Load capacity ratings of the Gate Casters are NOT related to the springs. Load capacity ratings are offered as an idea of what the gate casters will carry without failure. They are NOT absolute, but rather depend on the usage and service.
One side of a gate is usually attached to a column which supports most of the weight of the gate. The purpose of the spring in a gate caster is only to keep the caster wheel touching the floor when the floor is not level. If ithe floor level from the lowest point to the highest point is more that 1″ then the gate caster will not be able to touch the floor at one end, either at the lowest point or at the highest point.
If the gate caster supports the weight when the floor is at the lowest level then the spring is not being used. As the gate goes up the incline the gate caster still supports the weight, but the spring begins to compress. How much the spring compresses depends on the slope of the floor. Spring compression has nothing to do with the weight. It depends on how uneven the floor is. If your slope of travel exceeds 1″ the gate caster will not function properly. If it exceeds 1/2″ the spring may not return to its original shape.