Truck and Trailer

Hey all, in my current game, a top down car game using physics, I'd like to have a big semi truck with a trailer. I have it so that the trailer's phy_position_x and y are equal to the truck's every step and the phy_rotation is equal to the trucks. I would like the phy_rotation to not be exactly the same however, making the trailer seem like its turning slower than the cab would be a cool effect. Any help on how to do this would be cool :)