Wireless sensor networks (WSNs) create a new frontier in collecting and processing data from remote locations. The IEEE 802.15.4 wireless personal area network-low rate (WPAN-LR) WSNs rely on hardware simplicity to make sensor field deployments both affordable and long-lasting without maintenance support. WSN designers strive to extend network lifetimes while meeting application-specific throughput and latency requirements. Effective power management places sensor nodes (or motes) into one of the available energy-saving modes based upon the sleep period duration and the current state of the radio. The newest generation of WPAN-LR-based sensor platform radios operates at a 250 kbps data rate and does not provide adequate time to completely power off the radio between the 128-byte constrained IEEE 802.15.4 transmissions. A new radio power management (RPM) algorithm presented in this paper exploits additional energy-saving opportunities introduced with the new generation of faster platform transceivers. The RPM algorithm optimizes radio sleep capabilities by transitioning nodes to intermediate power level states. Additionally, this experimental mote research also provides characterizations for the radio power levels, the mote platform state transition times, and the state transition energy costs of an IEEE 802.15.4 compliant sensor platform for improved accuracy in simulating WSN energy consumption.