On an unbanked circular turn, the friction force provides the necessary centripetal force. I just want to know how is this friction force originated to produce the necessary friction force. Friction is a reaction force, so what is that force thats radially outward to generate the friction between the tyres and the road. Such as on a banked turn the mgsina is pulling the body along the inclined plane and hence friction is produced to oppose the motion. I just want to know what is the force responsible for the production of friction force necessary for centripetal force on a circular banked turn?