Whiteline Chassis Talk 7 - Caster, what is it and why is it important?

[Whiteline Jim]

An extract from the Whiteline Flatout FAQ on wheel alignment.

A little old and possible overly simplified but good for an overall start.

Caster – What is it and why is it important?Caster is the backward or forward tilt of the steering axis. Vehicle manufacturers are aware of the advantages of caster and as each new model is released the amount of caster specified increases. For example, the VB Commodore was released with around ½ degrees positive castor; the VT now comes standard with around 9 degrees!


Why, because the disadvantages of high levels of castor are being overcome. Rack and pinion steering means less play, lower Ackerman levels, smaller scrub radius (zero is now very common), better and lower profile radial tyres means less sidewall deflection and higher tolerance to greater slip angles. But the greatest obstacle, that of heavy steering effort, has all but disappeared with the universal acceptance of power steering. That’s why Whiteline developed a range of adjustable radius rods for Commodore, which allow an additional 2.5deg positive caster on VB to VS.

High levels of positive caster equate to dynamic negative camber on turn when you need it most. (Have a look at the front wheels of a Mercedes or Audi when parking.) Whiteline continues to put heavy emphasis on additional positive caster when designing new suspension packages.

Caster - "When too much caster is never enough"? – 5 reasons why.

• Maximise tyre contact patch during roll
• Improve turn-in response
• Increase directional stability
• Maximise tyre contact patch during braking and acceleration
• Improved steering feel and self-centre
• Increases dynamic negative camber (on turn)

Castor Vs camber, try castor first. Why?

• Camber doesn’t improve turn-in, positive caster does.
• Camber is not good for tyre wear.
• Camber doesn’t improve directional stability.
• Camber adversely effects braking and acceleration.