Glossary
What is a Roll Centre? Definition, Height Effects & How to Change It
The roll centre is the imaginary point in the vertical plane of an axle about which the sprung mass rotates when the car rolls. Its height is determined by the suspension arm angles. The distance between the roll centre and the centre of gravity is the roll moment arm: a lower roll centre means a longer arm and more body roll for a given lateral force, while a higher roll centre transfers more load through the suspension links rather than the springs.
| Change | Body roll | Geometric load transfer | Typical feel |
|---|---|---|---|
| Raise front RC | Less | More, faster | Sharper turn-in, can feel edgy |
| Lower front RC | More | Less, slower | Smoother, more progressive front |
| Raise rear RC | Less rear roll | More rear geometric transfer | More rear grip initially, can snap |
| Lower rear RC | More rear roll | Less | Better traction out of slow corners |
Finding the roll centre
For a double wishbone, extend the upper and lower arm lines until they meet at the instant centre, then draw a line from the tyre contact patch to that instant centre. Where that line crosses the car's centreline is the roll centre. Repeat for both sides; with symmetrical geometry they coincide. Setup Genius includes a roll centre and CG height calculator that performs this construction from your pickup point coordinates.
Roll centre migration
As the car rolls and heaves, the arm angles change and the roll centre moves, sometimes by a large amount and sideways as well as vertically. Lowering a car on its stock arms often drops the roll centre below ground, lengthening the roll moment arm and making the car roll more despite the lower CG. Correcting that with extended ball joints or relocated pickup points is a common upgrade.
Frequently asked questions
Is a higher roll centre better?
Not simply. It reduces roll and speeds up load transfer, but it increases jacking forces that lift the car in corners and can make the tyre load spike. Most designers keep front roll centres low and the roll axis inclined slightly nose-down.
What is the roll axis?
The line connecting the front and rear roll centres. The sprung mass rolls about this axis, and its inclination influences front-to-rear balance.
How does ride height affect roll centre?
Lowering the chassis changes the arm angles. On most road-based suspensions the roll centre drops faster than the CG, which increases body roll.
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