Abstract: An improvement of multi-stage sprocket assembly for bicycle includes at least a small sprocket and a large sprocket. The large sprocket includes at least two different sets of teeth. The large sprocket defines a radial second center line across the thickness thereof while the first set of teeth each defines a first center line across the teeth crest and parallel to the second center line. The first center line is moved away from the second center line in an opposite direction of the small sprocket. The second set of teeth includes at least two consecutive special teeth. The first special tooth has a recess formed under the root in a lateral side facing the small sprocket to avoid interference with the chain during shifting movement. The second special tooth has its first center line moving away from the second center line of the large sprocket toward the small sprocket for engaging with the chain at a small rotation angle without raising the chain or changing the tension of the chain during shifting movement.

Abstract: Disclosed is an improvement on bicycle freewheel gear cluster gear-shifting mechanism having at least at least a large-diameter sprocket wheel, an intermediate-diameter sprocket wheel. The improvement includes a plurality of protrusions provided on the rim of the large-diameter sprocket wheel on the side facing the intermediate-diameter sprocket wheel. The plurality of protrusions can be used to prevent the drive chain from overshooting to the large-diameter sprocket wheel when the drive chain is being shifted from the small-diameter sprocket wheel to the intermediate-diameter sprocket wheel. Additionally, a plurality of protrusions are provided on the rim of the large-diameter sprocket wheel near the gear-up assistant hooking members. The plurality of protrusions can be used to prevent the drive chain from being hooked up by the gear-up assistant hooking members when the drive chain is being shifted from the large-diameter sprocket wheel down to the small-diameter sprocket wheel.