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  #1  
Old 02-17-2005, 08:03 AM
EZ EZ is offline
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Question Open diff vs. BMW pseudo-LSD

Somebody has stated in another thread that an open differential is better than the BMW pseudu-LSD functionality (achieved with one punch to the DSC button in E46 -- brakes applied to the free-spinning wheel). I have a problem with this assertion, and I posted the following question, but the discussion died down. Therefore, I am trying to revitalize it here, because this issue is a concern to me.

Here is my understanding. Suppose, you are exiting a corner and applying throttle. The inner wheels lift and loose surface traction. Because the throttle is open, the rear inner wheel start spinning as mad, cutting off all the power from the one with traction. I felt this a number of times, when the car looses power at the exit (with the psuedo-LSD disabled via a 5 s hold to the DSC button). The best what one can do in this situation is to lift gently and regain traction smoothly. The worst -- to gain traction abruptly, upset the car and possibly get into a spin. The latter has happened to me once at an auto-x.

If the psuedo-LSD kicks in, it slows down the wheel that isn't working anyway, and in doing that, applies power to the wheel that is doing its job. Why is this worth than an open differential?
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  #2  
Old 02-17-2005, 08:11 AM
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Nick325xiT 5spd Nick325xiT 5spd is offline
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ADB isn't that much different from traction control. It ****s with my chi, and makes the car behave unpredictably.

I will be installing an LSD in my 323 ASAP, but I would MUCH rather deal with extra wheel spin than have a computer interfering.

Now, it is possible for ADB to function well. The problem, IMHO, is that it's been programmed for the street and is far too invasive.
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Old 02-17-2005, 08:26 AM
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The open diff is better because you can manage throttle (and wheel spin) directly and anticipate traction. ADB can't tell the difference between an accidental spins and intented power slides, so it just applies brakes for everything. ADB thinks that any wheel spin is bad, and with autocross a little wheel spin is usually ok. ADB senses this wheel spin and over dampens it, causing you to lose more power than you need and slows you way down.
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Old 02-18-2005, 08:18 AM
EZ EZ is offline
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Guys, thanks a lot for your comments.
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Old 02-18-2005, 08:42 AM
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Quote:
Originally Posted by Nick325xiT 5spd
ADB isn't that much different from traction control. It ****s with my chi
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Old 02-18-2005, 09:55 AM
Andre Yew Andre Yew is offline
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Differential braking, of which the BWM DSC system is a simplified version, can be made to work very well, to the extent that it's banned in F1. In addition to helping you put power down in exits, it can be used as a steering system as well.

--Andre
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Old 02-18-2005, 10:04 AM
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Quote:
Originally Posted by Andre Yew
Differential braking, of which the BWM DSC system is a simplified version, can be made to work very well, to the extent that it's banned in F1. In addition to helping you put power down in exits, it can be used as a steering system as well.

--Andre
Yes, but the point is that the BMW version doesn't. Anything else is irrelevant.
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Old 02-18-2005, 10:17 AM
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Quote:
Originally Posted by Nick325xiT 5spd
Yes, but the point is that the BMW version doesn't. Anything else is irrelevant.
I agree that the BMW DSC in the default mode is highly intrusive, and that it is not a good system. You clearly don't want to have it "on" on a track.

I am less certain about the one-step-disabled DSC, which has a psuedo-LSD functionality. Personally, I haven't found it excessively intrusive. This however, may come with more experience. I guess, I should just experiment more with completely disabled DSC and compare it to the one-step disabled one.
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Old 02-18-2005, 10:19 AM
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Quote:
Originally Posted by EZ
I agree that the BMW DSC in the default mode is highly intrusive, and that it is not a good system. You clearly don't want to have it "on" on a track.

I am less certain about the one-step-disabled DSC, which has a psuedo-LSD functionality. Personally, I haven't found it excessively intrusive. This however, may come with more experience. I guess, I should just experiment more with completely disabled DSC and compare it to the one-step disabled one.
I find it extraordinarily intrusive. The fact that you spun the car trying to cure wheel spin says a lot more about your driving than about ADB.
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  #10  
Old 02-18-2005, 10:28 AM
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Quote:
Originally Posted by Nick325xiT 5spd
I find it extraordinarily intrusive. The fact that you spun the car trying to cure wheel spin says a lot more about your driving than about ADB.
I am not pretending to be Mike Schumacher
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  #11  
Old 02-18-2005, 03:53 PM
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The Z4 3.0 Sport with Hoosier Wet rain radials would make mincemeat out of the competition in the rain when set in the intermediate DTC mode:

Quote:
A briefer push, however, selects the new Dynamic Traction Control (DTC) function.

The normal traction-control function not only applies the brakes of individual wheels as they start to slip, but also reduces engine power. This keeps the vehicle very stable, but under certain conditions (such as climbing a snow-covered hill) can leave little power to move forward. At low speeds and in gentle cornering maneuvers, DTC allows more wheel spin by de-activating engine intervention. As speed and/or cornering vigor increases, DTC progressively restores engine intervention. To the driver, DTC means -

Enhanced traction under low-friction conditions (sand, gravel, deep or packed snow).
Allowing greater use of the driver's skill at low speeds under these low-friction conditions.
Maintenance of full DSC stability benefits under higher-speed, more vigorous driving conditions.
contrary to the idea that the car is doing all the work and the driver is just along for the ride, the driver has to be both smooth and aggressive to get the most out of it and it takes a lot of discipline to do so. I even won an SCCA Pro Solo event (Atlanta/2004) in the rain on the original runflat street tires against people running racing rain tires
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