Does getting a LSD fix loss traction problem?

[TimMc]

McLaren uses an e-diff...

[sparoz]

Originally Posted by TimMc

McLaren uses an e-diff...

But it is only a part of a greater system that works together unlike the BMW isolated system.

[Jeef Beef]

Originally Posted by TimMc

McLaren uses an e-diff...

Different from our one, it actively shifts power from wheel to wheel if I'm not mistaken?

Kinda like the vectoring diffs in Audis, the X6 etc.

[TimMc]

Originally Posted by Jeef Beef

Different from our one, it actively shifts power from wheel to wheel if I'm not mistaken?

Kinda like the vectoring diffs in Audis, the X6 etc.

Not the way I read it, but you may well be right.

[timbo_3101]

Originally Posted by TimMc

I disagree with your last point here Ian. Having being partially bogged off the track at Lakeside I was spinning both wheels & making slow progress back to the bitumen. I think if I was just spinning one wheel (& getting no drive to the other) I would've found it harder/impossible to get out.

Sorry to interject because I think you guys are both regulars on track. However this initial loss of traction when going onto grass/mud/sand is probably due to hot (sticky) tyres and adherent debris ...

[TimMc]

Originally Posted by timbo_3101

Sorry to interject because I think you guys are both regulars on track. However this initial loss of traction when going onto grass/mud/sand is probably due to hot (sticky) tyres and adherent debris ...

and the wet grass & mud…
Actually, if in fact the late Barry Sheene was correct, when you get off onto wet grass you actually accelerate. NASA & ESA should utilise this property, as should CERN.

[Jeef Beef]

Very interesting read here from the main forum, with datalogs to back up his conclusions. http://www.1addicts.com/forums/showthread.php?t=719012

Originally Posted by int2str

I'd like to dis-spell some rumors and clear up some misconceptions regarding BMWs electronically controlled differential or as some call it the "electronic LSD".

The BMW 1-series as well as many other recent BMW models feature an electronically controlled Automatic Differential Brake (ADB) system, that in conjunction with a normal open rear differential works to emulate a traditional mechanical limited slip system.

Below are some questions I've compiled based on forum posts I've found here. Feel free to ask more questions and I'll update this FAQ periodically.

All these answers are from my personal experience and to the best of my knowledge. I reserve the right to make corrections as better information becomes available.

----

Does the 1-series (or other recent BMWs) have an open rear differential?

Mechanically, the answer is yes - there is a completely open rear differential between the two rear wheels. This open diff is however assisted by an automatic differential braking system that will apply resistance to one wheel to equalize traction between the two wheels.


What does that look like in action?

Here's a graph showing the on-board telemetry of a 135i during an autocross run going around a left hand corner:


The light blue line shows braking force applied to the left (inside) rear wheel and the yellow line shows braking force applied to the right (outside) rear wheel. Dark blue shows the throttle pedal position and the red line show the brake pedal.

As you can see, without any brake pedal applied, the car applies some light brake pressure to the inside (less loaded) rear wheel to prevent wheel spin.

Also note that when the brake pedal *is* actually pressed, the car still manages the left/right brake balance to keep the car as neutral as possible under braking.

This car was equipped with a mechanical LSD as well - so even with a mechanical LSD, the system still provides additional inputs.


If I loose traction, will only 1 wheel spin?

No. The system automatically applies brake pressure to the wheel with the least amount of traction to get both wheels spinning.


Does the system reduce engine power?

No. Brake pressure is applied to one wheel, the engine power is not affected.


Will the braking force lock up the wheel or slow me down?

No. Only light brake pressure is applied to the spinning wheel this does not slow the car down. Mechanical limited slip differentials perform the exact same function, though instead of using the brakes to apply friction on the spinning wheel, mechanical friction is applied inside the differential.


Does this system interfere even if I'm not smoking tires?

Yes. The electronic differential braking acts even if you're not lighting up tires to help stabilize the car in a variety of situations.


Can I turn this system off?

No. Even with all traction and stability control (DTC and DSC) turned off, differential braking is still enabled.


Can I drift with the only the electronic differential?

Yes, absolutely!


Do I still need a mechanical LSD then?

Maybe. This is a tough question to answer and a personal one at that.

The electronically assisted differential works rather well actually. It puts power down to both wheels, allows drifting and generally provides a positive driving feedback and control.

However, the electronic system has it's limits. Once traction loss is too great, the system can be overwhelmed, causing a more sudden loss in traction than what a mechanical differential would do. In other words, you might spin more suddenly than with a mechanical diff. Also, the electronic control does not provide the same feedback to the driver and the same confidence that a mechanical differential does. Thus controlling the car is more difficult than it would be with a mechanical diff.

Ultimately, there is no huge difference in traction availability between the mechanical and electronic differentials. The biggest difference is in the way the car "feels". This is mostly evident exiting corners under heavy throttle. This is where the mechanical differential shines.

Because the differential system uses your brakes to aid traction, excessive heat and wear may be generated on your rear brakes during track driving. A mechanical LSD can help reduce this.


Do I need a mechanical LSD for....

... daily driving? No.

... "spirited" canyon driving? No. If you're regularly overwhelming the electronic differential on public roads, please start autocrossing or track driving your car instead.

... drag racing? Maybe. The electronic differential is very good providing straight line traction. A mechanical LSD is likely not going to make a big difference here. On the highest levels of the sport, maybe an LSD would make a difference. At that point you may be better off with a locking one instead though.

... track/autocross? Maybe. BMW's differential braking system works rather well even for autocrossing or track driving. Don't be afraid to track/autocross your car in stock trim. A mechanical differential will make a big difference in controllability and confidence here so there is a definite benefit for track junkies and autocrossers.

... drifting events? Most likely. More control = better drifts.

and then his own summary

Originally Posted by int2str

The intend of this thread was not to discuss the subtleties regarding ADB vs. LSD and which is better, but simply to clarify some common misconceptions.

To summarize:
- The 135i and other recent BMWs have an electronically assisted open differential that is significantly better than an open differential.

- Modern BMWs put power down to both wheels in most situation.

- No power is cut as a result of ADB.

- The electronic differential system works well for the vast majority of BMW owners and in most scenarios.

[Jeef Beef]

So to answer the OP's question,

drag racing? Maybe. The electronic differential is very good providing straight line traction. A mechanical LSD is likely not going to make a big difference here.

[MrBlonde]

I told you so :-)

[MrBlonde]

Originally Posted by Ian///M

IMO e-diff is good enough for 95% of driving. On a track a mechanical LSD will definitely be beneficial which is why ///M cars all have LSD's.

It will be very difficult to drift without a LSD

I think Peter hit it on the head. These cars should come with a mechanical LSD and adding one to your 135 can only be a good thing. But you don't need one unless you are circuit racing.

I think Advan will have some interesting ideas about how to get a great LSD setup on your 335 or 135 in the near future.

[Jeef Beef]

Originally Posted by MrBlonde

I told you so :-)

Originally Posted by Ian///M

IMO e-diff is good enough for 95% of driving. On a track a mechanical LSD will definitely be beneficial which is why ///M cars all have LSD's.

It will be very difficult to drift without a LSD

Originally Posted by MrBlonde

I think Peter hit it on the head. These cars should come with a mechanical LSD and adding one to your 135 can only be a good thing. But you don't need one unless you are circuit racing.

I think Advan will have some interesting ideas about how to get a great LSD setup on your 335 or 135 in the near future.

That being said, I still want one for my car due to the occasional track days, more predictable behaviour from the rear end and the ability to hang the tail out with more control

There are a few videos in the above thread with guys drifting their stock 135i's without much drama. Still, the eLSD is more of a reactive rather than proactive system so it makes it harder.

That doesn't mean it's a totally reactive system however, the logs from the post show that braking force is gradually applied to the inside wheel REGARDLESS of whether there is traction loss or not. It seems like the system is more intuitive than we give credit for.

[TimMc]

Originally Posted by MrBlonde

I think Peter hit it on the head. These cars should come with a mechanical LSD and adding one to your 135 can only be a good thing. But you don't need one unless you are circuit racing.

Or want to get up your driveway

Originally Posted by Jeef Beef

That being said, I still want one for my car due to the occasional track days, more predictable behaviour from the rear end and the ability to hang the tail out with more control

There are a few videos in the above thread with guys drifting their stock 135i's without much drama. Still, the eLSD is more of a reactive rather than proactive system so it makes it harder.

That doesn't mean it's a totally reactive system however, the logs from the post show that braking force is gradually applied to the inside wheel REGARDLESS of whether there is traction loss or not. It seems like the system is more intuitive than we give credit for.

E-diff doesn't cope on track. Too easy to spin up the inside wheel - but still cook your rear brakes as the e-diff tries in vain to stop the spinning. In my experience.

[Jeef Beef]

Originally Posted by TimMc

Or want to get up your driveway

E-diff doesn't cope on track. Too easy to spin up the inside wheel - but still cook your rear brakes as the e-diff tries in vain to stop the spinning. In my experience.

This I'm familiar with. I had to replace my rear brakes at around 25,000km, the few track days I threw in had something to do with it.

Btw OCC arrived last monday, thanks heaps

[1q2w3e4r]

Originally Posted by Ian///M

As with sportsbikes, and LSD is crucial for the track

How do you have an LSD in a sportbike?

[TimMc]

Originally Posted by Ian///M

As with sportsbikes, and LSD is crucial for the track

Originally Posted by 1q2w3e4r

How do you have an LSD in a sportbike?

Yeah, he's lost me there. And I used to track my bike.

[TimMc]

Originally Posted by Jeef Beef

Btw OCC arrived last monday, thanks heaps

Cool. I'd forgotten about that.

[Stuart@BMRAutowerkes]

Originally Posted by Ian///M

The 135/335i should have come with a LSD in stock form

But then the M boys wouldn't have anything to gloat about.

Originally Posted by Ian///M

IMO e-diff is good enough for 95% of driving. On a track a mechanical LSD will definitely be beneficial which is why ///M cars all have LSD's.

It will be very difficult to drift without a LSD

Yes agree, e-diff served me fine 95% of the time.

I'm still really surprised at how easy it is to lose the rear-end now that I have an LSD.

I'm going to wakefield tomorrow so will be able to appreciate the diff there

[MrBlonde]

Originally Posted by TimMc

Or want to get up your driveway

Hee hee. Funny as it is, it's always the first situation I notice an LSD or lack thereof in a new car!

[koastal]

Originally Posted by Jeef Beef

This I'm familiar with. I had to replace my rear brakes at around 25,000km, the few track days I threw in had something to do with it.

Btw OCC arrived last monday, thanks heaps

Crickey !! I have 56k on mine and the original rear brake pads are still pretty good. Have done a couple oftrack days to, maybe haven't been punting it hard enough, or perhaps it doesn't activate as much when the nannies are of.

[Jeef Beef]

Originally Posted by koastal

Crickey !! I have 56k on mine and the original rear brake pads are still pretty good. Have done a couple oftrack days to, maybe haven't been punting it hard enough, or perhaps it doesn't activate as much when the nannies are of.

The eLSD works regardless of whether the nannies are on or off, plus on track days my nannies are off anyway. And also on the road when there's good weather and I want to give it a bootfull....

Are you running a tune on your car? Extra power might be what's causing mine to activate so often.

[koastal]

[QUOTE=Jeef Beef;12385300]The eLSD works regardless of whether the nannies are on or off, plus on track days my nannies are off anyway. And also on the road when there's good weather and I want to give it a bootfull....

Are you running a tune on your car? Extra power might be what's causing mine to activate so often.[/

Yes it has a jb4 and downpipe. Not sure how much power it makes as it has never been on a dyno. Terminal speed at the drag strip is 113 mph

Maybe I need to drive it harder. What sort of times have been getting at the track ?
Cheers