# Having no LSD really, really suck. (Buttonwillow 2-day with SpeedVentures)



## Nick325xiT 5spd (Dec 24, 2001)

WILLIA///M said:


> Nice driving in the race vid. :thumbup: Didn't look like you were going to get the yellow E36 at the end but you did. Thanks for posting those.


 That guy's car was completely gutted out and had some engine work done. It was just painful watching him disappear on the straights.


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## Mr Paddle.Shift (Dec 19, 2001)

TeamM3 said:


> the opening post sounded more like you're getting your butt kicked, not spinning an inside drive tire :dunno: an LSD won't fix that


Or his LSDs + 4WD have the edge over my open-diff. I was there with him on the track all the way. He brakes at places that shouldn't even be slowed down to. I am confident my skills are better than him.



TeamM3 said:


> I never had wheel spin issues with my non-LSD Z4 3.0 :dunno:


Not driving hard enough!



TeamM3 said:


> I also fail to see how you "saw" the Evo8's LSD working, more likely just AWD traction and a powerful turbo motor operating in the boost powerband :dunno:


I use "saw" metaphorically. For instance, "He vomitted so much after the party, I swear I _saw_ his internal organs spilling out!".


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## Mr Paddle.Shift (Dec 19, 2001)

Nick325xiT 5spd said:


> I retired the M3 from the track in favor of the 323.


Ah...probably missed your post about that.

Btw, from the video, it appears that this is an open passing event. The white E36 was attempting to make a pass on the yellow E36 earlier on, but backed off a little befor the turn. Did I interpret it wrong?


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## Nick325xiT 5spd (Dec 24, 2001)

Mr Paddle.Shift said:


> Or his LSDs + 4WD have the edge over my open-diff. I was there with him on the track all the way. He brakes at places that shouldn't even be slowed down to. I am confident my skills are better than him.
> 
> Not driving hard enough!
> 
> I use "saw" metaphorically. For instance, "He vomitted so much after the party, I swear I _saw_ his internal organs spilling out!".


 Vince, why couldn't he just have more power than you? Just because you have an open diff does not necessarily mean that you are burning the inside tire.

And I can pretty much guarantee that Mark's a faster driver than you.


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## Nick325xiT 5spd (Dec 24, 2001)

Mr Paddle.Shift said:


> Ah...probably missed your post about that.
> 
> Btw, from the video, it appears that this is an open passing event. The white E36 was attempting to make a pass on the yellow E36 earlier on, but backed off a little befor the turn. Did I interpret it wrong?


 Yes, pass anywhere. It's the BMWCCA Club Racing School. Download the second video--It's even better.


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## Mr Paddle.Shift (Dec 19, 2001)

Appreciate the insight. I am off to another event at the same location next week. I will post my findings.

So regarding the airborne feeling, to be able to see the ground on my side, then it's almost a 30~45deg incline?  Even 1mm above the ground is considered airborne, no? But I guess it's not like we can feel that small of a change. What I am interested seems to lie in _how high for how long being in an airbone state before one has to correct significantly_, which of course is directly correlated to the suspension setup, the speed over the bump, the traction and the properties of the tire rubber at that moment.

I think I ponder on this too much. Just that it's exciting to understand the car's behavior from a physics POV.



Pinecone said:


> Nope, only one wheel has to get light to find the problems with open diffs. And once one gets light enough to start spinning, you have no forward drive. Open diff will put ALL the power on the wheel with less traction.
> 
> You can still get power oversteer with an open diff. But, if the body roll lightens the inside wheel and it starts to spin, a spining wheel has 30% less traction than a rolling wheel so you lose virtually all the cornering on that spinning wheel, leading to oversteer in some cases.
> 
> I doubt you got the side of the car airborne, probably just got it light. It just felt like it was airbrone. Unless your car is sprung very stiffly or over swayed, by the time the side gets airborne you are looking out your side window at the ground.


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## Mr Paddle.Shift (Dec 19, 2001)

I was just messing around with Mark. :eeps: 

Yes that Evo has 4WD, LSDs and probably engine modifications. That's more comforting to know. :angel: I got a feeling this bloke will be at the next event. We will meet again!



Nick325xiT 5spd said:


> Vince, why couldn't he just have more power than you? Just because you have an open diff does not necessarily mean that you are burning the inside tire.
> 
> And I can pretty much guarantee that Mark's a faster driver than you.


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## CSBM5 (Mar 10, 2004)

Re open diffs...it's been many years since I've tracked a car with an open diff, but you'll find that if you take out some rear roll stiffness (maybe go to a higher rate rear spring to compensate, etc.), you get better inside wheel traction off the turns. Also, if you have the room, opening up the steering lock just a bit as you ease off the throttle can help you regain traction and get back into the throttle on track out (i.e. turn 2 at VIR).

Once you add a LSD to the car, you will likely find that you need to retune the suspension to take out understeer which is now apparent with the rear end hooked up better.

Chuck


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## Pinecone (Apr 3, 2002)

TeamM3 said:


> the opening post sounded more like you're getting your butt kicked, not spinning an inside drive tire :dunno: an LSD won't fix that
> 
> I never had wheel spin issues with my non-LSD Z4 3.0 :dunno:
> 
> I also fail to see how you "saw" the Evo8's LSD working, more likely just AWD traction and a powerful turbo motor operating in the boost powerband :dunno:


Or someone with superior corner speed along with teh compression effect.


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## Pinecone (Apr 3, 2002)

Mr Paddle.Shift said:


> Appreciate the insight. I am off to another event at the same location next week. I will post my findings.
> 
> So regarding the airborne feeling, to be able to see the ground on my side, then it's almost a 30~45deg incline?  Even 1mm above the ground is considered airborne, no? But I guess it's not like we can feel that small of a change. What I am interested seems to lie in _how high for how long being in an airbone state before one has to correct significantly_, which of course is directly correlated to the suspension setup, the speed over the bump, the traction and the properties of the tire rubber at that moment.
> 
> I think I ponder on this too much. Just that it's exciting to understand the car's behavior from a physics POV.


Jack one side of the car. See how far you have to jack it to get both tires off the ground. THAT is how far you have to roll to get both wheels off the ground. Sit in the seat, look out the lower window, what do you see? At speed it will appear worse.

Stock suspension and lifting wheels off the ground normally is just before the entire car rolls over and plays dead. You need a LOT of roll stiffness to lift even one corner. You are not even close. And a LOT of stick. Again, not close.

Also figure, to roll enough to lift one entire side off the ground requires 100% weight transfer, and you don't have the tires to do that. You need to look at track width, CG height and max G the tires can generate. At 1 G, you would need the CG height to be at or above 1/2 the track width, and that ain't so. From the physics POV.


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## liuk3 (May 3, 2004)

Mr Paddle.Shift said:


> I am off to another event at the same location next week. I will post my findings.


does someone need to attend their trackaholics anonymous sessions again?


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## SergioK (Aug 14, 2002)

Mr Paddle.Shift said:


> I am off to another event at the same location next week. I will post my findings.


Who with? How much? I want to get back to BW since I have no more events slated til the BMW CCA BW next year.


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## Mr Paddle.Shift (Dec 19, 2001)

Thanks for the insight, Chuck!



CSBM5 said:


> Re open diffs...it's been many years since I've tracked a car with an open diff, but you'll find that if you take out some rear roll stiffness (maybe go to a higher rate rear spring to compensate, etc.), you get better inside wheel traction off the turns. Also, if you have the room, opening up the steering lock just a bit as you ease off the throttle can help you regain traction and get back into the throttle on track out (i.e. turn 2 at VIR).
> 
> Once you add a LSD to the car, you will likely find that you need to retune the suspension to take out understeer which is now apparent with the rear end hooked up better.
> 
> Chuck


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## Mr Paddle.Shift (Dec 19, 2001)

Got it. I agree that a stationary roll and a dynamic roll will be quite different, since the latter involves a velocity motion of the vehicle as well.

Btw, is roll center more appropriate in this equation than CG?

I am curious why track width is part of the equation. Cos the way I look at this is treating the car as a see-saw adjacent to the car's lateral axis. And the bump is seen as a disturbance that causes a moment about the roll center. Then the moment transfers a lateral load from one end to the other. Assuming on the extreme case that the shocks and springs are replaced by solid rods and that the tire/wheel combo is one huge solid disc, then by theory most of the force caused by the bump should be transferred entirely to the other side.

I am actually guilty of not revealing earlier. I do have the Millikens' Race Car Vehicle Dynamics bible which I read to sleep every other night.  But at this point, I want to develop more "feel" to understand the theory. Your feedback has been very helpful. Thanks. :thumbup:



Pinecone said:


> Jack one side of the car. See how far you have to jack it to get both tires off the ground. THAT is how far you have to roll to get both wheels off the ground. Sit in the seat, look out the lower window, what do you see? At speed it will appear worse.
> 
> Stock suspension and lifting wheels off the ground normally is just before the entire car rolls over and plays dead. You need a LOT of roll stiffness to lift even one corner. You are not even close. And a LOT of stick. Again, not close.
> 
> Also figure, to roll enough to lift one entire side off the ground requires 100% weight transfer, and you don't have the tires to do that. You need to look at track width, CG height and max G the tires can generate. At 1 G, you would need the CG height to be at or above 1/2 the track width, and that ain't so. From the physics POV.


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## Mr Paddle.Shift (Dec 19, 2001)

liuk3 said:


> does someone need to attend their trackaholics anonymous sessions again?


"Hi my name is VS and I am a trackaholic."



SergioK said:


> Who with? How much? I want to get back to BW since I have no more events slated til the BMW CCA BW next year.


SpeedVentures. $170. And guess what? We are running the extended ButtonHook. Yeah!


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## Pinecone (Apr 3, 2002)

Mr Paddle.Shift said:


> Got it. I agree that a stationary roll and a dynamic roll will be quite different, since the latter involves a velocity motion of the vehicle as well.
> 
> Btw, is roll center more appropriate in this equation than CG?
> 
> ...


Force acts upon the CG, which causes roll about the roll centers. But the opposing force is at ground level (tire contact patch) at 1/2 the track width away, the roll center height doesn't have anything to do with weight transfer per se.

Track width has to do with weight transfer, the wider the track, the less the weight transfer. That is why one way they have used to try and slow F1 cars down, was to limit overall width. Simple vector. CG height provides the lever arm to cause roll, the 1/2 track width provides the lever arm to resist roll.

Actually if you truely model the suspension the lever arm to resist roll is a line from teh roll center to the tire contact patch, but the length is pretty much the same for any reasonable roll center height.

But to lift wheels you have to have 100% weight transfer, so all these do factor in to try to do waht you think you are doing.

Paul Van Valkenburg's book is an easier read.


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## Mr Paddle.Shift (Dec 19, 2001)

But of course... I just got my sense checked in about _track width_. I was thinking of the width of the track road! :tsk: In that case, yes, track width and CG height determine the lateral load transfer.

I actually read the Van Valkenburg's and Herb Adam's books. Definitely easier to grasp but both lack the mathematics I am looking for. I just wished I had done more of this during my undergraduate years.



Pinecone said:


> Force acts upon the CG, which causes roll about the roll centers. But the opposing force is at ground level (tire contact patch) at 1/2 the track width away, the roll center height doesn't have anything to do with weight transfer per se.
> 
> Track width has to do with weight transfer, the wider the track, the less the weight transfer. That is why one way they have used to try and slow F1 cars down, was to limit overall width. Simple vector. CG height provides the lever arm to cause roll, the 1/2 track width provides the lever arm to resist roll.
> 
> ...


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## TeamM3 (Dec 24, 2002)

Mr Paddle.Shift said:


> Not driving hard enough!


fwiw, you never even stated that wheelspin was your issue, I suppose you were expecting me to draw an ignorant conclusion too :dunno:


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## Pinecone (Apr 3, 2002)

Exactly. No wheel spin, lack of LSD is not a problem.


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## ayn (Dec 19, 2001)

Mr Paddle.Shift said:


> Or should I get a STi/Evo? I get a feeling that I will enjoy driving one of these.


Yup, I thought about modding and adding LSD to my 330Ci, but bought an EvoMR instead.


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