Rim definition1. On a bicycle , the metal or wooden hoop of a wheel that holds the tire and tube and the outer ends of the spokes .
2. On a truck, the metal assembly consisting of a base and either a side ring or a side and lock ring combination, which are removable from one side for tire mounting. The opposite side has a fixed flange to retain the tire. Note: Passenger and tubeless rims do not have removable side and lock rings. Also see drop center rim and safety rim .