Originally Posted by JETPILOT

How much are you lowered?

Did you have to raise the height of your coilover?

Do you have a choice of how much you want to adjust the roll center? Different size spacers?

Originally Posted by Z1 Performance

2 different size spacers are included depending how much the car is lowered

I should have my car back Monday night guys, had to do some modding to fit my new camber arms

Originally Posted by bimmertech

as nice as raising the front roll center would be(used this technique on mustangs for years now) i will prolly just wait until an adjustable thrust rod comes to market and adjust the roll axis that way.

Originally Posted by Colin_S

Adam, not sure that is correct. Yes there were 2 sizes of spacers in the box but both are needed, one goes on the ball joint and the other goes on at one of the other bolts on the arm. It shows you in the pics on those Japanese instructions.

Jetpilot, the way there work are (if you excuse my non-technical explanation) you change the ball joint and slide the spacer over. Then when the ball joint is bolted back up the arm sits lower as the spacer is now in. The ball joints pivot points are designed to allow for this difference. Also at another point you need to fit another spacer to allow one of the other bits to bolt onto the lower arm.

Originally Posted by Beau

How does an adjustable thrust rod affect roll center? I can't picture how that works.

Originally Posted by http://en.wikipedia.org/wiki/Roll_center

Theory

There are two definitions of roll center. The most commonly used is the geometric (or kinematic) roll center, whereas the Society of Automotive Engineers uses a force based definition.

The location of the geometric roll center is solely dictated by the suspension geometry. The SAE definition of the force based roll center is "The point in the transverse vertical plane through any pair of wheel centers at which lateral forces may be applied to the sprung mass without producing suspension roll".

The lateral location of the roll center is typically located at the centerline of the vehicle when the suspension on left and right sides of the car are mirror images of each other, and in identical locations.

The significance of the roll center can only be appreciated when the vehicle's center of mass is also considered. If there is a difference between the position of the center of mass and the roll center a “moment arm” is created. When the vehicle experiences angular acceleration due to cornering the size of the moment arm, combined with the stiffness of the springs and anti-roll bars (anti-sway bars in some parts of the world) dictate how much the vehicle will roll while cornering. This has other effects too such as dynamic load transfer.

Application

Load transfer is of critical importance for vehicle stability in vehicle such as SUVs. Ideally in high performance applications load transfer tends to be minimised as a tyre's performance is directly affected by the amount of load that it has to transmit. In a steady state turn the final load transfer, summed across all the axles, is only related to the position of the center of mass above the ground, the track width and the lateral acceleration. SUVs must shift their center of mass lower or decrease their lateral acceleration to avoid tipping. To keep them from tipping many auto manufacturer use tyres with lower grip to reduce the vehicles cornering capacity, or the roll stiffness balance front to rear can be altered to encourage understeer or oversteer as necessary to limit the maximum lateral acceleration of the vehicle.

The geometric roll center of the vehicle can be found by following basic geometrical procedures when the vehicle is static. However, when the vehicle rolls the roll centers migrate. It is this movement of roll centers that vehicle dynamicists seek to control and in most cases limit. The rapid movement of roll centers when the system experiences small displacements can lead to stability problems with the vehicle. The roll center height has been shown to affect behaviour at the inititation of turns such as nimbleness and initial roll control.

Testing Methods

Current methods of analyzing individual wheel instant centers have yielded more intuitive results of the effects of non-rolling weight transfer effects. This type of analysis is better known as the lateral-anti method. This is where one takes the individual instant center locations of each corner of the car and then calculates the resultant vertical reaction vector due to lateral force. This value then is taken into account in the calculation of a jacking force and lateral weight transfer. This method works particularly well in circumstances where there are asymmetries in left to right suspension geometry.

The practical equivalent of the above is to push laterally at the tire contact patch and measure the ratio of the change in vertical load to the horizontal force.