When talking about the big three in a vehicle’s suspension, caster is probably the hardest to visualize and the least mentioned. Camber and toe are much easier to wrap your head around, but it’s important that we understand caster because if we don’t, the customer may notice a diminished lack of handling.

Perhaps caster can best be defined as the steering pivot angle of the front wheels. Because it is not something easily visualized, it can be a difficult concept to grasp. First, let’s dig a little deeper into the meaning of caster.

Caster is either positive or negative. Positive caster occurs when a line drawn perpendicular through the pivot point intersects the ground in front of the tire’s contact patch. Negative caster exists when that line intersects the ground behind the tire’s contact patch.

To help make all of this a bit easier to grasp let’s take a look at caster as it is used on a bicycle.

All bicycles have lots of positive caster. You can assure yourself of this by sighting down the frame tube that holds the fork in place. If you extend an imaginary line from that tube to the ground you find that it intersects the ground well ahead of the tire’s contact patch.

The importance of all of this is that the longitudinal forces acting on the tire’s contact patch are behind the footprint and, therefore, make the bicycle want to move forward in a straight line.

Now imagine grabbing hold of t...

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