from engine deceleration.
So 'Shift' time on a GR6 should always be 0ms, no effective interruption of torque from the engine to the wheels.
The time it takes for the engine to decelerate can vary massively from 50ms to 500ms (longer also but the clutches will burn), but torque is always being delivered to the wheels so this is still and 0ms shift time. If the 'correct' amount of torque reduction is applied to compensate for the deceleration rate of the engine then the shift will be smooth, even if deceleration time is really short. The kick in your back is when there is not enough torque reduction, and a lot of people like this. It's potentially better performing also as you're regaining energy lost to accelerate the engine rotating mass in the first place, but often just means the wheels slip instead.

The delay time in the GR6 is from the amount of time it takes from when you pull the paddle until the engine begins to decelerate. Moments before the engine begins to decelerate, the torque driving you forward is transferred through the new gear. The delay (usually ~100ms) is caused by the time for the clutch pressure control proportional valve's magnetic field to rise and move the valve, but more so for the trans fluid to flow and fill the clutch cylinder, taking up the clutch clearance before building pressure and beginning to drive torque. This is a mechanical limitation of the GR6. The OE TCM does have some delays but only a few milliseconds compared to what I could achieve with the Motec TCM when I tested in the best case scenario of full battery power to the control solenoid 1ms after the paddle was pulled. The OE TCM does a pretty good job and the ones I were measuring were LC1 as I did this work years ago.
Different programming, Nismo or Super TCM programs really only effect the shift feel and not shift speed, but can improve actual performance (balancing the torque reduction), or just perceived shift performance.

This data is from a Targa road race car. Mods are limited for the class but it has a Dodson clutch so is a little better shifting time than stock due to not needing maximum clutch pressure to shift.
This was tuned for speed so the torque reduction was minimised on shifting and you can see the resulting shock through the drive train into the wheels as the torque is transferred to the incoming clutch.
Also on reflection it appears the amount of overlap in clutch pressure was just a touch too much as the G Force drops a small amount before the torque is transferred.
Shifting from 3rd to 4th at full throttle. In this case the total time from the moment the paddle is pulled to the kick in the back is ~110ms, and total shift time is ~175ms.

Very informative post, I had some idea about how DCT worked, that it was constant drive and held the current gear whilst selecting the second but didn't know the details.

Let's be honest, shift performance is only about full throttle up shifting and the acceleration lost during this time. Other shifting conditions effect driveability and feel, and these are important, but when you're talking about faster shift time it's all about performance. First I want to clear up some terminology.

I don't totally agree with this statement. From my personal perspective all performance characteristics are equally important. For me the RS6 shifts less predictably (mine was a 13 plate and the software and hardware may have improved since) especially on downshifts. This is important because it affects feel and the ability to overtake which is the time I most experience the cars performance (I tend not to track). I also find that the way one feels a DCT shift down helps you to "know" which gear you are in, in the RS6 I tended to find I'd be looking at the number rather than feeling it.

I had intended to write a short review of my experience with the RS6 after an M5 but never got round to finishing it. I re-read the bit I wrote about performance to check my memory. I had written that I preferred the RS6 in full auto a lot more than the M5 in the same but rarely switched to manual because of the way the ZF box felt. In the M5 I often drove in full manual mode.

I think it's worth pointing out that I really liked the RS6, I would have just liked it more with a DCT box.