Recently, new type coasters called "robocoasters" that consist with cars of roller coasters and mounted manipulators have been developing mainly in Europe and North America in order to enjoy more thrills. Usual cars of roller coasters that are enjoyed in amusement parks are moved with an initial potential energy from a top of a course. In the coasters, forces that are exerted from the cars to rails are designed and confirmed by experiments when the coasters are set. Then, the forces at any points on rails do not change unless course layouts are changed. However, robocoasters travel with dynamic interactions between cars and mounted manipulators. Thus, forces that are exerted from the cars change with changes of motions of the manipulators, because motions of the seat where passengers ride on, such as motions of the mounted manipulators, influence to motions of cars dynamically. Then, it is considered that exerting influences from cars to rails have to be analyzed dynamically for strength designs of rails. In this paper, a model of a robocoaster is proposed at first. Then, simulations are performed and dynamic effects to the rails caused by changes of motions of the seat are evaluated quantitatively.