CASTER

Caster generates the self-centring effect on the front wheels that ensures they automatically return to the straight-ahead position after steering, to the benefit of directional stability.

The caster angle is calculated by drawing an imaginary vertical line through the centre of the wheel, and bisecting it with the ‘pivot line’ – around which the steering turns – that runs through the centre of the wheel hub’s upper ball joint to the centre of the lower joint. The angle between the two lines is the caster angle. The pivot line’s upper end leans rearwards, and the lower end hits the ground slightly ahead of the tyre’s contact patch.

Caster creates negative camber on the outside wheel during steering, known as dynamic camber. As dynamic camber doesn’t have a detrimental effect on straight-line traction, increasing positive caster isn’t an issue, within reason – large amounts increase steering effort, so powerassisted steering will be needed.