[moldcad]

Thanks, and no bad feelings

[foamie]

Originally Posted by moldcad

I *assume* the same, but with the LSD price I need to be 100% positive - have already sent inquiry to BMW Poland.

PLEASE let us know what the response is.

[moldcad]

If only I get some positive info I'll share it here, no worries. But frankly, with so little experience with things like LSD here, BMW may be unable to help without escalating the thing higher (to the AG)....

[moldcad]

Originally Posted by Killramos

I don't think that's true. DSC OFF really has no nannies.

Actually I learn the answer I got on another forum (that eDiff is *only* active with DSC OFF) turns to be true! This means 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.

But assuming LSD actually *needs* some wheelspin (or difference in left/right wheel spins) to kick in, my question is still valid:

- will LSD be used efficiently in DSC ON driving scenario?
- won't DSC stability control action (engine power taming/one or more of all 4 wheels braking) prevent LSD from being efficiently used?

I hope that the amount of wheelspin as allowed by DTC (before full DSC kicks in) will be sufficient for LSD to work, but this is now my main question...

[moldcad]

Originally Posted by pikcachu

When the dynamic stability control function DSC is deactivated, the torque-sensitive mechanical limited-slip differential in the rear axle ensures traction-optimised distribution of drive torque between the rear wheels. It reduces the slip that occurs on the wheel with less grip by transferring more drive power to the other wheels using a blocking effect. This converts engine power into forward momentum as effectively as possible so as to be able to accelerate out of a bend even more dynamically, for instance."

Well, I'm slowly gathering bits and pieces together and can tell you what I know so far:

1. eDiff (eLSD) only works with DSC off, so it's a fake LSD for those drifting on a track, where turning DSC off is appropriate

2. When on public road, we usually don't want to switch DSC off, so we're left without any LSD - until we add the M-P LSD. Why did I stress M-Performance (i.e. the one we're discussing here)? Well, because unlike e.g. viscous units, the clutch pack units (BMW Performance LSD) and TorSen (Quaife) are activated by torque differences (this is why I bolded this fragment out in your quote), and not wheelspin difference; also they will usually react sooner than the car electronics

So, DSC ON should not - within reasonable limits - prevent the M-P LSD from efficiently putting more torque to the pavement!

This conclusion - although still unconfirmed in 100% by BMW, which was to be expected - effectively ends my little "research" - I'd like to thank all of you for your input (including those in similar threads of mine on the other fora). I for one am definitely adding M-P LSD to my M235i !

[tke743]

FYI for the OP. The roads are CRAPPY here today and I don't have the LSD yet (I get it on the 20th). No problems at all. the e-diff/DSC works great in the snow, slush, ice, and random slippery crap on the roads today. LSD is not needed for slippery weather, it is only needed for top performance.

[quenotte]

To my mind, a mechanical LSD will react way sooner than DSC...

[pikcachu]

Originally Posted by moldcad

Well, I'm slowly gathering bits and pieces together and can tell you what I know so far:

1. eDiff (eLSD) only works with DSC off, so it's a fake LSD for those drifting on a track, where turning DSC off is appropriate

2. When on public road, we usually don't want to switch DSC off, so we're left without any LSD - until we add the M-P LSD. Why did I stress M-Performance (i.e. the one we're discussing here)? Well, because unlike e.g. viscous units, the clutch pack units (BMW Performance LSD) and TorSen (Quaife) are activated by torque differences (this is why I bolded this fragment out in your quote), and not wheelspin difference; also they will usually react sooner than the car electronics

So, DSC ON should not - within reasonable limits - prevent the M-P LSD from efficiently putting more torque to the pavement!

This conclusion - although still unconfirmed in 100% by BMW, which was to be expected - effectively ends my little "research" - I'd like to thank all of you for your input (including those in similar threads of mine on the other fora). I for one am definitely adding M-P LSD to my M235i !

I understand what you say but not sure why they added "When the dynamic stability control function DSC is deactivated" to the beginning...

what i don't quite get is that if both wheels are not slipping then the torque sent to each of them should be the same no?

hence the answer from one of the admins that went to the pref even in LV

"A mechanical LSD is always 'on'. It is a mechanical locking device.

However, with DSC engaged, your inside wheel slip will be curbed much sooner by the DSC braking the individual inside wheel, well before it has had enough slip to engage the LSD.

The LSD is always on, but can't be felt until you turn off DSC. Otherwise, DSC will interrupt your power well before the LSD even has a chance to take hold."

[pikcachu]

2 interesting threads

http://www.bimmerfest.com/forums/sho...88&postcount=5
http://forum.miata.net/vb/showthread.php?t=233722

"Yes, in theory you can have the LSD working with the DSC/TSC on. As said before the LSD is a mechanical device that maximizes the available grip you can put power to.
i.e. if your turning into a corner and apply power, your inside wheel will not have much grip since it's unloaded to put power. If you have an open differential, that inside tire will break loose spin and all the power diverted to the inside wheel that doesn't have grip, while the outside tire which has available grip doesn't get the power. LSD enables the torque to be applied more to the outside wheel rather than the inside wheel, hence giving you more accelleration out of the corner.

In the same scenario if you apply so much power with the LSD such that your outside tire starts to slip and your powersliding, your DSC and TSC will kick in decreasing your throttle and applying brakes to certain corners such that you don't spin out of control and maintain the direction your intended on going."

[moldcad]

Originally Posted by tke743

FYI for the OP. The roads are CRAPPY here today and I don't have the LSD yet (I get it on the 20th). No problems at all. the e-diff/DSC works great in the snow, slush, ice, and random slippery crap on the roads today. LSD is not needed for slippery weather, it is only needed for top performance.

Are you driving with DSC OFF on such crappy roads as you describe? Because if you are so sure your eDiff works so great in the snow, slush, ice etc., you must be - with DSC on, eDiff doesn't work at all!

[foamie]

IIRC the DSC is triggered by accelerometers in the car, steering wheel position, and wheel speed sensors which are interpreted by the computer which decides that "you are in an understeer or oversteer" situation and brakes individual wheels/cuts engine power to get you back in control.

The mystery to me is does the LSD have a lower threshold of activation than the e diff? If you are theoretically going straight (no over or under steer going on) and one of the rear wheels hit a slippery patch of pavement (ice, snow, sand, gravel, lard etc.) while accelerating (as in overtaking) which kicks-in first, the LSD or the e-diff?
Anybody have any experience in trying this scenario?

BTW, I think e-diff is always on regardless of what setting you have on.

[moldcad]

Originally Posted by foamie

IIRC the DSC is triggered by accelerometers in the car, steering wheel position, and wheel speed sensors which are interpreted by the computer which decides that "you are in an understeer or oversteer" situation and brakes individual wheels/cuts engine power to get you back in control.

The mystery to me is does the LSD have a lower threshold of activation than the e diff? If you are theoretically going straight (no over or under steer going on) and one of the rear wheels hit a slippery patch of pavement (ice, snow, sand, gravel, lard etc.) while accelerating (as in overtaking) which kicks-in first, the LSD or the e-diff?
Anybody have any experience in trying this scenario?

BTW, I think e-diff is always on regardless of what setting you have on.

Just remember that:

- eDiff only works when DSC is OFF
- clutch-pack mechanical LSD like M-Performance one is torque-sensitive not wheel-slip speed sensitive

You will find your answer...

[tke743]

Originally Posted by moldcad

Are you driving with DSC OFF on such crappy roads as you describe? Because if you are so sure your eDiff works so great in the snow, slush, ice etc., you must be - with DSC on, eDiff doesn't work at all!

I'm afraid that this is accurate in the language but not the technology. Even with DSC ON the e-diff functionality is there, it just works differently. In the case with DSC OFF it is the ONLY part still on. It is acting like a LSD and no stability or traction controls. With the DSC ON it is still there, but is subjugated by the other nanny items. If it wasn't there, you could not get moving in conditions like this.

So we are now splitting hairs, but I can say that I have done both today. ON and OFF. In the ON setting the car has no problems getting started and keeping things straight. This is in near worst case conditions on the road. With it OFF (in a parking lot) it is a lot of fun. The e-diff only working lets you have fun and you can feel it working. It is quite good.

Back to the OP's original question. No you don't need a LSD to address bad roads in the winter. The car will address that without the LSD.

[foamie]

Originally Posted by moldcad

Just remember that:

- eDiff only works when DSC is OFF
- clutch-pack mechanical LSD like M-Performance one is torque-sensitive not wheel-slip speed sensitive

You will find your answer...

Oh, probably not
an e-diff system operates using the ABS sensors and the ABS system to control wheelspin AND so does the DSC (although it uses other inputs too and then the computer decides which wheels to brake and when to cut engine power) in an unstable situation.

If you think of it, what scenario would you like the e-diff to be OFF, if you do not have a LSD? There is NO situation as a auto enthusiast would you want this (except doing inefficient one-wheel-burnouts) because now you have a open differential and if the DSC software/hardware is not sophisticated enough to maintain DSC functionality, then NO DSC. Which is why I think that my BMW dealership in my location WOULD NOT turn off the e-diff when I was looking at a 135 coupe some years ago that I wanted to put an aftermarket LSD (liability concerns?). You can however turn-off DSC and still have the benefit of the e-diff (acting as a LSD).

There are lots of types of LSDs and if the M-Perf LSD option on the M235i is a clutch pack then it does not operate by being torque sensitive (Torsen differential but friction is still involved).

[quenotte]

BMW just explained how it works in M Perf diff press release : http://www.2addicts.com/forums/showthread.php?t=982939

[wjones14]

I come from a background of U.S. V8 manual RWD cars - Mustangs, Corvette, Camaro - all of which come with a mechanical LSD standard, aka "posi" rear end. So I have no experience with an e-Diff, and to be honest, am somewhat concerned about it since I track my car once per year or so.

For the record, I don't do burnouts, though I will shift hard into 2nd gear occasionally with my Mustang just to break the rear loose. Even with the Traction Control on, this will always leave two fat tire patches on the road, 10 feet long or so. (With TC off, the patches are much longer than 10 feet.)

My question is about the e-Diff in the M235i. If you do a burnout, will it leave two tire patches or one? Does it matter if you are in Comfort, Sport, or Sport+ mode?

[tke743]

Originally Posted by wjones14

My question is about the e-Diff in the M235i. If you do a burnout, will it leave two tire patches or one? Does it matter if you are in Comfort, Sport, or Sport+ mode?

Two. And that is in sport+ or DSC off. In the others, the nanny systems will stop it too quickly.

[wjones14]

Originally Posted by tke743

Two. And that is in sport+ or DSC off. In the others, the nanny systems will stop it too quickly.

It won't do a burnout at all in Sport mode?

[tke743]

Originally Posted by wjones14

It won't do a burnout at all in Sport mode?

Minimally, sport+ and DSC off are the hooligan modes.

[foamie]

Originally Posted by quenotte

BMW just explained how it works in M Perf diff press release : http://www.2addicts.com/forums/showthread.php?t=982939

Thanks

[moldcad]

Originally Posted by quenotte

BMW just explained how it works in M Perf diff press release : http://www.2addicts.com/forums/showthread.php?t=982939

And here is the excerpt from the above link that answers many of questions asked here, including my own (OP) main one:

"The unit reacts instantaneously to torque variances in the half-shafts. As such, the responsiveness of the unit operates before DSC has an opportunity to respond, thus no operational interference with the aforementioned "driving aids".

So - depending how close is the above design intent to real-life behavior, there is no reason why a non-tracking M235i owner should not be able to take full advantage of M-P LSD, even if he mostly drives with DSC ON.

[quenotte]

Yes I think that you have the point .

I've ask my local dealer a price quote for the M Performance LSD.

First they announced me 2834€ (excl VAT) retail price...

I found it at 2413€ (excl VAT) in Germany.

In the meantime I found ETK 12/2014 prices for M Performance Differential 33107555610:

33107555610000002567.23000000000.0016%* 1 000002156.470EUR

So 2156.47€ (excl VAT) corresponds to ~2560 USD, price generally observed in the US...