[munchen1]

The biggest omission in the updated 3 series is the missing electronic locking differential as found on the new 7 and the John Cooper Mini. I assume hardware costs are minimal, and the 3 desperately needs this for safety reasons (take it for a ride in the snow), but it seems obvious that they don't want the 335 to have a differential because it would bridge the gap with the under-torqued M3 and cannibalize sales. So it looks like product differentiation tops safety.

[Lassaxi]

Welcome to the forum.

This is going to be a long post because it is going to take a few minutes to explain how all these different systems work. The Electronic Differential Lock control ("EDL") on the Mini you described is not an actual locking differential like a true limited slip differential ("LSD") would be. Rather, it is very similar to BMW's DSC system, which uses an open differential with individual wheel braking to redistribute torque among the driven wheels.

In a car with a open differential, the driven wheels always receive the same amount of torque, no matter what. A slipping wheel needs less torque to spin. Thus, when one wheel is on ice, it takes very little torque to get that wheel to spin fast. The problem is that the other wheel, which is presumably on dry land, needs more torque to spin because it has a lot of friction to overcome. In a car with an open differential, like our 3ers, the amount of torque that will go to each wheel is the lowest common denominator, i.e., the smallest amount of torque that either wheel needs to move. Put another way, because the amount of torque needed to move the spinning wheel is very small, only a very small amount of torque will be sent to the wheel with traction, and you won't go anywhere.

There are two basic ways to fix this problem. One is with an LSD. With a typical locking LSD, the differential itself is designed to lock mechanically so that more torque can be sent to the non-slipping wheel. Other types of LSDs, such as Torsen differentials, are fundamentally open differentials that have a special torque multiplying gear, which allows the diff to send a multiple of the spinning wheel's torque to the other wheel.

The second way to solve this problem is to increase the lowest common denominator by increasing the amount of torque the spinning wheel needs to get moving. The way you do that is by applying the brakes to the spinning wheel. By applying the brakes, you increase the amount of torque needed to make the spinning wheel spin, and you thus increase the amount of torque that the open diff can send to the non-spinning wheel (because both wheels will receive the same amount of torque).

DSC, which is BMW's Dynamic Stability Control system, solves the slip problem the second way. When one wheel on a given axle slips, DSC intervenes applies he brakes to the spinning wheel, which sends more power to the other wheel, which hopefully has more grip. DSC also intervenes by braking wheels and/or cutting engine power to correct over- and understeer when it detects that the car is traveling on an unintended path. This is a very conservative way to solve traction-related safety problems, because it works by slowing the car down and bringing it back within its handling limits.

Many members here are familiar with DTC, which is a sub-program of the DSC system. In DTC (Dynamic Traction Control) mode, the yaw rate sensors are inactive, and the computer will not intervene to correct over and understeer (at least not per se). However, it will still intervene with wheel braking and/or cutting engine power when it detects wheelspin. However, because DTC mode is optimized for driving in heavy snow, where some wheelspin is desirable to keep up forward momentum, DTC will also allow the wheels to spin longer (as compared with DSC mode) before it intervenes.

In a 3er, you can turn DSC and DTC off altogether. When that happens, there are no interventions, and you are on your own. In the Mini, that's not the end of the story. Even with DSC off, there is still an EDL function, which is essentially a very limited mode of DSC that is designed to help improve high-speed cornering.

During high speed cornering there is more force placed on the outside wheel which can lead to the inside wheel breaking traction, resulting in no forward drive. This can lead to instability and is potentially dangerous. If the car had an LSD, the LSD would shift more torque to the outside wheel, which would let the driver steer through the turn with the accelerator.

EDL does something similar, but using the brakes. During high speed cornering, EDL brakes the inside wheel when it starts to lose traction. This causes the open differential to send more torque to the outside wheel, just like an LSD would. EDL doesn't react as fast as an LSD would, but it is probably better than nothing. To be sure, DSC will eventually do the same thing, but the EDL "mode" of operation is somewhat less intrusive. For example, EDL only intervenes by applying the brakes to one wheel- it does not, for instance, cut engine power. You can still lose control of the car in EDL mode, just like you can with an LSD, if you drive past the handling limits, and EDL won't fight very hard to bring you back. In contrast, if you approach the car's handling limit with DSC fully active, the computer will try to slow you down so that you don't lose control.

So, as you can see, the issue is not safety but performance. DSC and DTC will ensure that the car stays safe, but they're not optimal for performance driving. EDL is better for performance driving, but still not as good as an LSD.

[Jobu]

nice explanation

[Autobot]

WOW, that's great info for all of us, Thanks

[nicknaz]

OP, i noticed in your sig you have a 330i. In my 328 with OE sport package tires I notice that even with a very hard launch the tires barely chirp. I suspect that BMW omitted the LSD because 220 or 200ft lb of torque can be handled by the 255mm wide tires easily enough.

As long as you exercise some measure of throttle control in your 330 I think you are just fine without a LSD, and there are only very specific corner types (very low speed, leading into straight) that would benefit from LSD (such as T11 at t-hill). In the faster stuff I don't think the open diff is slowing you down much, if at all

Re the 335, it was never meant to be a hardcore enthusiast car IMHO, since the cooling system is insufficient for an experience track user. For more novice users the at the limit handling characteristics of the open diff (one wheel spin instead of potential big power oversteer) is much safer anyway

[Revlis]

Originally Posted by Nick Nazareno

OP, i noticed in your sig you have a 330i. In my 328 with OE sport package tires I notice that even with a very hard launch the tires barely chirp. I suspect that BMW omitted the LSD because 220 or 200ft lb of torque can be handled by the 255mm wide tires easily enough.

As long as you exercise some measure of throttle control in your 330 I think you are just fine without a LSD, and there are only very specific corner types (very low speed, leading into straight) that would benefit from LSD (such as T11 at t-hill). In the faster stuff I don't think the open diff is slowing you down much, if at all

Re the 335, it was never meant to be a hardcore enthusiast car IMHO, since the cooling system is insufficient for an experience track user. For more novice users the at the limit handling characteristics of the open diff (one wheel spin instead of potential big power oversteer) is much safer anyway

Umm...WHAT? 335 Cooling system plenty sufficient "experienced" track user or not, I believe it was the Lack of the Oil cooler in the Automatics only that was an issue.

[Arustik1]

Originally Posted by Lassaxi

Welcome to the forum.

This is going to be a long post because it is going to take a few minutes to explain how all these different systems work. The Electronic Differential Lock control ("EDL") on the Mini you described is not an actual locking differential like a true limited slip differential ("LSD") would be. Rather, it is very similar to BMW's DSC system, which uses an open differential with individual wheel braking to redistribute torque among the driven wheels.

In a car with a open differential, the driven wheels always receive the same amount of torque, no matter what. A slipping wheel needs less torque to spin. Thus, when one wheel is on ice, it takes very little torque to get that wheel to spin fast. The problem is that the other wheel, which is presumably on dry land, needs more torque to spin because it has a lot of friction to overcome. In a car with an open differential, like our 3ers, the amount of torque that will go to each wheel is the lowest common denominator, i.e., the smallest amount of torque that either wheel needs to move. Put another way, because the amount of torque needed to move the spinning wheel is very small, only a very small amount of torque will be sent to the wheel with traction, and you won't go anywhere.

There are two basic ways to fix this problem. One is with an LSD. With a typical locking LSD, the differential itself is designed to lock mechanically so that more torque can be sent to the non-slipping wheel. Other types of LSDs, such as Torsen differentials, are fundamentally open differentials that have a special torque multiplying gear, which allows the diff to send a multiple of the spinning wheel's torque to the other wheel.

The second way to solve this problem is to increase the lowest common denominator by increasing the amount of torque the spinning wheel needs to get moving. The way you do that is by applying the brakes to the spinning wheel. By applying the brakes, you increase the amount of torque needed to make the spinning wheel spin, and you thus increase the amount of torque that the open diff can send to the non-spinning wheel (because both wheels will receive the same amount of torque).

DSC, which is BMW's Dynamic Stability Control system, solves the slip problem the second way. When one wheel on a given axle slips, DSC intervenes applies he brakes to the spinning wheel, which sends more power to the other wheel, which hopefully has more grip. DSC also intervenes by braking wheels and/or cutting engine power to correct over- and understeer when it detects that the car is traveling on an unintended path. This is a very conservative way to solve traction-related safety problems, because it works by slowing the car down and bringing it back within its handling limits.

Many members here are familiar with DTC, which is a sub-program of the DSC system. In DTC (Dynamic Traction Control) mode, the yaw rate sensors are inactive, and the computer will not intervene to correct over and understeer (at least not per se). However, it will still intervene with wheel braking and/or cutting engine power when it detects wheelspin. However, because DTC mode is optimized for driving in heavy snow, where some wheelspin is desirable to keep up forward momentum, DTC will also allow the wheels to spin longer (as compared with DSC mode) before it intervenes.

In a 3er, you can turn DSC and DTC off altogether. When that happens, there are no interventions, and you are on your own. In the Mini, that's not the end of the story. Even with DSC off, there is still an EDL function, which is essentially a very limited mode of DSC that is designed to help improve high-speed cornering.

During high speed cornering there is more force placed on the outside wheel which can lead to the inside wheel breaking traction, resulting in no forward drive. This can lead to instability and is potentially dangerous. If the car had an LSD, the LSD would shift more torque to the outside wheel, which would let the driver steer through the turn with the accelerator.

EDL does something similar, but using the brakes. During high speed cornering, EDL brakes the inside wheel when it starts to lose traction. This causes the open differential to send more torque to the outside wheel, just like an LSD would. EDL doesn't react as fast as an LSD would, but it is probably better than nothing.

So, as you can see, the issue is not safety but performance. DSC and DTC will ensure that the car stays safe, but they're not optimal for performance driving. EDL is better for performance driving, but still not as good as an LSD.

[Roowah]

Very well said. Thank you for taking the time to explain this.

[achien]

Our drivers today suck, if you are looking to speed through the corners, you shouldn't be expecting any "gadgets" to bail you out of trouble...

The old folks never had any ABS, DSC, DTC, LSD, EDL, (or ABCs, blah blah blah) and they have done pretty well.

Improve your driving skills & techniques first!

Originally Posted by munchen1

The biggest omission in the updated 3 series is the missing electronic locking differential as found on the new 7 and the John Cooper Mini. I assume hardware costs are minimal, and the 3 desperately needs this for safety reasons (take it for a ride in the snow), but it seems obvious that they don't want the 335 to have a differential because it would bridge the gap with the under-torqued M3 and cannibalize sales. So it looks like product differentiation tops safety.

[galahad05]

Ummm...

No LSD? Then why did my 1968 Corvette come with one--stock?

Heck, just check out any 1960's musclecar, sports car, whatever.


LSDs first came on the scene for automobiles back in 1935 (Porsche)...
http://en.wikipedia.org/wiki/Limited_slip_differential

[visor]

Originally Posted by galahad05

Ummm...

No LSD? Then why did my 1968 Corvette come with one--stock?

Heck, just check out any 1960's musclecar, sports car, whatever.


LSDs first came on the scene for automobiles back in 1935 (Porsche)...
http://en.wikipedia.org/wiki/Limited_slip_differential

For better comparison, older gen 3 series did come with a true mechanical LSD. For reasons of cost and fuel economy, I suppose, the newer gen has been using electronic braking via ABS to simulate the LSD. Not the same I know, but for 99.999% of those people who purchase the 3 series, I'd bet they won't drive it to the limit enough to know/appreciate the difference.

[Brian-313]

Very nice write ...

[visor]

Oh yeah, in answer to the OP,

Yes, the 335i with all its power would definitely benefit from an LSD! Even if it came as a $2500 option, I would definitely pay for it. But that would make it (almost) beat up the E46 M3, so here we are...

[nicknaz]

Originally Posted by Revlis

Umm...WHAT? 335 Cooling system plenty sufficient "experienced" track user or not, I believe it was the Lack of the Oil cooler in the Automatics only that was an issue.

Check out the Track section of this forums. Some 335 users are skipping track days because of high ambient temperatures, others with stock tune, manual trans and oil cooler experience 'limp mode' every track session, and many report 290F as the operating temperature of the oil during hard use (that's stupidly high).

I'm not trying to suggest the 335 is 'bad', I'm just pointing out that, in my opinion, insufficient (oil) cooling for hard use points to the fact that the 335 was designed with the typical street user in mind, not the experienced heavy track user.

just my $0.02, no need to get worked up over it

[galahad05]

A little history: I've never driven a car without a limited-slip diff until my last two cars--a Toyota and now the 335.

Yes, in skilled/experienced hands the LSD can really increase performance (versus a plain old open diff with no electronic braking help)...

-BUT-

You can also get yourself into a world of trouble with an LSD if you aren't experienced or are just having an off day. We're talking spinouts, leaving the road ass-backwards, major emergency-condition fishtailing, etc.


LSDs aren't for everyone.

[visor]

Originally Posted by galahad05

You can also get yourself into a world of trouble with an LSD if you aren't experienced or are just having an off day. We're talking spinouts, leaving the road ass-backwards, major emergency-condition fishtailing, etc.


LSDs aren't for everyone.

I'm sure LSD with DSC, if not disabled, would be helpful in those instances.

For example, Porsches with LSD has their version of DSC.

[galahad05]

You're almost certainly right, though I can't tell from experience: My very very first car with stability control was this 335 I'm driving now.

[Two Sheds]

Originally Posted by Lassaxi

This is going to be a long post because it is going to take a few minutes to explain how all these different systems work. The Electronic Differential Lock control ("EDL") on the Mini you described is not an actual locking differential like a true limited slip differential ("LSD") would be. Rather, it is very similar to BMW's DSC system, which uses an open differential with individual wheel braking to redistribute torque among the driven wheels.

Are you talking about the differential that comes as standard on a mini? In Canada there is a stand alone option (around $500 I think) for an LSD which I assume is a proper LSD.

[Lassaxi]

Originally Posted by Two Sheds

Are you talking about the differential that comes as standard on a mini? In Canada there is a stand alone option (around $500 I think) for an LSD which I assume is a proper LSD.

I am talking about the Electronic Differential Lock Control system, which I believe is what the OP was referring to. It'll be available in the US on most Minis starting with the 12/08 build. You are correct that a true LSD is also optional.

[demosthenes]

Great posts Lassaxi. Thanks.

[wilkoal]

This thread is very a good one and Lassaxi explanation is excellent.

However is anyone able to get "smooth" drifting while cornering taking advange of the Electronic Differential Lock (clearly with DSC off) like in this video

.

I tried several times on dry conditions but the car reactions are very harsh (if not scaring)...got the car oversteering from one side to the other fishtailing.

I guess this is why a LSD is so claimed to be important.

[Cyber]

Originally Posted by Lassaxi

Welcome to the forum.

This is going to be a long post because it is going to take a few minutes to explain how all these different systems work. The Electronic Differential Lock control ("EDL") on the Mini you described is not an actual locking differential like a true limited slip differential ("LSD") would be. Rather, it is very similar to BMW's DSC system, which uses an open differential with individual wheel braking to redistribute torque among the driven wheels.

In a car with a open differential, the driven wheels always receive the same amount of torque, no matter what. A slipping wheel needs less torque to spin. Thus, when one wheel is on ice, it takes very little torque to get that wheel to spin fast. The problem is that the other wheel, which is presumably on dry land, needs more torque to spin because it has a lot of friction to overcome. In a car with an open differential, like our 3ers, the amount of torque that will go to each wheel is the lowest common denominator, i.e., the smallest amount of torque that either wheel needs to move. Put another way, because the amount of torque needed to move the spinning wheel is very small, only a very small amount of torque will be sent to the wheel with traction, and you won't go anywhere.

There are two basic ways to fix this problem. One is with an LSD. With a typical locking LSD, the differential itself is designed to lock mechanically so that more torque can be sent to the non-slipping wheel. Other types of LSDs, such as Torsen differentials, are fundamentally open differentials that have a special torque multiplying gear, which allows the diff to send a multiple of the spinning wheel's torque to the other wheel.

The second way to solve this problem is to increase the lowest common denominator by increasing the amount of torque the spinning wheel needs to get moving. The way you do that is by applying the brakes to the spinning wheel. By applying the brakes, you increase the amount of torque needed to make the spinning wheel spin, and you thus increase the amount of torque that the open diff can send to the non-spinning wheel (because both wheels will receive the same amount of torque).

DSC, which is BMW's Dynamic Stability Control system, solves the slip problem the second way. When one wheel on a given axle slips, DSC intervenes applies he brakes to the spinning wheel, which sends more power to the other wheel, which hopefully has more grip. DSC also intervenes by braking wheels and/or cutting engine power to correct over- and understeer when it detects that the car is traveling on an unintended path. This is a very conservative way to solve traction-related safety problems, because it works by slowing the car down and bringing it back within its handling limits.

Many members here are familiar with DTC, which is a sub-program of the DSC system. In DTC (Dynamic Traction Control) mode, the yaw rate sensors are inactive, and the computer will not intervene to correct over and understeer (at least not per se). However, it will still intervene with wheel braking and/or cutting engine power when it detects wheelspin. However, because DTC mode is optimized for driving in heavy snow, where some wheelspin is desirable to keep up forward momentum, DTC will also allow the wheels to spin longer (as compared with DSC mode) before it intervenes.

In a 3er, you can turn DSC and DTC off altogether. When that happens, there are no interventions, and you are on your own. In the Mini, that's not the end of the story. Even with DSC off, there is still an EDL function, which is essentially a very limited mode of DSC that is designed to help improve high-speed cornering.

During high speed cornering there is more force placed on the outside wheel which can lead to the inside wheel breaking traction, resulting in no forward drive. This can lead to instability and is potentially dangerous. If the car had an LSD, the LSD would shift more torque to the outside wheel, which would let the driver steer through the turn with the accelerator.

EDL does something similar, but using the brakes. During high speed cornering, EDL brakes the inside wheel when it starts to lose traction. This causes the open differential to send more torque to the outside wheel, just like an LSD would. EDL doesn't react as fast as an LSD would, but it is probably better than nothing. To be sure, DSC will eventually do the same thing, but the EDL "mode" of operation is somewhat less intrusive. For example, EDL only intervenes by applying the brakes to one wheel- it does not, for instance, cut engine power. You can still lose control of the car in EDL mode, just like you can with an LSD, if you drive past the handling limits, and EDL won't fight very hard to bring you back. In contrast, if you approach the car's handling limit with DSC fully active, the computer will try to slow you down so that you don't lose control.

So, as you can see, the issue is not safety but performance. DSC and DTC will ensure that the car stays safe, but they're not optimal for performance driving. EDL is better for performance driving, but still not as good as an LSD.

Wow