Caster, a.k.a. “castor”, is the difference between the angle of the steering block pin (aka “kingpin”) and vertical (90 degrees from the main part of the chassis) when viewed from the side of the car.
On most cars, caster is calculated by adding the kick-up angle of the chassis to any additional caster added by the hub carrier (aka “caster block.”) It can be adjusted either by changing the front bulkhead or adjusting the front-upper suspension mounts.
The kick-up angle is the upward angle of the inside-front of the suspension arm (or suspension pin) when viewed from the side (see diagram above.). 0 degrees kick-up means the arm would be flat. Kick-up and caster have similar effects on handling:
Most on-road cars use 0 degrees of kick-up, or even some negative kick-up (also known as anti-dive.)
More kick-up / caster
- More on-power steering
- More stability
- Better handling in bumps
Less kick-up / caster
- Faster and tighter steering
- Worse handling in bumps
Pro-dive and anti-dive
Some on-road cars use anti-dive which is when the front suspension pins are angled downward at the front, thereby helping to resist the natural tendency of the car's nose to dive when braking. Pro-dive is the same as negative kick-up, and conversely, anti-dive is the same as kick-up.
Some on-road cars have suspension that allows for active caster, that is, caster angles that change as the suspension is compressed.