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      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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Quote:
Originally Posted by ovekvam View Post
First of all, the e-diff is only enabled when the DSC is off.
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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Quote:
Originally Posted by moldcad View Post
Are you 100% sure of that?!! I was positive e-diff is part of DSC and goes off with DSC off...
I have checked quite a lot of internet sources, and almost all of them (including the manual that comes with the car) confirmes it. I am 100 percent sure that the e-diff is enabled in DSC Off mode, as it is quite easy to feel when it is working.

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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Quote:
Originally Posted by moldcad View Post
Well, no offense please - but aren't you confusing DSC OFF with DTC ON?
DTC is a special DSC mode where the stability control is still active, but traction control is pretty much disabled. Sport+ is the same as DTC, but with sport mapping of the throttle.

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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Quote:
Originally Posted by moldcad View Post
All this without turning DSC off?
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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Quote:
Originally Posted by Bee Pee View Post
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.
A TorSen-unit as the Quaife ATB, can sometimes struggle to lock up properly when the friction is extra low on one side, like when one wheel is airborne. With some help from the e-diff, that is all it takes to get it going. I think they will work very well together.
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      01-09-2015, 02:38 AM   #10
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Quote:
Originally Posted by ovekvam View Post
I think they will work very well together.
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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Quote:
Originally Posted by Bee Pee View Post
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 !!!
I have seen it happen on Quaife units. It is only when one tyre has almost no traction. On the E91, it was possible to use the traction control to give the Quaife the necessary preload to start locking up.

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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Quote:
Originally Posted by ovekvam View Post
First of all, the e-diff is only enabled when the DSC is off.
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.

Quote:
Originally Posted by ovekvam View Post
A mechanical LSD will allow you to put more power down without getting any wheelspin or powerslide, even with DSC enabled.
However, am still not quite comfortable with the above statement - doesn't LSD actually *need* some wheelspin (actually, a difference in left/right wheel spins) to activate? And if so - assuming I'm still protecting my stability with DSC on - will the amount of wheel spin that DTC allows suffice for LSD working efficiently *before* DSC kicks in, cutting power and applying brakes to any of the 4 wheels (not just the rear) it feels necessary to prevent stability loss?

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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Quote:
Originally Posted by moldcad View Post
However, am still not quite comfortable with the above statement - doesn't LSD actually *need* some wheelspin (actually, a difference in left/right wheel spins) to activate? And if so - assuming I'm still protecting my stability with DSC on - will the amount of wheel spin that DTC allows suffice for LSD working efficiently *before* DSC kicks in, cutting power and applying brakes to any of the 4 wheels (not just the rear) it feels necessary to prevent stability loss?

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!
There are different types of LSDs. The viscous units (like the ones used in the BMW E30 325iX) are activated by wheelspin. The more difference in wheel speed, the more it locks up. The fake e-diff is also in this category. You can feel it lagging a bit when driving on the limit.

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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      01-09-2015, 05:57 AM   #15
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Quote:
Originally Posted by moldcad View Post
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?
It depends on the driving conditions. If you are driving on solid ground, like tarmac or ice, no slip (DSC) is usually the most efficient way to get the power down. On loose surfaces like snow or gravel, the tyres will get more grip by digging into the road by some wheelspin (DTC).

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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Quote:
Originally Posted by ovekvam View Post
I have seen it happen on Quaife units. It is only when one tyre has almost no traction. On the E91, it was possible to use the traction control to give the Quaife the necessary preload to start locking up.

The BMW Performance LSD is not a TorSen unit, but a clutch pack differential.
In wintry conditions, TC is off so as not to cut the power in the event of one or both rear wheel slipping.
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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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Quote:
Originally Posted by Bee Pee View Post
With an LSD in the rear axle, put simply, the car grips and goes.
You also have the added benefit of more predictable and sharp handling if you choose to go drifting with DSC Off. The e-diff works, but not as well as a real, mechanical LSD.

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      01-09-2015, 08:12 AM   #19
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Great photo !!
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