Improved apparatus for changing gear ratio in bicycles, especially in race bicycles

摘要

Apparatus for changing bicycle gear ratios comprising pedals (1) to the shaft (3) of which a group of coaxial overdrive gears is fixed, with at least an overdrive gear (20) of larger diameter and at least an overdrive gear (2) of smaller diameter; a plurality of sprockets (4) of different diameter, pack-like disposed close to each other and mounted on the shaft (40) of the rear wheel; a roller chain for the transmission of motion from one of the overdrive gears (2; 20) to one of the sprockets (4); means for shifting the chain (5) from one to another of said sprockets (4), with a cyclist-operated lever-and-wire driving means; and means for guiding the deviation of the chain (5) from one to the other of the overdrive gears (2; 20) in cooperation with the means for shifting the chain (5) over the sprockets (4) of the rear wheel. The teeth of each overdrive gear exhibiting, in correspondence of a respective sector (M, N), reduced height and thickness with respect to the other teeth. Said sectors (M, N) being angularly offset. Connected between each pair of the overdrive gears are means solid to the larger gear of the pair and fixed thereto to guide the deviation of the chain (5) from the smaller overdrive gear to the larger one. IMAGE