Accurate estimation of contact forces is crucial for effective control of quadrupedal robots, especially in complex locomotion scenarios. In this paper, we introduce a novel force estimation technique for robots equipped with transformable leg-wheels. Unlike conventional methods that focus on forces at specific contact points, our approach expresses varying contact points through a simplified kinematic model and derives the corresponding Jacobian matrices. This allows us to apply the virtual work method to evaluate contact forces across the entire surface of the leg-wheel, including the tips, sides, and other contact regions. This adaptability is particularly advantageous in hybrid locomotion modes, where different parts of the leg-wheel interact with the terrain. The proposed method is highly efficient, relying solely on motor current and position feedback without the need for additional sensors. We validate our approach through simulations and real-world experiments, demonstrating its accuracy, robustness, and applicability under diverse operational conditions.