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07-18-2012, 04:25 PM | #45 |
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It's a shame that so much is different between a 135i and a 1M Coupe, because the easiest way to solve this would just be to compare lap times, skid pad and lane change times of a car with a real LSD and one with the stock fauxLSD. I'd guess that the eLSD times would be closer to an open diff car than one with a mechanical LSD, even a clutch type one, not just a geared one.
Does this really relate to my wife in her DD car? Nope, not at all. |
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07-18-2012, 04:42 PM | #46 | |||
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The bigger issue here is the statement that applying the brakes is pure loss and does not propel the car forward. This is the part that contradicts the statement above. If we assume a 100% efficient open diff with a 1:1 gear ratio, we seem to both agree on this chart: Input = 100rpm | left = 0rpm | right = 100rpm Input = 100rpm | left = 50rpm | right = 50rpm Input = 100rpm | left = 100rpm | right = 0rpm If the input shaft in this scenario does 100rpm and you brake the left wheel down to 95rpm using the brakes on that output shaft, would you not agree that the right wheel will spin at 5rpm? Btw. I'm really enjoying this informative exchange on the efficiencies of mechanical vs. eLSD. Please let me know if anything in the first post needs fixing/correcting as that is the main purpose of this thread. |
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07-18-2012, 04:47 PM | #47 | |
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Please let me know if you want to propose any actual corrections to the information in the first post. I'd be happy to make 'em. |
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07-18-2012, 04:52 PM | #48 | |
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Now, you are correct, a loss is a loss. And again, you are correct in saying that even hardware LSDs are not 100% efficient. I guess another good analogy would be that this system *would* be more efficient if the disc from the brakes on the spinning wheel were attached to the opposite wheel somehow (lets call it magic). In this case, the exchange of energy would be such that even if the brakes were to grab the disc solid, the wheels on both sides would then spin at the same speed. The spinning wheel would pull the other wheel to spin faster by both the action of the diff under braking AND by the action of the disc itself. Not sure if you see what I'm getting at. Man, this is so much more fun than trying to figure out why these stupid digital controls are not receiving my data packets correctly... yeah I'm at work. |
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07-18-2012, 04:52 PM | #49 | ||
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07-18-2012, 04:56 PM | #50 | ||
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So you do agree that RFT's are bad. Now we just need to get you to come around on the eLSD. |
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07-18-2012, 05:04 PM | #51 | |||
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Once the brakes are applied to the spinning side, the diff action will start spinning the stalled side whilst still spinning the side with brakes applied. Quote:
Btw. I edited the first post a little to put less focus on the friction loss differences. |
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07-18-2012, 05:10 PM | #52 | |
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And yes, I have compared my times before/after LSD. And just last week I drove a beautiful 300+hp open diff car and it's hilariously funny. But not in the "safe and fast" way It's absolutely clear to me that everyone who thinks that BMWs eDiff doesn't work has never driven a semi-powerful open diff car before. Do I understand the virtues of a mechanical diff? Sure I do! I spent good money on mine. Do I also understand that BMW's ADB gets you 95% there? Absolutely! |
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07-18-2012, 05:22 PM | #53 | |
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07-18-2012, 05:30 PM | #54 | |
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With all the sensors and mechanisms in place already because of laws. You might as well save money by plopping in a maintenance free open diff and spend a small amount (compared to developing ESC in the first place) of development time to add an eDiff instead. |
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07-18-2012, 05:45 PM | #55 | |
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07-18-2012, 05:55 PM | #56 | |
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Hardware is a fixed cost, you need to find a source for the part, you still obviously need to do R&D, and of course failure testing. The research you mention is a non issue since either solution requires R&D. This means that the difference between the two is the fixed cost, the hardware. One has $0, the other say...$800 per car. Why did BMW remove the rubber mat in the door pockets in 2009? What is that worth? 10c? Why did BMW no longer pre-wire the cars 2009-onwards for all electrical features like they did previously? What is that worth? maybe...$30 in wires Why did BMW remove the power outlet from the tray in front of the shifter in 2009 on most 1-series models? What is that worth? $5? Why did BMW stop installing the little metal hooks in the front of the trunk on some 1-series models? the list goes on... Bottom line, cost is everything, be it 10c or $800. |
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07-18-2012, 06:00 PM | #57 | |
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07-19-2012, 01:29 AM | #58 | |
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Now on corner exits, I did not feel a difference between the two. My car, with linear throttle input, will start spinning the inside tire before getting the ass out. If I am abrupt with the throttle the ass will kick out. If I initiate a slide like that, the car feels pretty solid. When I walk the line of throttle, losing the inside tire and losing the rear end is where the car loses speed. The revs will rise, speed is not gained as quickly and the car is still pointed straight. I felt the same towards the open diff in his car. You guys are WAY more scientific than me, but I feel as if my experience in the cars can still provide to this discussion, hopefully you feel the same. Just don't ask me to explain what I feel mechanically
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07-19-2012, 10:03 AM | #59 | |
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I will say this, it is better than nothing, and will provide better cornering control than a purely open diff. Especially around corners when one throttles up at the exit. I think int2str may be overly optimistic in it's performance, however he is correct in saying that it does make a substantial difference when one pushes the car (slightly) beyond the traction limits. |
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07-19-2012, 10:09 AM | #60 | |
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And BMW wants their cars to be as reasonably priced as possible (for that luxury segment). What use is a 135i that costs way more than the competition due to a feature that maybe 1% know about. And they definitely don't want to take sales away from the 1M and M3. |
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07-19-2012, 12:39 PM | #61 |
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I assumed what my car was doing was due to the eLSD.
Could you help explain to me why my car does what it does? Under hard excelleration in 1st and second, when I'm on it hard enough to spin the tires, like going on an onramp getting on the freeway, my car literally swerves in both directions. If the diff were open completely, one tire would light up I would think, but my car lurches right-left-right-left. I assumed this was the eLSD applying brakes to either of the rear wheels. This is worse in the rain, where the tires spin even easier. My car goes anything but straight under hard excelleration. My car has a tune, DCI, axle back exhaust, Ohlins suspension, M3 bushings, Michelin PSS's, and I know the alignment is good. It has a bit more power than stock, and this issue only happens when I'm accellerationg hard enough to spin the tires. My friend's M3 with LSD goes straight as an arrow. I'm pretty sure that a standard LSD would not make my car do what it does. I know a bit about the subject as I've owned and raced a few cars with LSD's. The only thing I could come up with is the eLSD was causing my car to do what it does. |
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07-19-2012, 12:51 PM | #62 | |
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I'd assume you have traction control fully off? Otherwise that would be your first problem. From there I'd check suspension setup, alignment and the tires... This is what it can look like with the electronic diff: |
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07-19-2012, 01:22 PM | #63 | |
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07-19-2012, 04:52 PM | #64 |
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You can get as technical as you want but the first time I nailed my 135i in first gear I was like, "why the f doesn't this car have a Limit Slip Diff?" The fact that I could tell pretty much sums it up.
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07-19-2012, 04:58 PM | #65 |
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did you not see how much he was working the car to get it to that point?
See how it came out in steps and not one progressive slide? Thats the notchy action of the eLSD that I was talking about. It even tried to bite him back twice |
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07-19-2012, 05:20 PM | #66 | |
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Same driver, more relaxed environment: |
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