01-08-2015, 07:11 AM | #1 |
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LSD with DSC on: will it prevent e-diff from braking
I'm posting my question here even though have an M235i on order. In the 2 and 4 series forums, I started discussion on whether installing the M-P LSD would make sense in street driving (i.e. not on the track), and the discussion has been inconclusive on whether or not the LSD makes any sense with DSC left ON. So
So, here is the question (worded slightly different way) to anyone who actually has the M-P LSD in his car: Assuming DSC is ON (i.e. in public road traffic), when you press on the gas to power-exit a curve or alike - will e-Diff "be faster" and apply brakes to your spinning wheel, rendering LSD useless? Or will LSD take upper hand and prevent e-diff from intervening, thus allowing nice slide with uninterrupted power on the rear wheels? Answering these questions would make it clear whether or not one actually has to turn DSC OFF in order to make any use of LSD...
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01-08-2015, 07:32 AM | #2 |
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First of all, the e-diff is only enabled when the DSC is off. With DSC on, also in DTC mode (or Sport+), there is stability control that will always intervene when the car starts sliding. If you are making inputs with the steering wheel and pedals that the car agrees with, it will not assist you much. If you don't correct the slide, or do it wrong, the car will make a firm intervention with brakes and throttle delete.
A mechanical LSD will allow you to put more power down without getting any wheelspin or powerslide, even with DSC enabled. If you want the car sliding, you should disable the DSC. (I do not have the M-P LSD, but I am a cybernetics engineer with some experience in the topic) |
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01-08-2015, 07:55 AM | #3 |
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Are you 100% sure of that?!! I was positive e-diff is part of DSC and goes off with DSC off...
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01-08-2015, 08:49 AM | #4 | |
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It is more difficult to test that it is disabled when the DSC is on. I have tried, but I can not tell for sure. |
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01-08-2015, 09:25 AM | #5 |
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I have quaife LSD fitted to my JB4 M135i.
In comfort mode ie default when starting up, prior to LSD the TC light would come a lot on public roads here in the UK. 3 reasons 1. they are generally poorly surfaced; 2. it rains a lot here so bumpy surfaces are wet. 3. On stock suspension, rear of the car felt skittish and loose Post LSD, TC light hardly ever comes on [even in the wet] so LSD is reacting before TC intevenes. Even on wet, bumpy roads, rear end of the car feels more planted as traction is improved. Car now grips and goes.
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01-08-2015, 09:34 AM | #6 |
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All this without turning DSC off?
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01-08-2015, 09:54 AM | #7 | |
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DSC Off disables both traction control and stability control, but enables the e-diff. The throttle mapping is always in Comfort mode. |
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01-08-2015, 11:10 AM | #8 |
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Turning off DSC means you are relying less "safety net" systems and more on modulation of your accelerator pedal.
As Ovekam says, with TC systems off, the e-diff comes into play for cars with stock diff to mimick a locking diff for the purpose of improving RWD traction. With an LSD, at least for me using the quaife LSD, e-diff feature is redundant as LSD is more effective at enabling & maintaining traction.
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01-08-2015, 11:30 AM | #9 | |
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01-09-2015, 02:38 AM | #10 |
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I can voucher for Quaife ATB working seamlessly with existing stability/traction control systems on M135i.
This is 2nd RWD beemer I've had with a quaife. 1st car [e91 n54 6mt] didn't have e-diff feature and can confirm it never had problems of sensing slip and engaging. My father lives out in the sticks and there's a big hill near his house. One v icy winter, I was following an Audi SUV up the hill. Audi had to stop to let oncoming traffic down the way. Audi lost its traction despite 4WD and struggled to move, whereas my e91 [c/w winter tyres] re started up the hill w/o issue. Drove round the stricken Audi !!!
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01-09-2015, 02:51 AM | #11 | |
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The BMW Performance LSD is not a TorSen unit, but a clutch pack differential. |
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01-09-2015, 04:20 AM | #12 | |
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Sorry ovekvam - I stand corrected, You are right: eLSD (eDiff) will only come into play when DSC is OFF indeed, so it should be seen not as another electronic "nanny", but a replacement to a "real" LSD in e.g. track drifting where the driver can safely switch off DSC.
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I guess that - after correcting my idea how it actually works with your input - the above is now my question (reworded, but basically the same: will LSD be used efficiently in DSC ON driving scenario)? TIA!
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01-09-2015, 05:32 AM | #13 | |
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The clutch pack units (BMW Performance LSD) and TorSen (Quaife) are activated by torque differences, and will usually react sooner than the car electronics. This way you can drive with a heavier right foot before the DSC warning lamp starts blinking. |
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01-09-2015, 05:48 AM | #14 |
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Thanks! So that the M-P LSD is a "torque-sensitive" type of differential seems to be a crucial part of answering my original question...
Do you think it would be more efficient with DTC active (i.e.limited slip allowed), or in no slip at all conditions?
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just sold: 2013 F10 528i xDrive my AWD beater: 2015 Golf R mk7 DSG my RWD pirate & long-distance cruiser: 2015 M235i AT8, LSD |
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01-09-2015, 05:57 AM | #15 | |
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If you want to drive fast at the limit, the car will eventually hold you back quite a bit by braking too much in both DSC and DTC modes. For sensible driving in public traffic, both DSC and DTC are working well. I think you notice the benefits of the LSD more in DTC than DSC, since you can push closer to the limit in that mode. |
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01-09-2015, 07:25 AM | #16 | |
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01-09-2015, 07:47 AM | #17 |
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Guys - I have 5000 miles since fitting quaife lsd to my car and dry/wet conditions on public road. Don't get hung up about the car e-stability systems, BMW MP drexler or quaife ATB integrate fully.
With an LSD in the rear axle, put simply, the car grips and goes. BP
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01-09-2015, 07:53 AM | #18 | |
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