Variable speed traction systems require constant adaptation of torque and speed, and thus, it is desirable to reduce motor size and weight by approximating constant power curve as much as possible. The design strategies under which a permanent magnet motor can demonstrate significant torque over-boost and field weakening capabilities using single-gear transmission are investigated. This paper gives a good quantitative comparison of surface-mounted, internal, and hybrid rotor topologies, featuring permanent magnets by introducing a power utilization coefficient, which benchmarks the capability of a traction system to utilize its rated power over the whole speed range, while optimal transmission ratio is investigated for the three rotor topologies.