I seen this too and just thought they were marking their corners.

Paul

 

Tremec is correct, "it is a bit more complicated". Any wheel that lifts during hard cornering is not adding to cornering power, period. But, all things considered, Balance, and, cornering power, the Mini made 'need' to lift its rear wheel as a trade-off to rotation. further, a stiffer rear bar will as Tremec wrote, will cause the rear wheel to lift more so than a stock set-up, but will help the Mini rotate quicker...the real role a sway bar should be used to play...again, as Tremec wrote.

 

Well that too

 

Tremec, but if you look at the pictures dont you think there is a lot of roll in the front end of the car? I mean if you look at the position of the rear wheels in comparison to each other they seem pretty flat. Now look at at the front, it seems like there is a lot of roll. For auto cross this weight transfer probably wouldnt be so bad cause you would like the car to pivot, but I think if you were tracking your car you would want something a little more stable under braking.

I think overall like you guys said its just the nature of the beast, Im not trying to challenge Tremec or anyone else and say they're wrong im simply just throwing some other ideas out there that I think should be considered :smile:.

 

I enjoy the discussion I have heard that the stiffer front bar induces front end plow I havent tried one personally tho anyone out there have a stiffer front bar?

 

Sway bars are used to change balance; simplified, understeer vs oversteer. A larger rear bar will help to keep a Mini's front wheels planted and increase oversteer. The reverse is also true; a larger front bar will keep the Mini's inside rear wheel from lifting to a degree determined by the size of the bar and induce more understeer, again, simplified. Also, the larger the bars, the quicker the reaction to steering inputs; if you were to increase the size of both stock sway bars by 50% for example, balance would remain the same, but the car would react wickedly quick to steering input and corner with much less roll. Cornering balance and raw grip must be balance to suit driver needs and ability, and the car's inheent limitations. Also, a Mini set up for one track may not work well on another and niether will likely work well on the street.

Personally I feel the Mini has great high speed stability but does understeer a tad too much in slow corners. If I were able to adjust a bit more bound and rebound into the rear dampers, I would leave the sway bars alone. But alas, I cannot. I'm waiting for the Works Suspension kit...I want to see how this kit differs from the stock suspension. The Mini is pretty damn good from the factory as a daily driver, however...maybe too much dive and squat but that's about it.

 

I can atest to this from experience. I had my car setup so the balance was very, very good. Then I added a stiffer front sway bar and leaving all else alone, there was a noticeable increase in understeer. To correct this I will probably have to go to the final stiffest setting on the rear bar. But the car is so stiff now, it will lift a wheel off the ground when entering most driveways at an angle, or when crossing dips at an angle in the road, including the front wheels. I know because I get wheel spin when exiting the parking lot from work each day.

 

and you will find a benefit to all that stiffness; when you jack up the car to rotate your tires from either the front or the rear jack points, that side of tires will will lift off the ground allowing a complete front to rear change in one easy step. Otherwise, this can be a bit annoying on public roads. There is such a thing as too stiff.

 

Never too stiff! If I jack from the front point the rear lifts off the ground at exactly the same point as the front

 

agreed - never too stiff

oh my, this could get in the gutter fast!

 

get me a welder! I'm locking it all down. Zero degrees of deflection in turns! Who needs active suspension!

 

Is this stiff enough?

 

I was so proud of myself for not going there on my last post

 

I think the title says it all

 

so the stiffer the better...ehm!

 

That's what she said!

 

Ok officially in the gutter now

 

Viagra impregnated dampers, very stiff. Now that that's out of my brain...

 

I was thinking about this some more. It seems to me that if you had a car with the center of gravity below the roll center, it would actually lean into the turns. If you had a car with the roll center and center of mass at the same height, there would be no lever, and the car would stay flat. In this case, very soft springs would be nice, as there would be more suspension compliance.

Isn't the perfect car one with soft springs (so that each tire can respond independantly to surface irregularites), very low unsprung weight (so that the wheels can respond quickly). and a rool center at the height of the center of mass (flat through turns)?

With the mini, the center of mass is pretty much fixed. The roll center is pretty much as well, so we're stuck with it's tendancies to lean. Nothing to do about that without a torch !

So stiffer seems to be a compramise because of the basic design compramises of the suspension geometry.

And despite the jokes aobut the Pontiac, it's stiff, but very well balanced. Here, we're talking about changing the bias of the sway bars (unbalenceing the sway bars) to make up for bad geometry. So I'm back to thinking the camber plates are the way to start (attack what you can in geometry, then tune what's left). Seems like coil overs will help as well, as they can be used to change the ride height of the front and back as well, attacking more of the issues with geometry. Is the center of mass of the mini so high that the best thing is just to get it low? And does this mean that you need stiffer springs because of limits to suspension travel?

Am I all confused here?

 

you are a little confused. Centrifical force is what actually causes lean - things in motion tend to stay in motion. So, as the tires build up cornering force, the rest of the car attempts to leave the chassis. Imagine a car whos body was not mechanically attached to the chassis. If the car accelerated in a straight line very quickly, the body might fall off the back of the chassis. Same is true when cornering; the body would maintain its motion and go straight when the chassis turned. Just how a car responds to external forces depends upon center of gravity, its roll center, roll couple, weight distribution, suspension design and tire compound...among other things. Everything is a trade-off and there is no perfect car. The perfect car would defy the physical forces that define our world. We are bound, inextricably, to these forces.

The Mini is a damn good car. slightly stiffer springs, more sophisticated dampers and a larger rear bar might make it better. Some more neg. camber up front but not a lot.

 

I don't think it's that simple. Centrifugal force in and of itself would not cause lean. What causes the lean is the force of the tire's grip on the road coupling with the centrifugal force of the corner. They are in opposite directions but acting off-axis from one another, causing a torque which makes the body lean.

 

There's also the lever arm. the lean is because the center of mass is higher than the axis of rotation, so there is a moment, and the resulting torque rotates the car about the axis of rotation, to the extent that the torque is counteracted by the change in forces in the springs. that's why the center of mass heigth is important.

I understand the force vectors (I'm a phycist). In thinking more, it seems that even with perfect geometry (no net torque around the axis of rotation), the inherent compramise is between complience (soft springs to soak up bumps) and response time (tighter suspensions to improve weight transfer). Soft suspensions will allow each wheel to act more independantly, maximizing the contact area of the tire. But soft suspensions take a long time to load up with weight transfer.

For those that know suspension geometry stuff, if you have an "idea" center of mass location relative to the axis of rotation, does a soft suspension still take time to load?

Matt

 

Here's my take...
The ideal would be where the CG is directly on the road. This would create no moment (torque) around the outer wheels and the only force acting on the car is the centripital acceleration of the car against the frictional force of the tires. When the CG is above the road, the moment that is created must be taken and added to the force the car exerts on the road. The moment of the car in the turn is taken on the outside wheel. This moment will be put downward on the suspension and tires, thus forcing the suspension the compress and induce body roll. Adding more reinforcement to the suspension will reduce this effect and make the car handle better.

 

centrifical force is what causes lean. Yes, tire grip results in a torque in some other direction (vector) that causes a centrifical force to become alive. So, the two working together cause lean...or else, all would remain still.

It is sort of impossible to write in depth; I don't have the time or space, and, I'm not a suspension engineer or physist. But, having studied physics in college for a few years and observing that physics attempts to describe almost every action in this world leaves me with some fundamental understanding for the forces at work. But you are correct, the tires are definately part of the equation.

I must say, Motering.com is a very friendly place to express ideas, thoughts and experiences. I can think of a few other .coms whos members might actually become somewhat angry and sarchastic toward my simplistic responses. I only mean to help.

 

Centrifugal force is a mis-nomer. It's really centripital acceleration. But it's really the same thing! The tires do provide the turning force, and that force is directed (pretty much) perpendicular to the direction of motion, hence the turn! but remember the force diagrams. The traction at the contact patch id directed laterally inward at the surface of the road. This provides torques on the control arms. This is the force that creates side-wall deflection. So the control arms hold the wheel in the correct (one hopes) virticle plane. The forces that move the car are trasferred via the control arms to the chassis (or whaever they are bolted to). the lever arms still come into play. Imagine, if you will, a very funky suspension with the two control arms a foot or two ABOVE the wheel hub. If this point is still ABOVE the center of mass, the center of mass would swing outward, and the car would lean in! not that anyone would want to do this for a street car....


Anyway, I think I'm finally getting my prioritization down:

1) Geometry (Camber plates, and there were some coil overs on ebay for $550)

2) Tires, wheels and brakes.

3) Sway bars....

2 and 3 may switch, based on $. But is seems that all roads lead to the same place:

different springs (coil overs if you have $), different sway bars, camber plates, and get rid of the run flats! Whether you have to go with a stiffer bar in front, and if you need ajustment in the control arms out back, seem to be details particular to individual set-ups!

Matt