by 
The Curious Bag
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Caster angle is one of those terms that sounds like black magic to the layman, but the principle is actually very simple. This setting is critical to defining a vehicle's handling, ride and braking characteristics.
Caster
Caster angle is defined as the direction that the suspension travels vertically relative to the ground.
Caster Angle
If a vehicle's suspension moves perfectly up and down, it is said to have zero caster. If the wheel moves up and back under compression, the caster is negative.
Negative Caster Drawbacks
Since much of the vehicle's weight is transferred to the front suspension under braking, excessive negative (backward leaning) caster can cause the vehicle to nosedive.
Negative Caster Advantages
If the wheel is allowed to move up and backward under compression, the vehicle can more smoothly absorb road imperfections. This is utilized to great extent by luxury cars, which is why older Cadillacs often nosedive under braking.
Positive Caster Drawbacks
If the caster is set to lean forward instead of back, the suspension will not be able to absorb large road imperfections like potholes.
Positive Caster Benefits
Forward-leaning suspensions can yield improvements in braking, high speed stability and steering feel.
Source:
Resource:
Steering Geometry on a Handcycle (Video)
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