A frame mechanism for a vehicle with at least three wheels, comprising a vehicle frame assembly, a first wheel frame assembly and a second wheel frame assembly, said second wheel frame assembly including a second wheel frame unit which is connected to said vehicle frame assembly and which is spaced apart from said first wheel frame unit in a front-and-rear direction, and at least one second wheel which is journalled on said second wheel frame unit to cooperate with said first wheels to support said vehicle frame assembly, characterized in that: said first wheel frame assembly includes a first wheel frame unit which has a fork assembly that is connected to said vehicle frame assembly, and a shock absorbing assembly that is connected to said fork assembly; a swing arm which has a swiveling center that is pivotably connected to said shock absorbing assembly such that left and right ends of said swing arm are swingable around said swiveling center and movable together with said shock absorbing assembly in an up-and-down direction; two synchronizing levers which are located at left and right sides of said fork assembly and below said swing arm, each of said synchronizing levers having a pivot end that is journalled on said first wheel frame unit, and a transmitting end that is opposite to said pivot end in the front-and-rear direction; two first wheels, each of which is journalled on said transmitting end of a respective one of said synchronizing levers; and two linking shafts, each of which has an upper pivot end that is pivoted to a respective one of said left and right ends of said swing arm, and a lower pivot end that is pivoted to a respective one of said synchronizing levers so as to transmit movement of said respective synchronizing lever to said swing arm and characterized in that said shock absorbing assembly includes two damping members which are spaced apart from each other, said fork assembly having an extending bridge which interconnects said damping members and on which said swing arm is pivotably mounted, each of said damping members having a cylinder and a piston reciprocally movable in said cylinder and in that said swing arm extends in a left-and-right direction to have said swiveling center pivoted to said extending bridge, and said left and right ends pivotably connected to said upper pivot ends of said linking shafts, respectively. said first wheel frame assembly includes a first wheel frame unit which has a fork assembly that is connected to said vehicle frame assembly, and a shock absorbing assembly that is connected to said fork assembly; a swing arm which has a swiveling center that is pivotably connected to said shock absorbing assembly such that left and right ends of said swing arm are swingable around said swiveling center and movable together with said shock absorbing assembly in an up-and-down direction; two synchronizing levers which are located at left and right sides of said fork assembly and below said swing arm, each of said synchronizing levers having a pivot end that is journalled on said first wheel frame unit, and a transmitting end that is opposite to said pivot end in the front-and-rear direction; two first wheels, each of which is journalled on said transmitting end of a respective one of said synchronizing levers; and two linking shafts, each of which has an upper pivot end that is pivoted to a respective one of said left and right ends of said swing arm, and a lower pivot end that is pivoted to a respective one of said synchronizing levers so as to transmit movement of said respective synchronizing lever to said swing arm and characterized in that said shock absorbing assembly includes two damping members which are spaced apart from each other, said fork assembly having an extending bridge which interconnects said damping members and on which said swing arm is pivotably mounted, each of said damping members having a cylinder and a piston reciprocally movable in said cylinder and in that said swing arm extends in a left-and-right direction to have said swiveling center pivoted to said extending bridge, and said left and right ends pivotably connected to said upper pivot ends of said linking shafts, respectively.