DrivenAP2

So I have read a lot of different posts on suspension setup on S2000, and I can't rap my head around this.

If you lower the car both the upper, and lower control arms move up. If you install a taller lower ball joint you can correct the travel of the lower arm, but do nothing for the upper arm.

So my question is... How do the roll center adjusters improve anything? With the upper arms off their natural line, and it's pivot point already at a point that it wouldn't normally be, unless under load... would more load from that point cause awkward/unpredictable movement? Especially with the lower arm on a different pivot point?

I'm most likely wrong but it seems to me these don't really help much and, Alignment, spring rate, and swaybars would be a better way to compensate for ride height geometry changes.

I think this works out how to measure to find new roll center.




This helps a little, but I'm still sure that it's messing with the cars natural state by changing the arm pivot points. Or the way the arms travel together.



Anyway... if someone could shed some light on that, or just point me in the right direction that would be great.

tama05

Roll center adjusters will help bring back the to more of a natural state similar to stock with the car lowered. They will also allow for more camber adjustment and more shock travel which will not create an unpredictable movement. Also once these are installed it's pretty much required to have an alignment to help dial in everything to its proper setting as they will throw of toe and camber. The corrected position of the lower arm will raise the cars roll center and create less body roll at a lowered position. Stiffer spring rates can help as well if you decide not to install them but a corner balance will help with keeping even weight distribution so that your car feels more predictable without being too tail happy. Also depending how you drive the car and what you want out of it will determine how far you go into modifying the suspension. Check out rob robbinette's page for tons of information on all kinds of suspension modifications. Hope this helps.

Gottabfast

Quick answer with no pics: roll center isn't the only point that matters. When you lower the car, the CG drops, which is great in general. The roll center also changes because of the angle of the arms. The distance between the roll center and the center of gravity is called the roll couple. If the distance between the CG and roll center increases, the roll couple increases. An increased roll couple is the lever arm for roll - longer lever arm means more roll (same way using a bigger breaker bar means more torque to loosen a bolt). Understanding that the suspension moves in an arc (gaining positive or negative camber as the car rolls) is key.

Suspensions are designed to gain negative camber as you roll. If the geometry is compromised, you will gain positive camber as the car rolls - which will remove available grip by keeping less of the tire in contact with the road during cornering.

Roll center adjusters will help to restore the suspension attachment point angles relative to the body and correct the arc of movement back to stock. This will decrease the effect of the suspension working against itself under roll and improve the contact patch during cornering.

To truly understand, pics and research will help. Sport Compact Car's Mike Kojima wrote some good articles with easy to understand diagrams.

DrivenAP2

You guys are right, but not really what I'm trying to understand. I have read almost all of the things suggested, as was as a couple of race suspension setup books, I'm also a tech... So I know how to, and why to align a car. Knowing all this is what led to my misunderstanding. You can't only correct half of a situation. Something I didn't think about was the increase in dampener travel witch is awesome, but the upper arm is still in a much different position than it should be. I saw the modified build where the made adjustable upper control arm mounts, witch as far as I can tell is the only way to truly correct the issue. Or maybe a shorter upper arm to compensate for the change in arm travel distance. Or it may be a complete none issue, and that's really I guess what I want to know. Is the upper arm being on a different plain then the lower arm really that big of a deal?

gptoyz

This is an excerpt from RobRob's page:

"The roll center is the point the chassis rolls around when it leans around a corner.

The distance between the roll center and the center of mass is called the roll moment arm (see diagram below). The greater the distance between the roll center and the center of mass, the longer the lever centrifugal force has to work with to roll the body. Think of the roll moment arm as a lever that runs upward from the roll center. Centrifugal force grabs the lever at the center of mass and pushes the lever toward the outside of the turn and rolls the chassis. The longer the lever the easier it is to roll the car.

Shortening the roll moment arm, by raising the roll center or lowering the center of mass, will reduce chassis roll. Taken to the extreme if the roll center and center of mass are in the same spot then the chassis will not roll when going around a corner.

When an S2000's suspension is lowered it's roll center is lowered more than the center of mass which increases the length of the roll moment arm which makes the car roll more than when running at stock height (assuming same spring rates)."

the page and the rest of the content can be found here:
http://robrobinette.com/S2000RollCenters.htm

"I'm most likely wrong but it seems to me these don't really help much and, Alignment, spring rate, and swaybars would be a better way to compensate for ride height geometry changes."

-the purpose of alignment is to maximize tire contact patch for a given scenario. 2 cars using the same suspension components and same ride height can utilize 2 different alignments based 2 different race track configurations (low speed, frequent side to side transitions vs high speed sustained corners with few transitions)
-spring rate or spring frequency should be chosen to soak up the imperfections on the surface you drive (primarily) and partly to account for static body roll resistance
-the sway bar is also a body roll reduction device, but it links left and right side together which reduces the ability of the suspension to act independently to asymmetric imperfections

You are right, you can't correct half of the equation. But exactly what situation are we dealing with here? Class, budget and chassis will determine what kind of tools you have in your tool box to fix the problem that you are trying to correct.

Let's take the s2000 in a fairly restrictive class that only allows COILOVERS, OFFSET BALLJOINTS and ROLL CENTER ADJUSTING PLATES. In the ideal world you would have at your disposal, adjustable toe arms, adjustable control arms, eccentric bushings and adjustable suspension pick up points, but in this scenario we are limited to the tool box options stated previously. If our modified roll center is moved, the only way to move it back in place would be a static roll center adjustment plate.

DrivenAP2

As it turns out I have read Rob's page... at least a few times.

Ok basically it seems you would have to have a race teams budget to correct the issue properly. Well thanks for your help guys.

gptoyz

Well that's the case with any inherit problem. It takes bucks to fix. The band aid fix is to either bring the car as low as possible without moving roll center too excessively or use a vanilla plate to adjust the geometry back in place




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DrivenAP2

At this point i don't think lowering the car is even an option for me. I was playing around with a suspension geometry calculator last night, and watching what happens when you correct one arm and not the other. The arc of the upper arm does some wicked things to camper gain and loss.

Better tires, and I think the coilovers I want should allow me to keep the stock ride height.

What is a vanilla plate?

Sebring AP1

Is the concern here that the geometry changes as you lower the car?

There is more to be gained by lowering the car and using RCA than leaving it at stock height, if that's what you're wondering. Yes, things change - but look at the larger picture here. Everything you change on the car is a give and take in some area. You make the changes that get you where you want to be.

Certain cars use OEM pickup points and are insanely fast. They largely use RCA/lowering and basic (not crazy expensive) methods to realign geometry. The FXMD NSX is a good example of this.

s2000Junky

Its not that complicated, but this thread sure is trying to make it that way. The upper control arms are shorter then the bottom, that right there is going to make the wheel camber in as it compresses (nevermind the different connecting point plane between upper/lower which also compounds this) which is what you want. Lowering the car will further increase that rate, its easy to visualize when you look at the diagram above. Simply lengthening or shorting the upper control arm will alter this rate. To me the lower roll center adjuster isn't needed on this car to net any positive results if your lowering the typical -2" -1.5". An adjustable toe arm is however, becuase an increase in toe relative to susp movement is a negative attribute.