Roll Center

Roll center is the pivot point a chassis rolls around at one end of the car. Its height relative to the center of gravity sets how far the body leans and how load moves across the tires.

Also called:

None

In practice

Where it sits depends on your linkage: Hyper Racing puts a panhard bar’s roll center “directly in the center of the bar,” and a Jacob’s ladder’s “where the two center lines created by the strap’s pivot points intersect.” Their tuning shorthand is blunt — “Lower your roll center in the back to make the car tighter. Raise the roll center in the front to make the car tighter.” Vehicle-dynamics people push back on the whole model. OptimumG states flatly that “the suspended mass does not rotate around the kinematic roll axis,” and that “there is little chance the kinematic roll centre would stay in the same position once the car gets some tyre and suspension deflection.” Treat it as a direction-finder, not a fixed point on the ground.

Why it matters

Roll center height decides how much of your spring and shock work actually reaches the tire, so a car built around the wrong one argues with every other change you make.

Go deeper

Read the full post:

Panhard Bar Adjustment and J-Bar Setup: How Height and Angle Change Your Car

Sources

Roll Centers — Hyper Racing — chassis builder’s page on locating roll center and which way to move it front and rear to tighten the car.
Rethink Dirt: Advanced Dirt Track Theory — Hyper Racing — same builder defining roll center as the pivot point the chassis rolls around, and locating it for a panhard bar and a Jacob’s ladder.
Rolling About — OptimumG — vehicle-dynamics consultancy arguing the sprung mass does not rotate about the kinematic roll axis and that the roll centre moves once the car deflects.