LSD

m3dude · 11-12-2014, 02:12 PM

Hey Guys,

didn't find any threads mentioning this so I'll ask.

When coming out of low speed corners I am having trouble consistently engaging the LSD when I am coming hard out of a tight corner. I find that half the time it locks up 100% to let the tail slip out, and half the time it prevents wheel spin. I find that when I am in MDM it prevents the back end from coming out much better. But I also find MDM a bit too intrusive for faster corners. SO, does anyone have any advice on throttle technique to make sure the LSD doesn't lock up 100% when coming hard out of a corner?

m3ray · 11-12-2014, 02:42 PM

http://www.m3post.com/forums/showthread.php?t=1055255

http://www.m3post.com/forums/showthread.php?t=788992

A lot of LSD's claim to lock up 100%, but don't.

FTS · 11-12-2014, 02:53 PM

Wouldn't it make sense that if the diff was in 100% lock under power out of a corner that the car would go into severe understeer, instead of pushing the tail out?

driftflo · 11-12-2014, 02:57 PM

Quote:

Originally Posted by m3dude

When coming out of low speed corners I am having trouble consistently engaging the LSD when I am coming hard out of a tight corner. I find that half the time it locks up 100% to let the tail slip out, and half the time it prevents wheel spin. I find that when I am in MDM it prevents the back end from coming out much better. But I also find MDM a bit too intrusive for faster corners. SO, does anyone have any advice on throttle technique to make sure the LSD doesn't lock up 100% when coming hard out of a corner?

the stock lsd (GKN viscolok) needs one wheel to spin significantly faster than the other to generate its lockup. think of an old turbo...

so this unit is slow-performing and hardly predictable. slow and difficult to drive on the limit. you need to switch to a proper clutch-type lsd (as bmw does in all their racecars like m3 gt4).

links to good sources have already been posted above.

driftflo · 11-12-2014, 03:03 PM

Quote:

Originally Posted by FTS

Wouldn't it make sense that if the diff was in 100% lock under power out of a corner that the car would go into severe understeer, instead of pushing the tail out?

depends... in general (more) lockup means (more) understeer.
so a proper high locking clutch-type lsd equiped racecar needs this to be sorted out via suspension- and stabiliser-setup.

but in certain circumstances when two spinning wheels loose traction while cornering they move sideways. you normally hit the gas AFTER the apex. and after the apex the steering goes back to straight/neutral. so the front wheels will have no problem to get enough traction. this is the reason for power oversteering (and not understeering) on corner exit!

with an open diff (what the viscolok is shortly after you apply throttle) only one wheel spins and the outer wheel still has traction so the car keeps in line but doesnt push forward as it could. when the viscolok turns from open to locking, the outer wheel could also spin if you still apply enough throttle.

knolow · 11-12-2014, 09:32 PM

Quote:

Originally Posted by FTS

Wouldn't it make sense that if the diff was in 100% lock under power out of a corner that the car would go into severe understeer, instead of pushing the tail out?

Mannnnnn I thought the same. And would have blamed the issue on throttle input as in to heavy of a foot and not gradual input.

Quote:

Originally Posted by driftflo

depends... in general (more) lockup means (more) understeer.
so a proper high locking clutch-type lsd equiped racecar needs this to be sorted out via suspension- and stabiliser-setup.

but in certain circumstances when two spinning wheels loose traction while cornering they move sideways. you normally hit the gas AFTER the apex. and after the apex the steering goes back to straight/neutral. so the front wheels will have no problem to get enough traction. this is the reason for power oversteering (and not understeering) on corner exit!

with an open diff (what the viscolok is shortly after you apply throttle) only one wheel spins and the outer wheel still has traction so the car keeps in line but doesnt push forward as it could. when the viscolok turns from open to locking, the outer wheel could also spin if you still apply enough throttle.

Driftflo you need to write a book on this topic. I'd be the first to buy a copy.

driftflo · 11-13-2014, 02:32 AM

i wrote a website on that topic. but it is in german only so far.
www.limitedslip.de

when i have some leisure time i am thinking of translating it but as i am no native speaker this will be a tough job for me.

maybe i simply start with the translation and you guys help to correct it then... ;-)

LiM3y · 11-13-2014, 08:25 AM

This sounds like throttle control rather than LSD issues...the comment that MDM stops this reinforces this notion as it controls throttle input and individual wheel braking. Maybe spend $60 on some lighter shoes before $1000's on a race LSD?

m3dude · 11-13-2014, 09:38 PM

Yup. Tried less aggressive throttle application today and the LSD worked fine. (yes you are right m3ray I flipped the terminology). Wish it were a bit more aggressive, but then there would be less shenanigans so its a compromise.

italyix · 11-13-2014, 10:25 PM

Quote:

Originally Posted by driftflo

i wrote a website on that topic. but it is in german only so far.
www.limitedslip.de

when i have some leisure time i am thinking of translating it but as i am no native speaker this will be a tough job for me.

maybe i simply start with the translation and you guys help to correct it then... ;-)

Google translate works wonders. I'm able to read ur website, just have google translate it.

CSBM5 · 11-14-2014, 09:56 AM

Quote:

Originally Posted by italyix

Google translate works wonders. I'm able to read ur website, just have google translate it.

...and the link: http://translate.google.com/translat...e/&prev=search

FTS · 11-14-2014, 11:51 AM

Quote:

Originally Posted by driftflo

i wrote a website on that topic. but it is in german only so far.
www.limitedslip.de

when i have some leisure time i am thinking of translating it but as i am no native speaker this will be a tough job for me.

maybe i simply start with the translation and you guys help to correct it then... ;-)

Very good information, and thank you for answering my question. I understand your point, but I am not certain the situation you describe is what is happening with OPs experience, not enough info from OP on that.

That being said, I think most of us have very little knowledge and understanding of differentials beyond the basic concepts, and I don't know if we are able to feel, as drivers, much of what is going on with the diff, particularly with the latest electronics diffs coupled with the DSC and ABS systems. Maybe I am the only one in this situation.

I'll keep reading the info at your site, and I hope I can get better at feeling what the diff is doing, that is my weakest point at this time; I don't think the new M diff in the F8x will make it any easier for me

Thank you once again.

11-12-2014, 02:12 PM	#1
m3dude Private 17 Rep 88 Posts Drives: 09 DCT e92 m3, Subaru Legacy Join Date: Mar 2013 Location: cincinnati/ann arbor iTrader: (0)	LSD Hey Guys, didn't find any threads mentioning this so I'll ask. When coming out of low speed corners I am having trouble consistently engaging the LSD when I am coming hard out of a tight corner. I find that half the time it locks up 100% to let the tail slip out, and half the time it prevents wheel spin. I find that when I am in MDM it prevents the back end from coming out much better. But I also find MDM a bit too intrusive for faster corners. SO, does anyone have any advice on throttle technique to make sure the LSD doesn't lock up 100% when coming hard out of a corner?
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11-12-2014, 02:42 PM	#2
m3ray Banned 106 Rep 701 Posts Drives: '09 e92 M3 Join Date: Jun 2014 Location: New York City iTrader: (0)	http://www.m3post.com/forums/showthread.php?t=1055255 http://www.m3post.com/forums/showthread.php?t=788992 A lot of LSD's claim to lock up 100%, but don't.
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11-12-2014, 02:53 PM	#3
FTS Enjoying driving 394 Rep 1,169 Posts Drives: 645 Join Date: May 2009 Location: MD iTrader: (0)	Wouldn't it make sense that if the diff was in 100% lock under power out of a corner that the car would go into severe understeer, instead of pushing the tail out?
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11-13-2014, 02:32 AM	#7
driftflo Second Lieutenant 543 Rep 299 Posts Drives: M3T G81, M2 F87, M3 E92, 911 G Join Date: May 2012 Location: Europe iTrader: (0) Garage List 2025 BMW M3 G81 [9.50] 2018 BMW M2 F87 [0.00] 2012 BMW M3 E92 [0.00]	i wrote a website on that topic. but it is in german only so far. www.limitedslip.de when i have some leisure time i am thinking of translating it but as i am no native speaker this will be a tough job for me. maybe i simply start with the translation and you guys help to correct it then... ;-)
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11-13-2014, 08:25 AM	#8
LiM3y Major 94 Rep 1,339 Posts Drives: 2008 E90 M3 Join Date: Jun 2009 Location: CT iTrader: (5)	This sounds like throttle control rather than LSD issues...the comment that MDM stops this reinforces this notion as it controls throttle input and individual wheel braking. Maybe spend $60 on some lighter shoes before $1000's on a race LSD? __________________
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11-13-2014, 09:38 PM	#9
m3dude Private 17 Rep 88 Posts Drives: 09 DCT e92 m3, Subaru Legacy Join Date: Mar 2013 Location: cincinnati/ann arbor iTrader: (0)	Yup. Tried less aggressive throttle application today and the LSD worked fine. (yes you are right m3ray I flipped the terminology). Wish it were a bit more aggressive, but then there would be less shenanigans so its a compromise. Last edited by m3dude; 11-13-2014 at 10:03 PM..
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