How To Calculate “Reaction Load”
According to Newton's third law, for every action force there is an equal (in size) and opposite (in direction) reaction force or reaction load. Forces always come in pairs - known as "action-reaction force pairs." Identifying and describing action-reaction force pairs is a simple matter of identifying the two interacting objects.
In a Cantilever Gate the two objects are the support rollers. To figure reaction load or force on the rollers see the below diagram: