The invention is an adapter chainring for a multiple speed bicycle comprising a derailleur and a crankset having outer and inner chainrings. The adapter chainring has teeth disposed on its outer periphery for engaging the bicycle chain. The adapter chainring defines a plurality of holes which receive bolts to attach the adapter chainring to the crankset in place of the conventional inner chainring of a two chainring crankset, and to a third, smaller inner chainring which is added to the crankset to convert it to a three chainring crankset having additional, lower gears.
A bicycle chainwheel plate is formed to reduce the weight of a chainwheel crank and to keep its stiffness at a high level. The chainwheel plate is coupled between a crank arm and at least one sprocket. In one embodiment, the crank arm is detachable from the chainwheel plate, while in the second embodiment, the crank arm is integrally formed with the chainwheel plate as a one-piece, unitary member. The crank arm is designed to accommodate a pedal at its free end and is centrally attached to the chainwheel plate at the other end. In the first embodiment, the chainwheel plate comprises a crank attachment portion having a centrally located crank attachment hole in which a crank arm can be fixed in a non-rotatable fashion, four connecting arm portions radially extending in four directions from the crank attachment portion, and chainwheel fixing portions bifurcating and extending outward from the tips of the arm portions. The outer sprocket is shaped as a ring and is fixedly coupled to the chainwheel fixing portions.
A bicycle crankset for mounting a plurality of chainrings includes a crank arm having a first end for mounting a pedal and a second end having a boss for mounting to a crank axle, a chainring retainer for supporting at least one of the plurality of chainrings, and a reinforcement member. The chainring retainer has a first engagement member for engaging the boss, and the reinforcement member includes a second engagement member for engaging the boss. The chainring retainer includes a first center ring defining the first engagement member and a plurality of first arms extending radially outwardly from the first center ring. Similarly, the reinforcement member includes a second center ring defining the second engagement member and a plurality of second arms extending radially outwardly from the second center ring. The distal ends of the plurality of first arms may be connected to corresponding distal ends of the plurality of second arms. Alternatively, the chainring retainer may have a first peripheral ring disposed at distal ends of the plurality of first arms, and the reinforcement member may have a second peripheral ring disposed at distal ends of the plurality of second arms. The first peripheral ring may be secured to the second peripheral ring over a part or whole circumference thereof. To provide good balance of the crankset, the plurality of first arms may be offset from the plurality of second arms by a half-pitch in the circumferential direction.
