“Roll Axis”

When determining the baseline setup for your car, you must determine the front and rear roll centers.   By connecting these two roll centers with a line, you determine the roll axis – important to the overall handling characteristics of the car.  While you cannot normally change the front roll center at the track, the rear roll center can be adjusted in most race cars through movement of the panhard bar.

The front roll center is usually between 0" and 3.5" above the ground, with the rear roll center between 7" and 11" above the ground.  The most common way to adjust the angle of the roll axis is to raise or lower the panhard bar, since changing the instant centers of the front suspension components is a more difficult task.  It is also important to note that the front roll center should never be located any lower than ground level.  This creates a very steep roll axis (rear to front). 

The front roll center should be as close to the ground as possible.  This minimizes the jacking effect, a dynamic situation that pushes the roll center up from the outside tire.  The greater the height of the roll center, the greater the force pushing the car up, away from the track.  This can raise the height of the car, changing the dynamic handling characteristics.

Some rear end suspension systems make adjustment of the rear roll center very difficult.  Again, this is another vote for the use of a three point rear suspension.  Adjustment of the roll center and roll axis is achieved by simply moving the panhard bar.

Mike Loescher is the owner and chief instructor at FinishLine Racing School in Daytona Beach, Florida.  Mike holds Chassis Seminars throughout the year - all around the USA & Canada. View our class schedule or call 386-427-8522 to schedule a private setup date.
 

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