12-13-2020, 05:34 PM | #1 |
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Help me interpret some weird track telemetry?
Picked up an F80 “CS” a few weeks ago. Have about 12 sessions / 100 laps around my local circuit - a 2.7M road course. In analyzing my racechrono data, I am seeing something really weird. I have a 10Hz GPS receiver so I trust the racechrono data is accurate.
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Weird data I cannot explain: It seems that I am losing speed every time I make an up shift. Especially from 3 to 4 and then again from 4 to 5 midway through the straight. I shift manually with the paddles and shift at pretty close to redline. Why and I losing speed on the stragiht between shifts???? Does being in MDM somehow limit the engine output between shifts?? Last edited by USSEnterprise; 12-14-2020 at 05:48 AM.. |
12-13-2020, 07:21 PM | #2 |
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First, not sure why you downgraded to GTS MDM, the CS MDM is probably the best there is (most recent iteration).
Second, yes, MDM is quite restrictive and will cut power in anticipation of a potential loss of traction. I am not certain if this is what you are seeing, but it definitely could be the cause. Also, what tires/specs/sizes are you running? If the front-to-rear rolling radius is different to stock, in can exacerbate the MDM interference. Another thing to consider is the Drivelogic mode. I find S3 only works with DSC fully off; MDM will cut back more in S3 than it does in S2.
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12-13-2020, 07:41 PM | #3 | |
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I drive in S2 on the track. I will try leaving it in 4th and nudging the rev limiter next time I’m out to see if I record a higher top speed at the end of the straight. However, its losing speed between 3 and 4 too though. It’s weird that a car will lose speed between shifts on a straightaway. Kind of defeats the whole point of a quick shifting dual clutch tranny. I will eventually turn off MDM once I get to know the car well and its warm out. When running winter track days in a crowded grid its nice to have the safety net of MDM. Would hate to spin out and collide with a GT2RS! Last edited by USSEnterprise; 12-13-2020 at 07:50 PM.. |
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12-13-2020, 07:45 PM | #4 | |
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12-13-2020, 07:54 PM | #5 | |
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I will turn off MDM and set it to S3 and report back next week. P.S: You sure the CS MDM is better? Lots of threads on this topic but none are conclusive. I do find the GTS flash for the diff makes the car rotate much better especially when throttling out of corners. I noticed sharper turn in also with GTS steering map. I don’t perceive any difference in tranny. |
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12-13-2020, 09:09 PM | #6 | |
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As for DSC/MDM, it will cut power or apply brakes in anticipation of loss of traction, not only when there is actual loss of traction. On my car, I can feel it cut power on upshifts when I have zero traction issues with DSC off.
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12-14-2020, 03:08 AM | #7 | |
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Bottom line, IMHO there was some tyre slip happening at full throttle on the straight at speeds of up to 200kmh, and MDM/traction control was pulling power, ever so slightly. Probably giving me 90-95%. So don't underestimate what MDM/traction control can do, especially on not so sticky tyres |
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12-14-2020, 06:10 AM | #8 | ||
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P.S: Once I burn up these tires, I'm getting race tires and a proper alignment with camber plates. Been reading the track alignment thread and making notes. |
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12-14-2020, 07:44 AM | #9 | |
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I am also a firm believer that software and hardware need to be properly matched. The GTS software is optimized around the GTS hardware and CS software is optimized for the CS hardware, mixing and matching often yield sub-optimal results. For instance, the CS DCT software has the GTS higher clutch clamping map since the CS has the same torque rating as the GTS, but the CS has also received the refinements added over time to the base DCT. The reason I mention "placebo" is that EPS does nothing to the steering rack ratio or suspension geometry, all it does is change effort, so I just don't see how it can change turn-in. . Another example, the GTS EPS is adjusted for the front hub carrier unique to the GTS that has a wider front track (different scrub radius will require a different effort map). The power cut you suffer on upshift could well be exacerbated by a mismatched MDM to the engine map for instance. The fact that I am 2.5 seconds faster around my local track with 2019 M4cs than I was with my previous M4 on the same tires tells me that the ///M engineers have done a hell of a good job with the CS tuning. I would rather not tamper with it.
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01-05-2021, 12:09 PM | #10 |
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You're not. There's no way the car slows down with a DCT on a 3-4 or a 4-5 shift on full throttle. There's only three reasons why this would happen:
1. Your car is in limp mode <- highly unlikely/you'd know about it 2. Your bouncing on the rev limiter. 3. You're using GPS to log your speed instead of your ECU. Use an OBDII to get speed not GPS. Consider what's happening to get that value: - You're catching/losing radio waves from multiple satellites that orbit the earth FAST (2x a day) and radio waves can be interrupted by a lot of things around you - The GPS needs to determine what your X-coordinate, Y-coordinate and Z-coordinate is along with time - so waves are required from at least 4 satellites, 10 times per second - You're moving too - relative motion, now your GPS has to interpret the data and mathematically solve those 4 unknowns - The satellite is moving REALLY fast - special relativity has to be considered - more adjustment - Mid-corner a big ass tree pop ups and blocks the wave for an instant, more adjustment is needed - Meanwhile your GPS is under your window and probably cooking from heat, electrons are moving slower Here's how your ECU reads speed: - Tire spin - Magnet says hi to another magnet every revolution - Revs/Second gets converted to MPH/KPH with a preset tire diameter So yeah.... GPS systems are INCREDIBLE and INSANELY accurate but they're also extremely complex and error is present (typically insignificant but more present with instantaneous events like change in acceleration). Lateral G is much more accurate when your GPS position data is calculated using ECU speed. The only drawback to ECU speed is if you're using a different tire diameter but even then, shouldn't impact it that much. My 305/35R18 NT01 read 1 mph faster than actual at 90 mph (0.3 mph faster than actual at 30 mph). |
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01-06-2021, 10:13 PM | #11 |
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Never seen that before. I have a manual and im sure my 4-5 shift is slower than your DCT in any mode. Somethings not right with the gps. You have a yellow then orange then green when its suppose to be acceleration.
When you check the mph speed around the lap, what does it show? That should clear things up. Where was the gps receiver mounted? Does it have a clear line of sight to the sky? Do you have metallic tint where it was mounted? |
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01-10-2021, 12:02 PM | #12 | |
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My 10hz external receiver is mounted with a clear view of the sky and shows more than adequate satellite locks. The GPS data is accurate and I'm afraid I am indeed losing speed between shifts. I verified this with my Garmin Catalyst's data as well. I also tried shifting earlier, thinking perhaps I was past the 7200 rpm power peak and causing this issue. Same story. There is a definite lag and slowness between upshifts when WOT even when shifting earlier in the rev band. This leads me to agree with CanAutM3 that the cause of the issue has to be MDM mode. It's cold down here in TX with track temps in the high 40s and low 50s so I am leaving MDM on. One of these days when we have a 70+ degree day and tarmac temps are good, I'll turn off DSC altogether and see if this issue goes away. I'll report back. |
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01-10-2021, 04:55 PM | #13 | |
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I don't think the inputs at the moment you shift from 3-4 or 4-5 will set off MDM in a straight line unless your tires are cooked. It'll mostly ruin your corner speeds and corner exit. |
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01-13-2021, 06:48 PM | #14 | |
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For optimal acceleration, you want to maximize power. Shifting 3rd at ~7,000rpm lands 4th at ~5,250rpm which yields about the same power level. Shifting 4th at ~6,800rpm lands 5th at ~5,325rpm. 1st and 2nd need to be redlined. That's what I use. My data logs clearly showed MDM cutting power on 3-4 upshifts when there was zero issue with DSC off. Like I said, DSC will cut power in anticipation of a loss of traction, it does not need to see an actual increase in slip to do so.
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01-13-2021, 06:57 PM | #15 | |
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