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Old 02-03-2003, 07:15 AM
webguy330i webguy330i is offline
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DSC and an LSD

So I was thinking today, and perhaps once again I will be restating what has already been said on the board... but I was thinking that an LSD would adversely affect the stability management systems in our cars.

Let me say again that I realize I might be stating the obvious.

Anyhow, I came to this conclusion because I was driving today and one of my rear wheels passed over some slush/ice whilst I was "aggressively" accelerating. The car didn't even flinch, save the slight throttle decrease causing me to lunge forward in my seat for about a 1/2 a second. I immediately attributed this to the open differential, and since both rear wheels turn independently of one another, the stability system was able to take away some throttle and probably brake that one rear wheel as it slipped.

I figured that if I had a locking (heh, like I'd use that on the street), VC or Torsen differential, the stability system would be unable to control just one of the two rear wheels, and therefore both rear wheels may have spun when I hit the ice patch. On the other hand, the traction of the one tire NOT in the ice/slush may have been enough to keep the tire IN the ice/slush from spinning.

This all came about because I was driving my g/f's IS300 after she had repeatedly stated that the car "sucked in the snow" and I discovered that it does indeed suck. Her car has the Torsen LSD that came with it, and snow tires for the winter (LM-22s). I was able to get the rear end out completely and back around while the traction control software attempted to interfere, failing miserably. I haven't tried anything like this with an IS300 sans the LSD, but I imagine it's much easier for the stability system to get the car under control. Also it's apparent that the IS300's traction system doesn't steal from the throttle like our cars do, until you manually put the car in "snow" mode.

Anyhow, just thought I'd share... I look at this as a sort-of good thing, not having an LSD, but it's really only applicable in the winter. I'd trade winter traction for spring/summer/fall dry-pavement traction and fun anyday.
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Last edited by webguy330i; 02-03-2003 at 07:19 AM.
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  #2  
Old 02-03-2003, 07:21 AM
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seems to work okay together in my car
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Old 02-03-2003, 07:22 AM
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Hmm...The M cars seem to do ok with LSD and DSC...

Though, I have been in one that spun with DSC on while on a skidpad, not that the stability system can prevent everything....
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Old 02-03-2003, 07:28 AM
webguy330i webguy330i is offline
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atyclb, isn't the M-diff a computer-controlled hydraulic system? It's not a mechanical diff like a Torsen right? I'm wondering if the stability management system is able to intervene before the LSD is "enabled" so-to-speak, thus allowing an open-diff type scenario.
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Old 02-03-2003, 07:30 AM
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Old 02-03-2003, 07:34 AM
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Quote:
Originally posted by webguy330i
atyclb, isn't the M-diff a computer-controlled hydraulic system? It's not a mechanical diff like a Torsen right? I'm wondering if the stability management system is able to intervene before the LSD is "enabled" so-to-speak, thus allowing an open-diff type scenario.
AFAIK, the M3 differential is not computer controlled...

Anyway, the M5, and all Z3s do not have the M-Lock and do ok...
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Old 02-03-2003, 07:51 AM
webguy330i webguy330i is offline
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Quote:
Originally posted by nate328Ci
AFAIK, the M3 differential is not computer controlled...

Anyway, the M5, and all Z3s do not have the M-Lock and do ok...
I believe you're right, just read a little article on the "M variable differential lock". It's a clutch-type LSD also, but is able to overcome the "one-wheel-zero traction * torque bias = 0" problem that is inherent to the Torsen LSD.

Oh well there goes my theory. I think the IS300 traction issues are related to the stability software not controlling the throttle outside of snow mode. Or so it seems...
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