for 2002-2006 R50 MINI Cooper, R53 Cooper S, and 2005-20008 R52 Convertibles.


The PRECISION STEERING AMPLIFIER (p/n NMS6000) improves front suspension geometry for better handling and car control. Works well with stock suspension on and off the track, and even more effective on lowered MINIs. The PSA is “track-tested” following complex computer simulation models.  Even temperatures across the tire following track sessions support the improved dynamics of the front suspension with the PSA installed.

The PSA is compatible with your 2002-2006 R50 MINI Cooper, R53 Cooper S, and R52 MINI Convertibles. Requires 17" wheels or larger.

Precision Steering Amplifier How it works:
The Roll Center Axis of an automobile plays the major role in providing feedback to the driver. An Axis drawn between the Roll Center for the front suspension and the Roll Center for the rear suspension is called the Roll Center Axis. The drivers perception of the direction that the automobile is moving , yaw and roll, is determined by the Roll Center Axis motion. The front and rear Roll Centers are points that the car is actually rotating about, and is determined by the front and rear suspension geometry.

A primary objective in the design of a performance automobile is to have the front and rear Roll Centers maintained close to center of the car (that is, the left to right center) and vertically position above the ground. As an automobile is maneuvered the front and rear Roll Centers move left and right as well as up and down and hence the Roll Center Axis moves accordingly. The feedback to the driver about the motion of the car is based on motion sensing relative to the Roll Center Axis. The Roll Center Axis is the true Axis of roll and yaw.

Computer simulation models were used extensively to study the R53 MINI Cooper S suspension. The Roll Center on the front suspension of MINI Cooper S has large left right position changes when cornering. This is particularly true and evident in MINI’s that have been lowered. The result is poor feedback to the driver and poor handling characteristics.

This Roll Center movement can be significantly reduced by lowering the front ball joints. The PSA was created to correct this problem and to significantly reduce the front Roll Center motion during cornering. The PSA is installed between the ball joint and its mounting surface on the hub carrier. The result is dramatically improved handling characteristics on street and competition MINIs. The improved feedback to the driver is significant. The roll center movement is substantially reduced by lowering the ball joints as has been verified by calculations and computer simulations, and proven on the track.

The Data:

The table below shows the roll center movement of the MINI for the stock position at 6" above ground and the lowered ball joint at 5.18 " above ground ( lowered by .82"). This data table was generated from a computer simulation of the MINI Cooper S suspension. A brief explanation of the table follows.

Ride is the ride height change from static height of the MINI

Roll is he body roll angle of the MINI

Steer is the steering angle input

X and Y are the horizontal and vertical position of the roll center X=0 Y=0 is at ground level at the center of the MINI

Camber L and Camber R are the camber changes for the left wheel & right wheel

The rows from the first row to the last show the dynamic changes that occur for a typical turn. With an explanation of the first 4 rows you should be able to understand how the remaining rows relate to the dynamic changes that occur for a MINI turning.

Row 1 shows the MINI in a static position

Row 2 shows braking first which causes the ride height to decrease.

Row 3 shows the beginning of the turn off the brakes, front rises a bit, the beginning of steering input and some roll

Row 4 show further into the turn, body rises and rolls a bit more with more steering input.


Precision Steering Amplifier Data

The Analysis:

The changes in the X and Y (the roll center position) and the camber changes are of significance. In particular, note the range for the horizontal roll center X for the stock ball joint from -39 to + 40 right in the middle of the turn. Recognize that this is the feedback the driver is feeling as the roll center moves from one side to the other (about 80" of movement). Now contrast this with the horizontal movement of the roll center for the lowered ball joint suspension and note that the total movement is only 11.8" and the center never moves from one side to the other side.

This is not only a great improvement in the diver feedback, but it is also an improvement in the suspension geometry. In addition, the effective spring rates are also increased due to the shorter moment arms acting through the roll center. The roll center Y dimension has also been improved in that it is never negative (negative means below ground level), and has been raised. This improves the effective roll stiffness by increasing it. The camber changes were studied to confirm that the changes with the lowered ball joints did not adversely affect the handling. Further study of the table should give you an insight into the significant improvements realized from the lowered ball joints.

The Bottom Line:

With the PRECISION STEERING AMPLIFIER installed, your MINI will feel smoother through the corners with better feedback, enabling better control and lower lap times!