Downshifting question DCT

[SPQR M3]

Is it possible to downshift directly from, say, 5th gear to say, 3rd or 2nd in one move?

Also, do most of you guys downshift as you approach a stop or do you just let the DCT do it for you (while in S mode).

[Kitsune]

As part of an automated design (Anti-Stall I believe was the term, but not positive), the DCT can downshift more than one gear, but not manually so far as I know.

[vamosvanos]

From my experience yes one can downshift more than one gear.

[SPQR M3]

Originally Posted by vamosvanos

From my experience yes one can downshift more than one gear.

Thanks, care to elaborate on how it's done?

[SenorFunkyPants]

You can fast multi click on the downshift paddle if you want to swop from say 5th to 2nd, but I'm not convinced that the command is always handled well by the system (possibly as a result of the way the DCT tries to have the next predicted gear ratio preselected). My preference is always to single downshift, you can string a series of downshifts together very quickly without issue even under heavy braking.
You can let software do the the anti-stall downshifts as you approach a junction but you risk the DCT being in the process of making a downshift when you want to reapply the power which can leave you with no drive for a short time (dependant on which software version your car has). If you make the downshifts yourself, the downshift is quick and certain, the higher the gearshift mode (s1->s6) the more rev matching you get = faster downshifts, whereas in S1 you can heel and toe during the (what would otherwise be a slow) downshift to produce a fast downshift (my favourite and default daily driving gearbox mode).

[Kitsune]

Originally Posted by SenorFunkyPants

You can fast multi click on the downshift paddle if you want to swop from say 5th to 2nd, but I'm not convinced that the command is always handled well by the system (possibly as a result of the way the DCT tries to have have the next predicted gear ratio preselected). My preference is always to single downshift, you can string a series of downshifts together very quickly without issue even under heavy braking

This is about the only way I see to do it. My response was based off the understanding that they wanted to downshift more than one gear 'at once', something the DCT can only do on its own. Quickly hitting the paddles though should do the trick as long as it registers.

[SenorFunkyPants]

I don't know whether the hardware can physically skips gears or if it has to go through every downshiftshift squentially.
I do sometimes make multi-downshifts but I don't like the time it takes to execute them which doesn't always seem constant or predictable.

[vamosvanos]

Originally Posted by SenorFunkyPants

You can fast multi click on the downshift paddle if you want to swop from say 5th to 2nd, but I'm not convinced that the command is always handled well by the system (possibly as a result of the way the DCT tries to have the next predicted gear ratio preselected). My preference is always to single downshift, you can string a series of downshifts together very quickly without issue even under heavy braking.
You can let software do the the anti-stall downshifts as you approach a junction but you risk the DCT being in the process of making a downshift when you want to reapply the power which can leave you with no drive for a short time (dependant on which software version your car has). If you make the downshifts yourself, the downshift is quick and certain, the higher the gearshift mode (s1->s6) the more rev matching you get = faster downshifts, whereas in S1 you can heel and toe during the (what would otherwise be a slow) downshift to produce a fast downshift (my favourite and default daily driving gearbox mode).

+1

[mkoesel]

Originally Posted by SPQR M3

Is it possible to downshift directly from, say, 5th gear to say, 3rd or 2nd in one move?

Yes, but perhaps not exactly like you think. You can achieve a multi-gear downshift by pushing the gas pedal past the detent. In auto mode, the transmission will drop down to the best gear for accelerating automatically. In manual mode the transmission will drop to the best gear for accelerating only if you pull the "-" paddle (or use the stick). So you aren't picking the exact gear yourself. But the transmission will go from 5th directly to 2nd (for example) if you are cruising along at 45mph in 5th gear and do this procedure.

Granted, this does not provide a way to do a multi-gear downshift on deccleration. I just use multiple paddle pulls for that.

Also, do most of you guys downshift as you approach a stop or do you just let the DCT do it for you (while in S mode).

I always downshift myself. Its more fun, more "correct" (arguably - though on the street vs. on a track the need is not as great, true), and it can help avoid the lag.

Originally Posted by SenorFunkyPants

...whereas in S1 you can heel and toe during the (what would otherwise be a slow) downshift to produce a fast downshift (my favourite and default daily driving gearbox mode).

You talk about this often, SFP, and it intrigues me. I never drive in S1. To me, heal-toe is a process that requires the ability for the engine to free rev momentarily, either while the transmission is in neutral (double clutch) or the clutch is simply disengaged (single clutch). Its not clear to me how or why the transmission can allow this in the context of the heal-toe process. But, as I say, it does intrigue me. Can you explain how this all works from a DCT-operation perspective?

[SenorFunkyPants]

Originally Posted by mkoesel

You talk about this often, SFP, and it intrigues me. I never drive in S1. To me, heal-toe is a process that requires the ability for the engine to free rev momentarily, either while the transmission is in neutral (double clutch) or the clutch is simply disengaged (single clutch). Its not clear to me how or why the transmission can allow this in the context of the heal-toe process. But, as I say, it does intrigue me. Can you explain how this all works from a DCT-operation perspective?

In S1 the downshift is slow enough that the DCT software releases control of the throttle for a short time and in that moment you can blip the throttle for a rev matched downshift.
Its more toe and toe than heel and toe in the sense that I cover the brake and throttle with the wide part of my shoe and just rock my foot to the side to push the throttle. Even a tickle is enough to transform the otherwise slow S1 downshift into 2nd or 1st into a quick smooth downshift and a confidence that you are in the gear you want.

I've just come back from a quick drive where I found you can indeed make quick multigear downshifts...the higher the gearshift mode the better it works..in S6 I managed 7th to 2nd in one shift but if you try it yourselves you do need be at low revs in 7th as it will rev match the shift up to rev limit if it can.
The only thing I noticed was that when I didn't click the paddle quick enough it went from 7th to 3rd and then 2nd but it was still pretty quick.

[gr8000]

Originally Posted by SenorFunkyPants

The only thing I noticed was that when I didn't click the paddle quick enough it went from 7th to 3rd and then 2nd but it was still pretty quick.

Why do you need to click the " - " paddle repeaditly many times in order to downshift multiple gears instead of pushing the gas beyond the kickdown pont and click the " - " paddle once? The system will downshift as many gears as needed (and have the engine rev matched) instantly to get you to the optimal gear for max acceleration at any given speed, eg from 7 to 2nd if needed. Why do you need to click the " - " paddle 5 times to achieve the same result?

[mkoesel]

Originally Posted by SenorFunkyPants

In S1 the downshift is slow enough that the DCT software releases control of the throttle for a short time and in that moment you can blip the throttle for a rev matched downshift.
Its more toe and toe than heel and toe in the sense that I cover the brake and throttle with the wide part of my shoe and just rock my foot to the side to push the throttle. Even a tickle is enough to transform the otherwise slow S1 downshift into 2nd or 1st into a quick smooth downshift and a confidence that you are in the gear you want.

Thanks for the explanation. I'll have to try this out. It still seems like there could be risk of unintended sudden acceleration if the clutch happens to be engaged when you think it isn't. No? I guess I should just try it and see.

I've just come back from a quick drive where I found you can indeed make quick multigear downshifts...the higher the gearshift mode the better it works..in S6 I managed 7th to 2nd in one shift but if you try it yourselves you do need be at low revs in 7th as it will rev match the shift up to rev limit if it can. The only thing I noticed was that when I didn't click the paddle quick enough it went from 7th to 3rd and then 2nd but it was still pretty quick.

You're talking very rapid paddle clicks in succession, right? Yeah, this I do all the time.

But it was never clear to me whether the transmission was genuinely skipping gears in the process. That is, are the shift collars moving around inside the transmission in preparation to shift into each of the gears you pass through? Or is there enough of a delay built into the system such that it holds off even starting to execute the gear change until no more downshifts are detected? I guess it doesn't really matter as long as you get the effect of a multi-gear downshit. But I do sometimes wonder about wear, if the former is really what is going on inside. Because of that, I do still sometimes wish there were a way to do a true single-pull multi-gear downshift on deccelertaion like you can when accelerating. Not sure what kind of interface you'd use to tell it that's what you wanted it to do though.

[mkoesel]

Originally Posted by gr8000

Why do you need to click the " - " paddle repeaditly many times in order to downshift multiple gears instead of pushing the gas beyond the kickdown pont and click the " - " paddle once?

Because - at least as I understood him - he is talking about downshifting while deccelerating, not while accelerating.

One thing I forgot to add to my last post though, is that, I suppose you could trick it by gunning the gas past the detent, waiting for the multi-gear downshift, and letting off the gas immediately and hitting the brake. But this seems dangerous, convoluted, and just not really a good idea overall.

[SenorFunkyPants]

Originally Posted by mkoesel

Thanks for the explanation. I'll have to try this out. It still seems like there could be risk of unintended sudden acceleration if the clutch happens to be engaged when you think it isn't. No? I guess I should just try it and see.

I think once you have the timing right it works very well, I find some satisfaction in having a little bit more control of the downshift process.

Originally Posted by mkoesel

You're talking very rapid paddle clicks in succession, right? Yeah, this I do all the time.

But it was never clear to me whether the transmission was genuinely skipping gears in the process. That is, are the shift collars moving around inside the transmission in preparation to shift into each of the gears you pass through? Or is there enough of a delay built into the system such that it holds off even starting to execute the gear change until no more downshifts are detected? I guess it doesn't really matter as long as you get the effect of a multi-gear downshit. But I do sometimes wonder about wear, if the former is really what is going on inside. Because of that, I do still sometimes wish there were a way to do a true single-pull multi-gear downshift on deccelertaion like you can when accelerating. Not sure what kind of interface you'd use to tell it that's what you wanted it to do though.

I only did the 7-2 downshift a couple of times and its quite impressive in S6 as it rev matched up to 5000 rpm, the actual shift seemed too fast to have gone through each gear but I could be wrong. As you suggest maybe the gearbox does hold off making the shift if it detects a multi click of the paddle.

[gr8000]

Originally Posted by mkoesel

Because - at least as I understood him - he is talking about downshifting while deccelerating, not while accelerating.

Sorry, my bad - my read was too quick.

Originally Posted by mkoesel

One thing I forgot to add to my last post though, is that, I suppose you could trick it by gunning the gas past the detent, waiting for the multi-gear downshift, and letting off the gas immediately and hitting the brake. But this seems dangerous, convoluted, and just not really a good idea overall.

I thought of it too Too dangerous indeed!

[mkoesel]

Originally Posted by SenorFunkyPants

I only did the 7-2 downshift a couple of times and its quite impressive in S6 as it rev matched up to 5000 rpm,

Oh it will go much higher than 5k RPM, trust me. I regularly get it up to the 8k range in 2nd gear, when exiting an expressway for example. It will even go up to around 7k in 1st gear. Tons-o-fun.

Actually that just made me wonder about something I've never tried before. I wonder what happens if you use the multi-stage downshift accerleration function (the one discussed above, using the throttle detent) at a very low speed. Will it actually drop you into first gear or will it only go to second? I have never even thought to try this on a street where I'd be moving slow enough for first gear to be available so I don't know. I'll have to try it out later.

the actual shift seemed too fast to have gone through each gear but I could be wrong. As you suggest maybe the gearbox does hold off making the shift if it detects a multi click of the paddle.

Yeah, I know it can't actually be doing the entire shift process with each click. But in theory it could - with the clutch disengaged the whole time - still be running through the process of moving the collars in and out for each gear, so all that it would have to do is let out the appropriate clutch to complete the shift. In other words, it would be the same as dropping the shift lever into each gate when doing multi downshifts with a traditional manual transmission, all while keeping the clutch pedal in. You'd never do this with a manual of course (unless you are a very indecisive person ), but you see what I mean, right?

[!Xoible]

... awaits Swamp's response

[SenorFunkyPants]

Originally Posted by !Xoible

... awaits Swamp's response

Is he going to be long cos I've got things to do!!

[swamp2]

What most are saying is correct. I'll add/summarize:

1. While in auto mode a large and fast throttle depression will grab multiple gears automatically, skipping the in between gears. S5 does this with less throttle input than S2 and similarly across the Drivelogic modes.
2. While in auto modes a full depression of the pedal will indeed give you a "maximum" downshift to the gear that provides the best acceleration. Again the intermediate gears are always skipped. I'm fairly sure you can't get a 7->3 downshift or 7->2 in S1 mode. It will only shift a couple gears down. All the other modes will provide a maximum downshift.

The shifts for either of these scnarios are fast but not nearly as fast as a single gear auto or manual downshift.

3. While in manual mode you have to click the paddles very very quickly to actually skip an intermediate gear. I know you can skip one gear but not sure if you can skip 2, say 7->4.
4. While in manual mode if the go quickly to WOT and hold the downshift paddle you activate the kick down mode which just like #2 above will give you a fast and maximum downshift remaining in manual mode the whole time. This is really fun.

Just as a note whether in auto or manual modes upshifts NEVER skip gears. The ability to skip gears is one characteristic that makes the DCT absolutely not a sequential.

[SenorFunkyPants]

Originally Posted by mkoesel

In other words, it would be the same as dropping the shift lever into each gate when doing multi downshifts with a traditional manual transmission, all while keeping the clutch pedal in. You'd never do this with a manual of course (unless you are a very indecisive person ), but you see what I mean, right?

Yes I do...I tried the 7th to 2nd shift in S1 last night and thats a totally different shift..the indicator goes straight from 7 to 2 but the actually shift takes about 2 secs with a half hearted rev match at the end compared to less than 0.5 secs for the same shift in S6.

[zenderm3]

So SenorFunky - are you saying that you went straight from 7th to 2nd?

[SenorFunkyPants]

Originally Posted by zenderm3

So SenorFunky - are you saying that you went straight from 7th to 2nd?

The gearbox gives every impression that it makes the shift from 7th -> 2nd in one shift in S6...but it is hard to be certain what exactly is going on inside the DCT without definitive information from Getrag/BMW.
Its interesting from a technical point of view but not something that you are going to do in day to day driving.