I have some questions about the Electronic LSD and the DSC/DTC.

Does anyone know how the electronic LSD works and when it works in a 335? I've been told that it only works when the DTC is on and when traction control is off it doesn't work at all. The same person told me that when it is working it tries to put power to the lightest wheel.

Is it true that the DTC uses only brake brakes for traction control and not the power? I understand that the DTC reverts to DSC if the car experiences more then 0.4 Gs. True?

If I want the best performance from my stock 335 on the track what should I do with traction control considering all of the above: DTC on or traction control completely off?

Thanks for your time.

ask "azhrei", he seems to have some applicable experience.

Electronic LSD - :rofl

Your BMW is limiting throttle and or individual braking to keep your car going in it's intended direction.

The car does not swith back to DSC if it detects too many G's if the system has been disengaged.

FOr track days, hold the button down for a couple seconds to turn *most* of it off.

What's to laugh about? you act like someone made that up, are you really that ignorant? There is such a thing as electronic LSD, and it provides the same result as clutch based LSD. In fact, there are at least five different types of LSD. You purists really need to do some research. Most people I guess see it as just braking the tire that's spinning out of control, and they don't understand how an open diff works and how braking the loose tire actually causes torque to be applied to the other tire.

Electronic limited slip differential system uses Anti-lock brake (http://en.wikipedia.org/wiki/Anti-lock_brake) sensors and hardware to electronically monitor wheel speed. If one of the wheels on an axle is rotating faster, computer briefly applies brakes to it, slowing the spinning wheel down and causing the wheel on the opposite end of an open differential to start spinning and gain traction. This is an opposite to the anti-lock brake application, when a locked wheel is electronically released.


One advantage of this system over mechanical is that the vehicle steering and control is less affected. It also generates less stress on the drivetrain compared to a mechanical locking device, making it particularly suitable for the vehicles with independent suspension (http://en.wikipedia.org/wiki/Independent_suspension). It can also be tuned for specific applications off- and on road and a different speeds.
It's probably another Bose vs tube amp debate, a religious battle.

I'm not going to beat a dead horse, as this has been covered many times. At this point in technology, an "electronic" LSD cannot compare to a mechanical unit.

Which kind of mechanical unit does it not compare to? Helical, clutch? I might agree with a helical setup, but where the clutch version simply locks the two sides to spin at the same rate you're getting essentially the same thing with eLSD. The eLSD isn't quite as good for drifting, however, but it's still quite competent at limiting the rotational difference between tires.

I agree that it may not be the best setup for racing, but some people seem to treat it like there's no LSD at all, and that just bothers me as it's simply not true. They need to crack a book or two and rethink that.

Ok. So my question has spawned a debate. That can be interesting but I would still like to know when the eLSD works (DSC, DTC and/or all traction control off) and when it works does it try to drive the heavier wheel?

I suppose depending on the answer I'll be able to tell which setting would be the most advantageous, i.e.: if it works with all traction control off then hat would be the best setting. If it only works with DSC or DTC on then DTC might be the best setting.

From everything I've heard at the track a mechanical LSD is the way to go but my car doesn't have one and I'm not gonna spend 3500 on one. I hope the eLSD works with traction control off so I can learn more about driving without the car's assistance.

The user I mentioned above has done quite a bit of on track testing, they should be able to provide some real world experiences/explanations.

Sor, Thank you. I'll PM them.

I agree that it may not be the best setup for racing, but some people seem to treat it like there's no LSD at all, and that just bothers me as it's simply not true. They need to crack a book or two and rethink that.

LSD = Limited Slip Differential. There is no LSD. Open that diff and you will find that it is an open one.

What BMW did is to attempt to mimick an LSD by applying brake to the slipping wheel. For occasional use (like some ice/snow/mud) it's not a bad alternative. However, for any kind of aggressive driving (be it track days or your local canyon) this Virtual Limited Slip Light (VSL!) can have drawbacks. For one, it'll kill the life of the rear brakes. Second, what happens when the rear brakes overheat? VSL fades away. Last, the point of hard accelerating out of a corner is to, well, accelerate! Throwing out an anchor on the opposite wheel is hardly a way to achieve that goal.

It's better than nothing for sure. And it has the advantage of not worrying about diff clutch wear. But for the 'ultimate driving machine' it's hardly the ideal solution.

-Dave

LSD = Limited Slip Differential. There is no LSD. Open that diff and you will find that it is an open one.

What BMW did is to attempt to mimick an LSD by applying brake to the slipping wheel. For occasional use (like some ice/snow/mud) it's not a bad alternative. However, for any kind of aggressive driving (be it track days or your local canyon) this Virtual Limited Slip Light (VSL!) can have drawbacks. For one, it'll kill the life of the rear brakes. Second, what happens when the rear brakes overheat? VSL fades away. Last, the point of hard accelerating out of a corner is to, well, accelerate! Throwing out an anchor on the opposite wheel is hardly a way to achieve that goal.

It's better than nothing for sure. And it has the advantage of not worrying about diff clutch wear. But for the 'ultimate driving machine' it's hardly the ideal solution.

-Dave

That's the problem right there. People mistakenly think of LSD as a device (and specifically clutch based even though helical is supposedly superior). It isn't. It's a concept. A limited slip differential simply means you're limiting the difference in rotational speed between the tires. That's it. There are multiple ways to provide LSD, and they're all physical means of routing torque from the tire that slips to the one that grips. not sure why any method that provides this would only be considered virtual. I suppose a clutch based LSD is a virtual helical LSD because it doesn't use the same means to provide limited slip.

That's the problem right there. People mistakenly think of LSD as a device (and specifically clutch based even though helical is supposedly superior). It isn't. It's a concept. A limited slip differential simply means you're limiting the difference in rotational speed between the tires. That's it. There are multiple ways to provide LSD, and they're all physical means of routing torque from the tire that slips to the one that grips. not sure why any method that provides this would only be considered virtual. I suppose a clutch based LSD is a virtual helical LSD because it doesn't use the same means to provide limited slip.


So you're saying wearing out brakes is the same as a true LSD, lol. Me think not. From what I've found is that the open diff has some real trouble with rippled pavement. Where as a mechanical LSD is always active, an electronic is reactive. My "traction control" has come on repeatedly on smooth surfaces going straight, where the diff unloads over a bump. A mechanical diff wouldn't have caused the system to be activated.


Mechanical > Electronic

That's the problem right there. People mistakenly think of LSD as a device (and specifically clutch based even though helical is supposedly superior). It isn't. It's a concept. A limited slip differential simply means you're limiting the difference in rotational speed between the tires. That's it. There are multiple ways to provide LSD, and they're all physical means of routing torque from the tire that slips to the one that grips. not sure why any method that provides this would only be considered virtual. I suppose a clutch based LSD is a virtual helical LSD because it doesn't use the same means to provide limited slip.

No it's not. Limited Slip Differentials refer to mechanical means to distribute power to the proper wheel. REAL LSDs has clutches or viscous packs that mechanically alter the force being distributed via the differential. Open diff designs like what BMW puts on the none Ms, allow ALL the power to go to the open, or slipping wheel. Result is, on an LSD the power is re-distributed, while on an open diff, all available drive power goes to the slipping wheel therefore making the slipping worse. BMW attempts to "simulate" the effect of an LSD with DTC, where it brakes the wheel that's slipping to force power to be re-distributed back to the whee that's not slipping.

LSD is not a "concept." LSD allow you to put power to the wheel that's not slipping, while BMW's DTC BRAKES the wheel that is...Big difference when you try powering out of a tight corner or when you're driving on slippery surface.

Read up.

http://auto.howstuffworks.com/differential2.htm

http://auto.howstuffworks.com/differential4.htm

That's the problem right there. People mistakenly think of LSD as a device (and specifically clutch based even though helical is supposedly superior). It isn't. It's a concept. ......

You are correct only if wish to refer to the BMW implementation as a limited slip process. The actual, real, physical 'differential' (the 'D' in LSD) is an open one. Now, the type of LSD can vary - it can be clutch based or helical based, but the means to limit slip (the 'LS' in LSD) is purely mechanical.

To imply that the 335i has an LSD only serves to confuse. It simulates a true LSD, but it does not contain one.

-Dave

I am new to the world of the 335i and interested in some minor modifications on my ride. Is there a reliable aftermarket mechanical, helical LSD that exists to replace the "virtual" LSD that exists on the 335i? My driving is 25-30% canyons, 5% track, and the rest is around-town stuff.

Also, is there a chance that BMW would look to modify the 335i in upcoming models to address this issue?

I am new to the world of the 335i and interested in some minor modifications on my ride. Is there a reliable aftermarket mechanical, helical LSD that exists to replace the "virtual" LSD that exists on the 335i? My driving is 25-30% canyons, 5% track, and the rest is around-town stuff.

Also, is there a chance that BMW would look to modify the 335i in upcoming models to address this issue?

IT's called the M3...comes with a real LSD.

There are a few options, which include Quaife

OK. This is great but I do have 1 last question: Does the 335's electronic version of limited slip work when all traction control is turned off?

I am new to the world of the 335i and interested in some minor modifications on my ride. Is there a reliable aftermarket mechanical, helical LSD that exists to replace the "virtual" LSD that exists on the 335i? My driving is 25-30% canyons, 5% track, and the rest is around-town stuff.

Also, is there a chance that BMW would look to modify the 335i in upcoming models to address this issue?

Hello "speeddoc74":

But then again, will the differential, transmission, and rear axle handle the power? In one of the early 80 Cameros that we built, even using the 9 bolt rear end, we could not keep things together until we ran it "open". It took a bit more effort to launch, but with the "posi" he was breaking ring gears and U-joints with a measly 600 Hp supercharged small block. Once we put in an "open" differential, no more problems.

OK. This is great but I do have 1 last question: Does the 335's electronic version of limited slip work when all traction control is turned off?
If you push and hold the DTC button for a few seconds, it will be of. I believe it is still on if you just activate DTC (just press the button).

Hello "speeddoc74":

But then again, will the differential, transmission, and rear axle handle the power? In one of the early 80 Cameros that we built, even using the 9 bolt rear end, we could not keep things together until we ran it "open". It took a bit more effort to launch, but with the "posi" he was breaking ring gears and U-joints with a measly 600 Hp supercharged small block. Once we put in an "open" differential, no more problems.

Drag racing is known to be axle breakers. You're asking about the quality of a product. I see your point is that there may be axle issues, but those should be built to handle the power. It's not increasing power, it's using the same power more efficiently. The M3 will have much more power on a true LSD.

I'll use my 350Z as an example as I am much more familiar with what it can take. Even with twice as much HP as stock (we had cars at over 500whp) the axles weren't an issue until they were on the strip with DRs. I'm assuming BMW can build things as strong as Nissan. Heck I went from 240whp to 340whp and it never made a difference.

Drag racing is known to be axle breakers. You're asking about the quality of a product. I see your point is that there may be axle issues, but those should be built to handle the power. It's not increasing power, it's using the same power more efficiently. The M3 will have much more power on a true LSD.

I'll use my 350Z as an example as I am much more familiar with what it can take. Even with twice as much HP as stock (we had cars at over 500whp) the axles weren't an issue until they were on the strip with DRs. I'm assuming BMW can build things as strong as Nissan. Heck I went from 240whp to 340whp and it never made a difference.

Hello "Beer Goggles":

You picked up on part of my point. If someone adds an LSD to a 335i will the rest of the power train handle it? The Camaro could not. If we boost a 335i and then add an LSD, will we break an axle? Are there differences between the 328 sedan and the 335 sedan drive train. I cited one example of where a vehicle did better with an open differential because things did not break.

You are correct only if wish to refer to the BMW implementation as a limited slip process. The actual, real, physical 'differential' (the 'D' in LSD) is an open one. Now, the type of LSD can vary - it can be clutch based or helical based, but the means to limit slip (the 'LS' in LSD) is purely mechanical.

To imply that the 335i has an LSD only serves to confuse. It simulates a true LSD, but it does not contain one.

-Dave
I get what you guys are saying, I just wish you were saying it right. When you refer to LSD, you mean one particular means of providing a limited slip differential between the tires on an axle, mechanical torque sensitive. You're omitting clutch pack, viscous, electronic, and other speed sensitive forms. You're speaking of a particular device, not the act of providing a limited difference in slip.

No it's not. Limited Slip Differentials refer to mechanical means to distribute power to the proper wheel. REAL LSDs has clutches or viscous packs that mechanically alter the force being distributed via the differential.This is where you're wrong. Viscous and clutch pack(note: there's a big difference between clutch and clutch pack) are both speed sensitive and NOT considered mechanical. It isn't any more mechanical than applying a brake to one tire, and in fact is the same thing(although as Beer Goggles stated the electronic system is more reactive whereas viscous fluids offer more real-time action). What do you think that viscous fluid does, exactly? It provides drag as speed increases, it brakes the rapidly rotating side. Re-read your stuff... AND comprehend ;-)

I get the point everyone's trying to make, they want a torque sensitive LSD in particular. I'd just have an easier time letting this go if some of you guys at least sounded like you knew what you were talking about ;-) I just hope that if you end up buying an aftermarket LSD you know exactly which kind you're getting...

It isn't any more mechanical than applying a brake to one tire, and in fact is the same thing(although as Beer Goggles stated the electronic system is more reactive whereas viscous fluids offer more real-time action).
I believe viscous LSD is also somewhat reactive, not as realtime as a torsen or clutch based.

Hello "Beer Goggles":

You picked up on part of my point. If someone adds an LSD to a 335i will the rest of the power train handle it? The Camaro could not. If we boost a 335i and then add an LSD, will we break an axle? Are there differences between the 328 sedan and the 335 sedan drive train. I cited one example of where a vehicle did better with an open differential because things did not break.

Obviously you had weak points in the drivetrain which were cured by reducing power/traction to the ground with an open diff. I'm sure that 600hp and probably the same amount of torque is much more hard to deal with than half that :)


If you have a 600hp 335i odds are you should have upgrade the driveline to work, I'm assuming the M3 shares parts, and that they test to have parts that don't fail under load.

In an open diff, if the wheel is spinning it's it's twice the speed of the one not moving, which would mean it can take twice the load (considering worst case is that the spinning wheel becomes the traction wheel)...an LSD will reduce wheel spin to always be equal.

But somebody find out. switch it, boost it, break it. Report.

I believe viscous LSD is also somewhat reactive, not as realtime as a torsen or clutch based.

Um, torsen and clutch based diffs ARE Limited Slip Diffs. :rolleyes

Um, torsen and clutch based diffs ARE Limited Slip Diffs. :rolleyes
Doh, I know, you guys should learn to read carefully before jumping the gun. These are all types of LSD, but the viscous LSD is reactive in nature v.s. the others.

I have some questions about the Electronic LSD and the DSC/DTC.
Hi, jbass. Sorry it took so long to get back to you. Unfortunately, I don't know enough about the 335i electronics to answer many of your questions yet. :(

Does anyone know how the electronic LSD works and when it works in a 335? I've been told that it only works when the DTC is on and when traction control is off it doesn't work at all. The same person told me that when it is working it tries to put power to the lightest wheel.

Is it true that the DTC uses only brake brakes for traction control and not the power? I understand that the DTC reverts to DSC if the car experiences more then 0.4 Gs. True?
I cannot vouch for these details yet, sorry. :(

I do know that in my last car, the traction control switch that turned off the traction control didn't work. Well, let me rephrase that. It would drop a voltage signal to the ECU to tell it traction control should be off, but the ECU still used some engine management functions to retard power going to the rear wheels.

However, pulling one of the fuses for that ECU completely disabled the traction control.

Unfortunately, it also disabled the speed limiter. :lol (Too bad, huh? ;))

If I want the best performance from my stock 335 on the track what should I do with traction control considering all of the above: DTC on or traction control completely off?

Thanks for your time.
What type of "track" are you referring to?

For example, here in Florida we have the option to take our cars on the oval at Daytona (if you're willing to pay enough and wait for the right time). However, I would strongly recommend against it for a street car: most street vehicles do not have strong enough water and/or oil pumps to prevent engine damage from sustained runs on 30* or more of banking. :(

If you're thinking more along the lines of Sebring (a flat track), I can't give a definite answer until I learn more about the ECU electronics. :(

In general, if the traction control is about to kick in, you're driving too hard. :) One of the first rules in autocrossing is to keep the power to the drive wheels such that they never slip. If they do, it was too much power. :) Of course, easier said than done. The best (only?) way to learn when that tire slippage is about to occur is seat time -- practice. (And since track conditions change constantly during an event, that has to be factored in as well.)

I'm hoping that hanging around forums like this one, as well as reading every brochure and factoid that I can find on the 335i, I might be able to glean some of the information you're looking for. My experience has been that the shop manuals can sometimes help with this, since they provide theory of operation notes for most major subsystems in the car, but details like pulling the fuse are only likely to be learned from a tuner or other performance shop. (I found out from a fellow autocrosser who found out from a performance shop in Orlando.)

Sorry I don't have a better answer. :( And it particularly bums me out that sor recommended me (thanks, sor!) and then I fell short. :( I'll try to make it up to you down the road...

I wasn't sure if you'd now the technical details, but I got the impression that you had enough track time in to give a real-world take as to which settings seem to do what or which are best. Sorry!

azhrei (http://forums.bimmerforums.com/forum/member.php?u=100868) and sor (http://forums.bimmerforums.com/forum/member.php?u=129852),

Thanks for your consideration. I am blown away by the amount of concern you have in giving me the right answer. Amazing.

I'm referring to Infineon (Sears Point) as the track. I will also do some time at Thunderhill.

I have been getting great instruction and have been making good progress. I've been told it's time to turn the traction control completely off but when I did the effect didn't seem that favorable. I wasn't worried about the car letting go on the edge so it isn't a case where I feel more comfortable due to traction control it's an issue of what is the best setting if I really wanna feel the car. I'm really trying hard to become a better track driver.

My experience gives me the funny feeling that the open dif in my car works better when the electronics are on. This is why I was wondering about the how and when the eLSD in the 335 works.

Thanks again.

jbass,

It sounds like you are certainly on the right road.

If you get the opportunity, have your instructor drive your car for a few laps with and without the various electronics. (Most long-term race training would include some kind of periodic ride-along where the student sits in the passenger seat as a way to gauge what the limits of the car are.)

If you don't think the car feels as good with the electronics off, don't turn them off. Driving a race car is tricky stuff. Some people will laugh when you tell them, "it didn't feel right", and others will nod their head and smile knowingly. Don't concern yourself about either group and simply drive your car to the best of your (and its) ability. Part of the trick is knowing how far you can push it and that's why the ride-along can be so useful.

Both of the tracks you mentioned are flat tracks, IIRC. That means the most cost-effective upgrades you can do to the car will be tires (duh!) and suspension. I don't know what you're doing for tires now, but I used to hang around at Sebring when the race teams were practicing or qualifying. When a team finishes, they will take the qualifying tires off the car (after only 3-4 laps) and deliver them to the tire manufacturer's semitrailer for recycling/disposal. You need to be near that truck so that you can chat up the driver (usually it's just one guy). He might be busy mounting or unmounting tires, so don't hassle him too much.

Let him know that you'd be interested in any 18" tires that look like they're still in good shape. I've been able to slip $50 to one of these guys and drive away with a set of virtually brand-new track tires! My Supra's wheels were 17x10.5 in the rear and 17x9.5 in the front, so putting 335's on the rear was perhaps a little too wide. Except that race tires have very stiff sidewalls and these would only be used on track days, and my springs were very stiff, so I did it anyway. :) (PS: the truck guy is not supposed to do this, so be sure to be courteous and generous with him. :))

Good luck, jbass. And let us know how it turns out! I for one am truly interested. :)

Azhrel

In your sig talking about your 335 in the shop for the "stiff brake" problem, what are you referring to?

Both of the tracks you mentioned are flat tracks, IIRC. That means the most cost-effective upgrades you can do to the car will be tires (duh!) and suspension. I don't know what you're doing for tires now, but I used to hang around at Sebring when the race teams were practicing or qualifying. When a team finishes, they will take the qualifying tires off the car (after only 3-4 laps) and deliver them to the tire manufacturer's semitrailer for recycling/disposal. You need to be near that truck so that you can chat up the driver (usually it's just one guy). He might be busy mounting or unmounting tires, so don't hassle him too much.

Let him know that you'd be interested in any 18" tires that look like they're still in good shape. I've been able to slip $50 to one of these guys and drive away with a set of virtually brand-new track tires! My Supra's wheels were 17x10.5 in the rear and 17x9.5 in the front, so putting 335's on the rear was perhaps a little too wide. Except that race tires have very stiff sidewalls and these would only be used on track days, and my springs were very stiff, so I did it anyway. :) (PS: the truck guy is not supposed to do this, so be sure to be courteous and generous with him. :))

Good luck, jbass. And let us know how it turns out! I for one am truly interested. :)

You recalled wrong. Both of those tracks are the biggest elevation changers in California outside of Laguna Seca. THill even has 2 separate giant hills with one that looks very much like Laguna Seca's famed "cork screw". Turn 2 at Sears is notorious for the elevation change.

As for the tire advice, I'll have to respectfully disagree. If your goal is to make your car go faster, you don't need to go to the track to learn that. If your goal is to make your car go faster by making yourself go faster, going to race tires or r-comps is about the last thing that'll make you fast. I've had several students come to the track on r-comps, and the first thing I ask is that if they have street tires with them, put the street tires back on. I've seen this time and time again. People with R-comps always go fast in the first two sessions of the day, but they stop learning quick, because the r-comps covers up all their mistakes, and by the end of the day the guys on street tires catches up and passes them. I would say stay off the r-comps as long as you can.

Regarding leaving the electronic nannies on or off...Leave it on for as long as you can. If and when you can drive the car without any of the electronics intervening to save your life, then you can turn it off. You'll find that if you can drive the ideal lap, be on-line and be smooth, the electronics will never cut-in to interfere. If you can string together an entire session without any of the electronics cutting in to interfere, then talk to your instructor about turning it off.

The ONLY two places where the open diff may be a big disadvantage at Sears Point is turn 7 and turn 11. The slow speed tight 180 degree turns. And even with those two turns if you can learn how to effectively minimize the amount of time your inside tires are slipping, you can minimize the in-ability to lay down power to the inside tire. Try double-apexing turn 7, turn-in, clip the inside apex, lift-throttle-steer mid-turn, ease-in the throttle and unwind out. The less time you spend with the outside tire completely loaded, the more time the engine is laying down power to the wheels. For turn 11, try it like you're driving a very heavy car, late apex it and spend as much time unwinding as you possibly can.

But leave the electronic nannies on.

azheri and Hack,

Thank you for the response.

Hack, I feel like I've had you for an instructor before because of how you laid it out. It makes total sense to drive perfectly enough for the electronics not to come on.

I feel the electronics a tiny bit in turn 11. Turn 7 is a good one for me and funny enough I do feel them now and again in turn 2. I will adjdjust next time I'm there.

I can't justify r-comps considering how much I need to learn. As of right now my car is far more capable than I even with the Bridgestone run flats on there.

Thanks again to all of you.

Hack, I feel like I've had you for an instructor before because of how you laid it out. It makes total sense to drive perfectly enough for the electronics not to come on.

If you're going to the BMW CCA Golden Gate Chapter school at Thunderhill in August, there might be a chance this may come true. :D

You recalled wrong. Both of those tracks are the biggest elevation changers in California outside of Laguna Seca.
Figures. That's what I get for posting off the cuff and not checking the details. :)

As for the tire advice, I'll have to respectfully disagree. If your goal is to make your car go faster, you don't need to go to the track to learn that.
Yep. I think I said that in an earlier post (but I'm too lazy to go find it!).

But he had indicated that he'd already had a couple of classes, so I figured he had already been told about the basics -- the same things you reiterate in your posting -- and would be interested in "the next step."

I would say stay off the r-comps as long as you can. [...] Leave it on for as long as you can.
Also agreed. And I think I said that, too. (Or maybe not. It's 3:30am in the morning and I'm going to bed and I'm not going to scan previous posts!)

Ciao.

I have some questions about the Electronic LSD and the DSC/DTC.

Does anyone know how the electronic LSD works and when it works in a 335? I've been told that it only works when the DTC is on and when traction control is off it doesn't work at all. The same person told me that when it is working it tries to put power to the lightest wheel.

Is it true that the DTC uses only brake brakes for traction control and not the power? I understand that the DTC reverts to DSC if the car experiences more then 0.4 Gs. True?

If I want the best performance from my stock 335 on the track what should I do with traction control considering all of the above: DTC on or traction control completely off?

Thanks for your time.

I believe it operates like an electronic LSD. When one wheel spins the system brakes that wheel, transferring power over to the other wheel. It's a neat system, actually, and I've had good luck with it. I still use drag radials at the drag strip though.. :)