It is illustrated that a bicycle can be modeled as a multibody system with nonholonomic constraints together with numerical simulations. First, we demonstrate kinematical relations due to a spatial kinematical loop in a bicycle and nonholonomic constraints of the non-slipping condition between tires and a ground can be systematically represented by dual connection matrices. Then, we derive required equations of motion of an illustrative bicycle by using the Lagrange-d' Alembert principle. Finally, we illustrate some numerical simulations of direct dynamics using the mathematical model of the bicycle in order to show the validity of the proposed model.