This is TRUE!

My 2005 MCS with LSD does the same thing. MY old 2002 MCS did not! It's NOT the alignment.

David

 

Meb and everyone,

A very enlightening discussion. Thanks. The roll center issue is one that was only briefly touched on and is worthy of a little more discussion.

The roll center of the stock MINi is lowered rather drastically through the combination of additional negative wheel camber and lowering springs. Who cares? MINI cares. The roll couple, the impact of cornering forces on the center of gravity (CG), is magnified as the roll center is lowered. Front roll stiffness is reduced, even with no changes to the spring and roll bar rates. I think that this phenomenon is why some track drivers require stiffer front roll bars in their lowered MINI's to get a reasonable balance between the front and rear suspension roll rates and to reduce unwanted front tire camber changes in cornering. Compensatory increases in front spring rates and/or roll bar rates to restore roll rates can reduce wheel compliance and have a tendency to convert your MINI independent front suspension to a virtual solid axle configuration.

Shims at the outer ball joint and the inner ball joint mounting points that restore the control arm angle, the inboard balljoint tilted upward toward the top strut mount, will raise the roll center and restore the roll center to a point closer to the stock setting. The front roll rate will be substantially increased compared to the unrestored geometry. Spring rate and roll bar rates may not need to be changed to achieve suspension balance.

Am interested in other's thoughts and observations.

This un-anticipated change in roll rate gets back to the truism that it is easy to accidentally disturb the nice equilibrium of MINI's front-end design thru careless modifications.

Regards,
John Petrich in Seattle

 

Hey John,

I think you know I'm with you 110%. Roll couple is indeed another aspect to pay lots of attention to for all the reasons I've previously posted about, and as well, for all your observations.

It is extremely difficult to describe the interrelationships between every physical aspect of suspension theory and practice. I avoided writing in depth about roll couple above - only mentioning it once - because it like everything else, is a huge subject...especially in this format.

Here are my thoughts in no particular order;

. Control roll centers, meaning, do not exaserbate thier dark side.
. Maintain stock scrub relationships, especially with a strut type
suspension. Long and short arm systems leave us with more opportunity, but are complicated to design and develope. Honda no longer uses this type of suspension on their cheaper Civic models.
. Use sway bars as a fine tuning mechanism and not to cure roll problems wether real or percieved.
. select spring and damping rates before all else. This will affect all the above either in a positive or negative way...depending upon what you pay attention to.

I'm outta time this morning, more later.

Thanks for you input John!

Okay, have more time;

 

Thanks to both John and Meb. This is one of the more informative threads I can remember.

Great stuff. This is what makes NAM so cool.

 

I read this post when it first came out, and didn't comment as the alignment experts seemed to have it nailed for an explanation. Also, I thought I may magically start thinking I had a problem the more I got into reading this thread.

But below information is just more data for this issue

However, my january 2005 with lsd does this too, I have the jcw suspension (aligned at bmw facility prior to delivery, drives wonderfully which tracks straight, no apparent bad habits when driving normally on a flat road, etc) jcw package, and < 11 pound wheels... Funny thing is that it only happens under full low speed acceleration. for example going up hill in 2nd gear when I hit about 5k... pulls to both sides depending on roadway smoothness with torque.. which I don't like.. I assumed this is a LSD issue with higher horsepower application..

So, anyone out there with the factory lsd and 15+% pully with cai, etc... have residual feelings of torque steer under full throttle,? Or should I assume my alignment is poor

 

Yes!! This is very educational. Thanks for the techincal details. I now have a better appreciation for how changing one seeming small thing like wheel offset can adversely effect handling. I mean I knew offset would change handling but now I better understand why which is more important.

 

I'll add that tire side wall stiffness and tread squirm can affect steering under full throttle applications. I just installed Michelin's Pilot Exalto PE2s. I previously thought these tires had very soft sidewalls but now believe it is the tread. Anyway, torque steer is reduce dramitically, tramlining is all but gone, but also, is the ability to control path accuracy with the throttle. It's a trade off.

Stiff tires - runflats - will transfer wide open throttle energy more directly to the road. And honestly, I do not know how effective the stock LSD is...is it more marketing than content? Should it be stronger? In theory, a strong LSD will affect turn-in...may make the turning radius wider and the effort higher.

I've never used one, agreeing with one instructor; if you're really smooth you don't need one. I'll never know.

 

I guess he must mean no throttle in corners. A good driver with LSD will beat a good driver without. Every time. Without trying to start an arguement, if you're smooth enough you don't need brakes, either.

Look at autocross results across the country. SInce the lsd came out from the factory the MCS has become a PAX killer. There was even serious thought given to moving the MCS up 3 classes due to the lsd.

 

Of course an lsd will help at very low speeds and tight turn radii. Meb's instructor was talking about the track, not autocross.

 

I would have to assume so since we were on a track- LRP. And, I have no backdrop to judge an LSD - for a front wheel driver. Really, I've never used one, just never had the opportunity. It's not a like or dislike thing for me. I would love to try one on two otherwise similar cars.

Curiously, is the LSD offered for the Mini a clutch type? This might account for uneven torque distribution especially in wet conditions.

 

I think it's a cone type LSD. I did a search & came up with these cone types.

Chuck

 

On a road course you can not get a MCS without a LSD off the corner without doing burn outs. The cold true is you can not put all the power down as you track out past the apex.

David
Approved Instructor For:
PCA, BMWCCA, Ferrari Club Of America, Ferrari Owners Club, PDA, TracQuest
2005 MCS LSD
Past 2002 MCS w/o LSD
Track Car 1993 911 RS America
http://members.rennlist.com/davidk/DLK_MCSLRP902.jpg
http://www.rsamerica.net/gallery/davidk_of_nj.htm

 

Burn outs. Cool.

 

But not fast.

 

Nice

 

I would think this has lots to do with the course...but then again, one apex can be found at just about any course. Makes me wonder then, if an adjustable LSD is better?

 

jlm,

I sent you a PM about this. But, I forgot about the bearing, damn! As the wheel is turned, the body lifts - as you know. Could this simple lifting cause the bearing to deflect? Intuitively, I feel the compression stroke will yield more so than the weight of the body???

 

the bearing flex comes from the camber changing and/or the precessing. In my measuerments, with no springs mounted, there is very little camber change over the full compression range. Body lift during precessing...it seems like a little more contribution than steering rake angle effect.

 

Okay...have you had the chance to measure camber values at full lock left to right as well simulating ride height and full compression? I have to admit, I'm sort of stumped by this one...I feel like I'm circling in, but everytime I get close I lose it...

Ya got a kinematics program laying around anywhere?

Michael

 

Certainly 225's and scrub radius could cause this, the suspension geometry issues are well discussed.

Another thing to consider:
If the Control arm bushings or inner ball joints are worn, LSD puts more power to the wheels and the car will toe out signifigantly with an LSD.

I found on other LSD FWD cars running 225 "DOT" Rcomps that slight differences in tire pressure would cause torque steer at high speeds due to the LSD seeing different grip in the tires.

Remember when your evaluating suspension drivability.

1st. equal tire pressure and tread side to side.
2nd. alignment setup to a know value and even side to side.
3rd. understand what is changed from stock, and how it all relates.

be careful assuming what is causing a problem, if you can correct the suspect situation and test to see if the problem is reduced. Keep an open mind though, even if it gets better, you may just be fixing the symptom and not addressing the actual problem.