Abstract: An improved bicycle drive assembly characterized by an elongated, rotary drive shaft, a front gear assembly coupling the forward end of the drive shaft to the bicycle's crank-and-pedal assembly, a disk gear provided with a plurality of radial grooves on its outer face, a torque-shift gear assembly slidingly engaged to the drive shaft and keyed for mutual rotation therewith, and an adjustable spring assembly for biasing the torque-shift gear assembly towards the center of the disk gear. As the torque on the drive shaft is increased the torque-shift gear assembly is forced laterally out across the face of the disk gear to cause a down-shift in gear ratios. As the torque on the drive shaft decreases the spring assembly forces the torque-shift gear back towards the center of the disk gear to up-shift the gearing ratio.