This paper presents a comprehensive wheel model that can quantitatively evaluate traction performance of flexible/rigid wheelsdriving on deformable terrain. The proposed model exploits a terramechanics-based approach with taking account of pressures generated by wheel elasticity as well as terrain stiffness. Deflection of a flexible wheel typically depends on a relative pressure between thewheel and terrain: the wheel will be significantly deformed on rigid terrain whereas it will be hardly deformed on soft terrain. Therefore, the wheel-terrain interaction in the proposed model is divided into three contact sections: wheel front section, wheel deflected(flat) section, and wheel rear section. The traction force of the wheel is obtained as an integral of normal and shear stresses generatedat each section. Simulation studies with varied wheel pressures, such as flexible, semi-flexible, and rigid wheels, are conducted tovalidate the proposed model. Also, traction performances of flexible/rigid wheels are compared based on a metric called tractiveefficiency. The comparison implies an optimal wheel pressure of flexible wheel for better traction performance.