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We have developed a personal mobility vehicle (PMV) with four driven wheels that is capable of negotiating obstacles with a leg motion mechanism. When obstacles are encountered, wheels are lifted, moved ahead in a stepping-like motion, and lowered back down, thereby allowing the PMV to advance further. In our previous paper, we discussed the principle of the gait algorithm used by our PMV, in which wheels are utilized as legs to negotiate obstacles. In the original algorithm, when the wheels encountered terrain that might require leg motion to traverse, the system determined whether such motion was applicable and, if it was, orchestrated a series of leg motions. However, there were terrains that could not be negotiated using the original algorithm. In this paper, we propose an improved gait algorithm, in which when the vehicle encounters terrain intractable by leg motion with its current posture, the vehicle changes its posture until it can traverse that terrain. We verified the effectiveness of the improved gait algorithm through a variety of mobility tests with a passenger. In addition, we present numerical data on the range of terrain topologies that could be negotiated by the proposed algorithm.