11-11-2017, 04:17 PM | #45 |
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The whole concept doesn't make sense. Rev matching is more useful on downshifts of more than one gear, where the RPM change would be greater. This thread is in in the B58 board. To me, that means that the change wasn't done on the 4-cylinder engines, making the whole thing sound more like some engineer's screw-up. I could imagine someone deciding that NOT doing rev matching on single-gear down shifts was OK, thinking that the adjustment would be more minor, and then doing it backwards. I am taking my '17 440ix in for its first service Monday, and I will ask ahead of time whether they think it needs some sort of software update. I would prefer that things work "the old way".
Last edited by rak299; 11-11-2017 at 04:23 PM.. |
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11-11-2017, 09:52 PM | #46 | |
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As for whether it applies to the B48? No clue.. how many B48s are sold with manuals? And does the 330 manual have downshift rev matching? |
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11-12-2017, 09:18 AM | #47 | |
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I'm curious why people are getting updated software flashes to begin with? Is something being fixed or are the dealers just doing it as protocol? |
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11-12-2017, 10:36 AM | #48 |
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I am going in tomorrow for a normal, 12-month service (only 7k miles). I will try to ask the protocol and see whether they have some normal procedure to flash or some service advisory. I'll post back after.
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11-12-2017, 12:57 PM | #49 | |
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As I noted in my post, that was the explanation I was given. In my case, it was specifically to address a drivetrain malfunction message. They scanned the car, escalated to corporate, corporate said to do a software update to address the issue. The drivetrain malfunction message has not recurred since, but it only showed up once for me anyway (annoyingly enough, it showed up after they pulled up my car to give it back to me, but before I got in it, after an oil change). |
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11-12-2017, 01:16 PM | #50 |
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11-12-2017, 03:00 PM | #51 | |
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11-13-2017, 12:41 PM | #52 |
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Is there a way to outright disable this? I'm perfectly fine blipping my own throttle and do not need a computer in the way. The computer and I are walking on each other...
I'm really confused why so many people WANT this 'feature' |
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11-13-2017, 02:59 PM | #53 | |
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To be honest i didn't like the idea but it doesn't bother me that much anymore. Especially when I tried to heel-toe and realized how crappy the positioning of the pedals is. It took a while to get used to because holding the brake while shifting shifted my focus a ton, so mentally I had to be at ease with it. But now it's a force of habit. Plus, per the point of this thread, i still have plenty of opportunity to rev match myself when i skip gears. If they had a button or coding to turn it off, i probably would. But imo it's not as big of a headache as people make it out to be. |
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11-13-2017, 03:13 PM | #54 |
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I've read that, but it still happens on my 340 in all modes, even sport+ .... or any mode and messing with the TC button. I've read conflicting reports that coding the 'clutch pedal on start' / 'brake pedal on start' kills it. Some say it does, some say no difference.
As far as I understood it, it triggers when the shifter starts to pass into the gate for the target gear. So idk how going from 6-5 would be any different than 6-4, as both just pass through N to each gear. I do wonder how this works...... In my day the only electronics near an MT were A) the ground wire, B) the starter, C) the speed sensor, and D) the reverse lights... that's it! Anyway .. not to thread jack, hope you get it 'fixed' whatever that entails. |
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11-13-2017, 04:02 PM | #55 | |
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If you turn traction control off (by holding down the DSC button) rev matching will be disabled.
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Last edited by jpsimon; 11-13-2017 at 04:56 PM.. |
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11-13-2017, 07:22 PM | #56 | |
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I will try to find out a little more on how this works .. i'm wondering if you change the tire size if it's smart enough to adjust or if that can be programmed... i.e. your tires are 10mil taller over OE, does the computer always overblip. I haven't 'used' it enough but was also wondering if it continuously adjusts the revs if the car's speed changes if you jokingly take an inordinate amount of time between gears.. And I can't imagine why the programmer would now look at the source gear either.. |
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11-13-2017, 08:17 PM | #57 | |||||
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The current configuration where it only automatically rev matches on single gear downshifts... really pisses me off, because as I've been re-developing the muscle memory to rev match myself, now I screw with it when it's trying to rev match as well, and it fucks up my timing, because most of my down shifts are more than one gear, but sometimes I only downshift one gear and it steps in as well. Quote:
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Vehicle speed sensor's raw output is actually transmission output shaft RPM, which then gets multiplied by final drive and (divided by?) diameter of the tires to determine the speed in mph, so the first division isn't necessary. Final drive never changes, so instead of dividing that by the gear ratio in real time, you can just program in what ( final drive / 1st gear ratio ) is, (final drive / second gear ratio ), etc, etc. are, so it's a very simple math problem, updated multiple times a second, so if your speed changes, the target rpm changes in direct relation to speed. Quote:
Doing it for only some downshifts requires tracking state a lot more. What gear were we in previously? etc, etc. Last edited by Araemo; 11-13-2017 at 08:27 PM.. |
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11-13-2017, 08:38 PM | #58 |
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My point was if you change the tire size the speedo will always be off... so it for sure matters for the blip calculation. It will misblip every time if you change nothing aside from the OD of the tires from stock.
Likewise obviously if you change your FD gear out it will radically misblip and your speedo reading is far different from actual speed. I bet they have a hard coded number in there for the FD and the stock tire OD as well. Put 22s on yo and see how the blip works. |
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11-13-2017, 09:35 PM | #59 |
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When I had my car in for service today, I asked the "service adviser" and he didn't know what rev matching was or why you might want it or not want it. He said I had no software updates suggested for my car, but said he would talk to the foreman to see what he knew. They were going to call back, but I heard nothing.
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11-13-2017, 10:05 PM | #60 |
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it doesn't matter what your actual speed is. when rev matching, the car is comparing the hub speed (wheel sensor) to the engine speed. and the hubs diameter will not change regardless of your wheel size. what will change is the speed on the dash vs your actual moving speed, which is irrelevant to rev matching.
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11-14-2017, 01:08 AM | #61 |
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I generally double down and on my gears and the rev matching never shows up. I think if you blip the throttle between gears it doesn't match. I will confirm tomorrow
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11-14-2017, 09:17 AM | #62 | |
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11-14-2017, 12:23 PM | #63 | |
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It does still, but if you blip to above the target rpm before pushing the gear lever into gear, it has nothing to do, but if you watch it, RPMs should drop to the 'correct' rpm, then stop dropping for a moment (1-2 seconds, I think?) before it gives up on rev matching and lets them drop again. |
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11-14-2017, 01:57 PM | #64 |
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Ok, I didn't know about this ABS hub sensor ... I didn't realize is it's reading the hub rpm in gear A vs the hub to gear B, which is a relative calculation only between gear A vs B. I didn't know about that sensor and figured it would be MPH (VSS/FD/tire) based. Interesting... I guess this is a 17 BMW vs my 96 honda I was about to put the 4.9 FD in.
So, I can freely move to slightly different tire diameters (not that I will) and my speedo will still read correctly (as this is also hub based), and I won't worry about the computer misblipping. (Though I will always do that manually and still seek to disable it outright, preferably keeping DSC on). My whole point was it would really suck if a simple tire change caused it to always underblip. |
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11-14-2017, 02:53 PM | #65 | |
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11-14-2017, 11:16 PM | #66 | |
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Vehicle speed sensors in BMWs (and every other car I've owned) read the RPM of the transmission output shaft, and the control unit that converts that to MPH has a ratio it applies that's based on the final drive ratio and tire diameter. Which is why changing either will make your speedometer inaccurate. However, since the spot the 'vehicle speed' is measured is before either final drive or tire diameter are involved, changing either of those will not impact the automatic rev matching. Lets break it down further... In third gear, at 45 MPH, the engine is at 3000 RPM. So if you're driving in 5th at 45, and want to downshift to 3rd, you blip to around 3000 RPM to rev match. If you then increase your tire size by 11% (255/40R18 to 255/50R19.. ridiculous, but just pretend you did it). When your speedometer says 45 MPH, you'll actually be going 50 MPH. But, if your speedometer says 45 MPH, and you are in 3rd gear, you'll still be at 3000 RPM, even though you're actually going 50 MPH. So, even though you're going 50 MPH, if you're in 5th and want to downshift to third, you'll still be blipping to around 3000 rpm to match the 3000 rpm at an indicated 45 MPH. And this is basically exactly what the computer will do, so it won't be bothered by tire diameter changes. So, even if the engine control unit based the rev matching on vehicle speed in MPH, it would still work accurately if you changed final drive or overall tire diameter, because those multipliers apply after where it measures vehicle speed, which is why your speedometer is inaccurate after changing either of those. None of this has anything to do with the wheel speed sensors on the wheel hubs, which are used for ABS, ESC, etc. |
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