Camber is the angle between the vertical axis of the wheel and road surface. Camber can be positive and negative.
(a) Positive Camber – Top of the tires begin to tilt outwards, away from the axle.
(b) Negative Camber – Top of the tires tilts inwards, i.e. towards the axle.
Negative camber is advantageous in case of gripping during heavy cornering. Generally cars are provided with a small amount of negative camber so as to increase contact surface area. Over a period of time, vehicles might tend to gain positive camber. To avoid this also, a small amount of negative camber in provided.
Caster is the forward or backward tilting of the steering axis with respect to the vertical axis of a wheel. It too can be +ve or –ve.
(a) Positive Caster – Backward tilt is considered positive caster.
(b) Negative Caster – Forward tilt is considered os negative caster
When a vehicle has positive caster, a line drawn through the steering axis centerline meets the road surface, ahead of the centerline of the wheel. Conversely for negative caster. Positive caster makes the vehicle more stable at high speeds, and makes straight ahead acceleration easier with minimal driving effort. However as positive caster increases effort needed to turn the steering wheel also increases.
Vehicles with negative caster, on the other hand tend to lose stability.