JP2023032952A - rear sprocket - Google Patents

Abstract

To provide a rear sprocket in which the radial height of sprocket teeth is set so that chain jumping hardly occurs.SOLUTION: A rear sprocket, which is mountable to a rear hub assembly for a human powered vehicle and has a pitch circle with respect to a pitch circle diameter, includes a sprocket body and a plurality of sprocket teeth that extend radially outward from the outer periphery of the sprocket body in a radial direction with respect to the center axis of rotation of the rear sprocket. The plurality of sprocket teeth include a plurality of low radial-height teeth each having a radially outermost tooth tip about the center axis of rotation. The maximum low tooth tip distance is defined as the distance from the center axis of rotation to the radially outermost tooth tip in the radial direction. The maximum low tooth tip distance is less than the half of the pitch circle diameter, and the total number of the plurality of low radial-height teeth is 50 percent or more of the total number of the plurality of sprocket teeth.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to rear sprockets.

For example, the bicycle rear sprocket disclosed in Patent Literature 1 has two types of teeth with different widths in the rotation center axis direction.

JP-A-2002-137785

In the sprocket teeth of the bicycle rear sprocket disclosed in Patent Document 1, the radial height from the rotation center axis of the bicycle rear sprocket to the radially outermost tooth tip of the sprocket tooth is defined. Conventionally, the radial height of most sprocket teeth is designed to be greater than half the pitch diameter of a rear bicycle sprocket. However, if the bicycle rear sprocket is a small diameter sprocket with a total number of sprocket teeth of 12 or less, and the radial height of most of the sprocket teeth is greater than half the pitch circle diameter of the bicycle rear sprocket, the following will occur. problems can arise. That is, the bicycle chain is not sufficiently engaged with the sprocket teeth, and the tension acting on the bicycle chain during driving disengages the bicycle chain from the engaged sprocket teeth, causing the bicycle rear sprocket to rotate downstream in the driving rotational direction. A phenomenon could occur in which the bicycle chain engages another sprocket tooth located on the side. Hereinafter, this phenomenon will be referred to as chain jump in this specification.

One object of the present disclosure is to provide a rear sprocket in which the radial height of the sprocket teeth is set so that chain jumping is less likely to occur.

A rear sprocket according to a first aspect of the present disclosure is attachable to a rear hub assembly for a human powered vehicle and has a pitch circle with respect to a pitch circle diameter, the rear sprocket comprising: a sprocket body; a plurality of sprocket teeth extending radially outward in a radial direction with respect to the center axis of rotation of the rear sprocket, wherein each of the plurality of sprocket teeth has a plurality of small diameter radially outermost tooth tips with respect to the center axis of rotation. Including directional height teeth, wherein a maximum low tip distance is defined as the distance from the center axis of rotation to the radial outermost tooth tip in the radial direction, and the maximum low tip distance is the pitch circle diameter Less than half, the total number of said plurality of low radial height teeth is 50 percent or more of the total number of said plurality of sprocket teeth.
According to the rear sprocket on the first side, 50% or more of the sprocket teeth are low radial height teeth with low height, so even if the rear sprocket has a small diameter, the drive chain is sufficiently engaged with the sprocket teeth. match. Therefore, chain jumping is less likely to occur.

In the second side rear sprocket according to the first aspect of the present disclosure, the total number of said plurality of low radial height teeth is 70 percent or more of the total number of said plurality of sprocket teeth.
According to the rear sprocket on the second side, 70% or more of the sprocket teeth are low radial height teeth, so even if the rear sprocket has a small diameter, the drive chain is sufficiently engaged with the sprocket teeth. match. Therefore, chain jumping is less likely to occur.

In the third aspect rear sprocket according to the first or second aspect of the present disclosure, the total number of said plurality of low radial height teeth is equal to or greater than 80 percent of the total number of said plurality of sprocket teeth.
According to the rear sprocket on the third side, 80% or more of the sprocket teeth are low radial height teeth, so even if the rear sprocket has a small diameter, the drive chain is sufficiently engaged with the sprocket teeth. match. Therefore, chain jumping is less likely to occur.

In the fourth side rear sprocket according to the first to third aspects of the present disclosure, the total number of said plurality of low radial height teeth is less than 100 percent of the total number of said plurality of sprocket teeth.
According to the fourth side rear sprocket, the plurality of sprocket teeth includes sprocket teeth that are not short sprocket teeth. Therefore, the drive chain is more likely to move to an adjacent sprocket by contacting a sprocket tooth that is not a short sprocket tooth. Therefore, smooth shift operation is possible.

In the fifth aspect rear sprocket according to the fourth aspect of the present disclosure, the total number of said plurality of low radial height teeth is no more than 90 percent of the total number of said plurality of sprocket teeth.
According to the fifth aspect rear sprocket, the plurality of sprocket teeth includes sprocket teeth that are not short sprocket teeth. Therefore, the drive chain is more likely to move to an adjacent sprocket by contacting a sprocket tooth that is not a short sprocket tooth. Therefore, smooth shift operation is possible.

In the sixth aspect rear sprocket according to the first to fifth aspects of the present disclosure, the plurality of sprocket teeth have a maximum high tip distance that is greater than the maximum low tip distance of the plurality of low radial height teeth. at least one higher radial height tooth with.
The sixth side rear sprocket facilitates movement of the drive chain to an adjacent sprocket by contacting at least one high radial height tooth. Therefore, smooth shift operation is possible.

In the rear sprocket of the seventh aspect according to the sixth aspect of the present disclosure, the maximum high tip distance of the at least one high radial height tooth is greater than half the pitch circle diameter.
According to the rear sprocket on the seventh side surface, since the high radial direction teeth are high, the drive chain can easily move to the adjacent sprocket by coming into contact with the high radial direction teeth. Therefore, smooth shift operation is possible.

In the eighth aspect rear sprocket according to the sixth or seventh aspect of the present disclosure, the at least one higher radial height tooth has a chamfered tip configured to facilitate upshifting. In the upshift operation, the drive chain shifts from the rear sprocket to an adjacent small sprocket adjacent to the rear sprocket in a state where there is no other sprocket between the rear sprocket and the rear sprocket in the axial direction about the rotation center axis. be done.
According to the eighth side rear sprocket, the drive chain is guided toward the adjacent small sprocket by the chamfered tooth tips of the high radial direction height teeth. Therefore, the upshift operation in which the drive chain moves from the rear sprocket to the adjacent small sprocket is smoothly performed.

In the rear sprocket of the ninth aspect according to the eighth aspect of the present disclosure, the chamfered addendum of the at least one high radial height tooth has a diameter between the chamfered addendum and the rotation center axis. The directional distance tapers toward the adjacent small sprocket such that the directional distance decreases in the direction from the rear sprocket to the adjacent small sprocket.
According to the ninth side rear sprocket, the drive chain is guided toward the adjacent small sprocket by the chamfered tooth tips of the high radial direction height teeth. Therefore, the upshift operation in which the drive chain moves from the rear sprocket to the adjacent small sprocket is smoothly performed.

The rear sprocket of the tenth aspect according to the first through ninth aspects of the present disclosure, wherein the pitch circle is defined by a plurality of virtual chain rollers, each of the plurality of virtual chain rollers each having a plurality of drives of the plurality of sprocket teeth. Each of the plurality of virtual chain rollers has one of the plurality of roller central axes in contact with one of the surfaces and such that the pitch circle passes through all of the plurality of roller central axes.
According to the rear sprocket on the tenth side surface, since the height of the lower radial height teeth is sufficiently low, the drive chain is sufficiently engaged with the sprocket teeth even if the diameter of the rear sprocket is small. Therefore, chain jumping is less likely to occur.

In the rear sprocket of the eleventh aspect according to the tenth aspect of the present disclosure, the pitch polygon is defined by linearly connecting the plurality of roller center axes, and the radial outermost tooth tip is defined with respect to the rotation center axis , located radially outward from the pitch polygon.
According to the eleventh side rear sprocket, the low radial height teeth have the necessary radial height to drive the drive chain. Therefore, necessary drive performance is ensured.

In the twelfth aspect of the rear sprocket according to the first to eleventh aspects of the present disclosure, the total number of the plurality of sprocket teeth is 12 or less.
According to the rear sprocket on the twelfth side, chain jumping is less likely to occur even with a small-diameter sprocket having a total number of sprocket teeth of 12 or less.

According to the rear sprocket of the present disclosure, it is possible to provide a rear sprocket in which the radial height of the sprocket teeth is set so as to prevent chain jumping.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows a part of human-powered vehicle provided with the rear sprocket of embodiment. The side view of the rear sprocket with which the manpowered vehicle of FIG. 1 is provided. FIG. 3 is a perspective view of the rear sprocket of FIG. 2; FIG. 3 is a side view showing the rear sprocket of FIG. 2 and a virtual chain roller contacting the rear sprocket; FIG. 5 is a partial enlarged view showing low radial height teeth of the rear sprocket of FIG. 4; FIG. 5 is a partially enlarged view showing high radial direction height teeth of the rear sprocket of FIG. 4 ; FIG. 3 is a front view of lower radial height teeth of the rear sprocket of FIG. 2; FIG. 3 is a front view of high radial height teeth of the rear sprocket of FIG. 2 ; FIG. 3 is a plan view of the lower radial height teeth of the rear sprocket of FIG. 2; FIG. 3 is a plan view of high radial height teeth of the rear sprocket of FIG. 2 ; FIG. 3 is a side view showing the rear sprocket and drive chain of FIG. 2;

<First embodiment>
A rear sprocket for a human-powered vehicle according to an embodiment will be described with reference to FIGS. 1 to 11 . The manpowered vehicle 10 shown in FIG. 1 is a vehicle that has at least one wheel and can be driven by at least manpower. The human powered vehicle 10 includes various types of bicycles, such as mountain bikes, road bikes, city bikes, cargo bikes, hand bikes, and recumbent bikes. The number of wheels that the manpowered vehicle 10 has is not limited. Manpowered vehicles 10 also include, for example, one-wheeled vehicles and vehicles having three or more wheels. The manpowered vehicle 10 is not limited to vehicles that can be driven solely by manpower. The human-powered vehicle 10 includes an E-bike that uses not only the human-powered driving force but also the driving force of an electric motor for propulsion. E-bikes include electrically assisted bicycles whose propulsion is assisted by an electric motor. Hereinafter, in the embodiments, the manpowered vehicle 10 will be described as a bicycle.

As used herein, the following directional terms "front", "rear", "forward", "backward", "left", "right", "lateral", "upward", and , “downward”, and any other similar directional terms refer to those directions determined with reference to the rider facing the handlebars in a reference position (e.g., on the saddle or seat) of the manpowered vehicle 10. Point.

As shown in FIG. 1 , manpowered vehicle 10 includes crank 12 , front sprocket 14 , rear hub assembly 16 , multiple rear sprockets 20 , and drive chain 60 . A rear sprocket 20 is attachable to a rear hub assembly 16 for a human powered vehicle 10 .

As shown in FIG. 1 , the drive chain 60 is wound around the front sprocket 14 and one rear sprocket 20 selected from a plurality of rear sprockets 20 .

As shown in FIGS. 2 to 6, the rear sprocket 20 includes a sprocket body 22 and a plurality of sprocket teeth extending radially outward from the outer periphery of the sprocket body 22 in a radial direction RD with respect to the rotation center axis CA of the rear sprocket 20. 24 and.

The plurality of sprocket teeth 24 includes a plurality of low radial height teeth 28 each having a radially outermost tooth tip 26 about the center axis of rotation CA. The rear sprocket 20 shown in FIGS. 2-6 has twelve sprocket teeth 24 including ten low radial height teeth 28 .

Each sprocket tooth 24 has two axial side surfaces 30 and 32 that intersect the rotation center axis CA, a drive surface 34 that transmits driving force to and from the drive chain 60, and a drive surface 34 that extends in the circumferential direction of the rear sprocket 20. and a non-driving surface 36 opposite the . The two axial sides 30, 32 include an outer side 30 facing the outside of the manpowered vehicle 10 and an inner side 32 facing the inside of the manpowered vehicle 10 in an axial direction AD with respect to the center axis of rotation CA. The driving surface 34 is located upstream of the non-driving surface 36 in the driving rotation direction DR of the rear sprocket 20 .

As shown in FIGS. 4-6, the rear sprocket 20 has a pitch circle PC with respect to the pitch circle diameter PCD. A pitch circle PC is defined by a plurality of virtual chain rollers VCR. Each of the plurality of virtual chain rollers VCR has one of the plurality of roller central axes RCA. Each of the plurality of virtual chain rollers VCR contacts one of the plurality of drive surfaces 34 of the plurality of sprocket teeth 24, and the pitch circle PC passes through all of the plurality of roller center axes RCA. The virtual chain roller VCR shown in FIGS. 4-6 is a phantom representation of the chain roller 62 of the drive chain 60 shown in FIG.

A maximum low addendum distance MLD is defined as the distance from the center axis of rotation CA to the radially outermost addendum 26 of the low radial height tooth 28 in the radial direction RD. The maximum low addendum distance MLD is less than half the pitch circle diameter PCD. The maximum low addendum distance MLD may be slightly less than half the pitch circle diameter PCD.

A pitch polygon PP is defined by linearly connecting multiple roller center axes RCA of multiple virtual chain rollers VCR. The radially outermost tooth addendum 26 is arranged radially outward from the pitch polygon PP with respect to the rotation center axis CA. The radially outermost tooth tip 26 may be substantially parallel to a straight line connecting the roller central axes RCA located on both sides of the radially outermost tooth tip 26 in the circumferential direction. The radial outermost tooth addendum 26 may extend in an arc shape along the pitch circle PC. Preferably, the radially outermost tooth tip 26 of the low radial height tooth 28 is arranged radially inside the pitch circle PC and radially outside the pitch polygon PP with respect to the rotation center axis CA.

As shown in FIGS. 5, 7 and 9, the outer side surface 30 and the inner side surface 32 of the low radial height tooth 28 are chamfers that taper toward each other toward the radially outermost tooth tip 26. It has a portion 48 . As a result, the tip portions of the low radial height teeth 28 are tapered so that the drive chain 60 can easily engage the low radial height teeth 28 .

The total number of low radial height teeth 28 is 50 percent or more of the total number of sprocket teeth 24 . The total number of low radial height teeth 28 may be 70 percent or more of the total number of sprocket teeth 24 . The total number of low radial height teeth 28 may be 80 percent or more of the total number of sprocket teeth 24 . The total number of low radial height teeth 28 may be less than 100 percent of the total number of sprocket teeth 24 . The total number of low radial height teeth 28 may be 90 percent or less of the total number of sprocket teeth 24 . The total number of sprocket teeth 24 may be twelve or less.

For example, if the manpowered vehicle 10 includes multiple rear sprockets 20 , the ratio of the total number of low radial height teeth 28 to the total number of sprocket teeth 24 may vary for each rear sprocket 20 .

As shown in FIGS. 2-6 , the plurality of sprocket teeth 24 has at least one high tooth height having a maximum high tooth top distance MHD that is greater than the maximum low tooth height distance MLD of the plurality of low radial height teeth 28 . It includes radial height teeth 38 . The maximum high addendum distance MHD of at least one high radial height tooth 38 is greater than half the pitch circle diameter PCD. The maximum high addendum distance MHD is defined as the distance from the rotation center axis CA to the radially outermost addendum 40 of the high radial height tooth 38 in the radial direction RD. The rear sprocket 20 shown in FIGS. 2-6 has two high radial height teeth 38 next to each other.

6, 8, 10 and 11, at least one high radial height tooth 38 has a chamfered tip 42 configured to facilitate upshifting. have. In the upshift operation, the drive chain 60 is directed from the rear sprocket 20 to the adjacent small sprocket 50 adjacent to the rear sprocket 20 in the axial direction AD with respect to the rotation center axis CA in a state where there is no other sprocket between the rear sprocket 20 and the rear sprocket 20. shifted. In upshifting operation, the rear derailleur shifts the drive chain 60 from the rear sprocket 20 toward the adjacent small sprocket 50 . Upshifting is also called outward shifting.

The high radial height tooth 38 has a triangular beveled surface 46 provided between the outer side surface 30 , the non-drive surface 36 and the tooth crest surface 44 . The portion of the high radial height tooth 38 that includes the ramp 46 forms the chamfered tip 42 . Of the chamfered tooth addendum 42 , the radially outermost tooth addendum 40 is located on the outermost side in the radial direction RD. The thickness of the chamfered tip 42 may be smallest at the radially outermost tip 40 .

The chamfered addendum 42 of the at least one high radial height tooth 38 is such that the radial RD distance between the chamfered addendum 42 and the center axis of rotation CA is from the rear sprocket 20 to the adjacent small sprocket 50. It tapers toward the adjacent small sprockets 50 so as to decrease in the heading direction. In other words, the inclined surface 46 moves toward the adjacent small sprocket 50 so that the distance in the radial direction RD between the inclined surface 46 and the rotation center axis CA decreases in the direction from the rear sprocket 20 toward the adjacent small sprocket 50 . incline. In upshifting operation, the drive chain 60 disengages from the high radial height tooth 38 and is guided by the ramp 46 toward the adjacent small sprocket 50 .

The high radial height tooth 38 may have a shape with a pointed tip. Specifically, the tooth top surface 44 of the high radial direction height tooth 38 may be inclined with respect to a straight line connecting the roller central axes RCA located on both circumferential sides of the high radial direction height tooth 38 . A distance in the radial direction RD between the tooth crest 44 and the rotation center axis CA may increase in the drive rotation direction DR. The chamfered addendum 42 may be chamfered so as to slope toward the adjacent small sprocket 50 over substantially the entire thickness of the chamfered addendum 42 . The chamfered tooth tip 42 may be chamfered so that the distance in the radial direction RD between the chamfered tooth tip 42 and the rotation center axis CA decreases as it approaches the non-drive surface 36 .

The action of the rear sprocket 20 in this embodiment will be described.
As shown in FIG. 11, the drive chain 60 is wound around the rear sprocket 20. As shown in FIG. In order for the rear sprocket 20 to be driven by the drive chain 60, the sprocket teeth 24 need to protrude radially outward from at least the pitch polygon PP with respect to the rotation center axis CA. On the other hand, especially when the rear sprocket 20 is a small-diameter sprocket, if the sprocket teeth 24 protrude too far radially outward with respect to the rotation center axis CA, the chain rollers 62 of the drive chain 60 will be tightly interposed between the adjacent sprocket teeth 24. It will not fit and will continue to contact the drive surface 34 of the sprocket tooth 24 at a position radially outside of its intended position. If this state continues, the position at which the chain roller 62 engages with the sprocket teeth 24 is further displaced radially outward and eventually disengages from the sprocket teeth 24, resulting in so-called chain jumping.

As shown in FIGS. 4 to 6 , in the rear sprocket 20 according to the present embodiment, the maximum distance RD in the radial direction from the rotation center axis CA to the radial outermost tooth tip 26 of the low radial height tooth 28 is The low addendum distance MLD is less than half the pitch circle diameter PCD. On the other hand, the radially outermost tooth tip 26 of the low radial height tooth 28 is arranged radially outward from the pitch polygon PP with respect to the rotation center axis CA. Therefore, the rear sprocket 20 according to the present embodiment ensures sufficient performance for being driven by the drive chain 60, while making it difficult for the chain to jump.

As shown in FIGS. 4 to 10 , the rear sprocket 20 in this embodiment has high radial height teeth 38 . The high radial height tooth 38 has a chamfered tip 42 . The chamfered addendum 42 is preferably arranged such that the distance in the radial direction RD between the chamfered addendum 42 and the rotation center axis CA decreases in the direction from the rear sprocket 20 toward the adjacent small sprocket 50. It slopes toward the adjacent small sprocket 50.

In FIG. 11, when the rider performs an upshift operation via the shift operating device, the drive chain 60 moves from the rear sprocket 20 to the adjacent small sprocket 50 adjacent to the rear sprocket 20 in the axial direction AD with respect to the rotation center axis CA. is shifted to At this time, when the drive chain 60 comes into contact with the chamfered addendum 42 of the high radial height tooth 38 , the drive chain 60 is guided along the inclination of the chamfered addendum 42 toward the adjacent small sprocket 50 . to move smoothly. Therefore, the rear sprocket 20 facilitates the upshift operation of the manpowered vehicle 10 .

In this embodiment, a pair of high radial height teeth 38 are adjacent to each other. Therefore, during an upshift operation, the inner link plate of the drive chain 60 always comes into contact with the chamfered tooth tip 42 of one of the high radial direction height teeth 38, so that the drive chain 60 is adjacent to the drive chain 60. It is quickly shifted to the small sprocket 50.

<Modification>
The descriptions of the embodiments are illustrative of possible forms of rear sprockets according to the present disclosure and are not intended to limit the forms. A rear sprocket according to the present disclosure may take, for example, a modification of the embodiments shown below and a combination of at least two mutually consistent modifications. In the following modified examples, the same reference numerals as in the embodiment are given to the parts that are common to the embodiment, and the description thereof is omitted.

• Only one of the plurality of sprocket teeth 24 may be the high radial height tooth 38 . A plurality of sprocket teeth 24 may include three or more high radial height teeth 38 .

- A plurality of high radial height teeth 38 may be adjacent to each other, and one or more low radial height teeth 28 may be arranged between the high radial height teeth 38 .

The smallest rear sprocket, which is the outermost rear sprocket 20 in the axial direction AD with respect to the rotation center axis CA, may not have the high radial height teeth 38 for facilitating the upshift operation. In this case, the total number of low radial height teeth 28 of the smallest rear sprocket 20 is 100 percent of the total number of sprocket teeth 24, and the number of low radial height teeth 28 of the other rear sprockets 20 is 100 percent of the total number of sprocket teeth 24. The total number may be less than 100 percent of the total number of sprocket teeth 24 .

- One or more of the rear sprockets 20 of the plurality of rear sprockets 20 may have low radial height teeth 28 .

As used herein, the phrase "at least one" means "one or more" of the desired option. As an example, the phrase "at least one" as used herein means "only one option" or "both of the two options" if the number of options is two. As another example, the expression "at least one" used herein means "only one option" or "any combination of two or more options" if the number of options is three or more. means.

AD... axial direction, CA... rotation center axis, MHD... maximum high tooth tip distance, MLD... maximum low tooth tip distance, PC... pitch circle, PCD... pitch circle diameter, PP... pitch polygon, RCA... roller central axis, RD...Radial direction, VCR...Virtual chain roller, 10...Manpowered vehicle, 16...Rear hub assembly, 20...Rear sprocket, 22...Sprocket body, 24...Sprocket tooth, 26...Radial outermost tooth tip, 28...Lower diameter Direction height tooth 34 Drive surface 38 High radial height tooth 42 Chamfered tooth tip 50 Adjacent small sprocket 60 Drive chain.

Claims (12)

A rear sprocket mountable to a rear hub assembly for a man-powered vehicle and having a pitch circle related to a pitch diameter, comprising:
sprocket body and
a plurality of sprocket teeth extending radially outward from the outer circumference of the sprocket body in a radial direction with respect to the rotation center axis of the rear sprocket;
the plurality of sprocket teeth including a plurality of low radial height teeth each having a radially outermost tooth tip with respect to the center axis of rotation;
The maximum low tooth tip distance is defined as the distance from the rotation center axis to the radial outermost tooth tip in the radial direction,
the maximum low tooth tip distance is less than half the pitch circle diameter,
The rear sprocket, wherein the total number of said plurality of low radial height teeth is 50 percent or more of the total number of said plurality of sprocket teeth. 2. The rear sprocket of claim 1, wherein the total number of said plurality of low radial height teeth is 70 percent or more of the total number of said plurality of sprocket teeth. 3. The rear sprocket of claim 1 or 2, wherein the total number of said plurality of low radial height teeth is equal to or greater than 80 percent of the total number of said plurality of sprocket teeth. 4. The rear sprocket of any preceding claim, wherein the total number of said plurality of low radial height teeth is less than 100 percent of the total number of said plurality of sprocket teeth. 5. The rear sprocket of claim 4, wherein the total number of said plurality of low radial height teeth is no greater than 90 percent of the total number of said plurality of sprocket teeth. 2. from claim 1, wherein said plurality of sprocket teeth includes at least one high radial height tooth having a maximum high tip distance greater than said maximum low tip distance of said plurality of low radial height teeth. 6. The rear sprocket according to any one of 5. 7. The rear sprocket of claim 6, wherein the maximum high tip distance of the at least one high radial height tooth is greater than half the pitch circle diameter. The at least one high radial height tooth has a chamfered tip configured to facilitate upshifting, in which the drive chain moves from the rear sprocket to the center of rotation. 8. The rear sprocket according to claim 6 or 7, wherein the rear sprocket is shifted to an adjacent small sprocket adjacent to the rear sprocket with no other sprocket between the rear sprocket in the axial direction with respect to the axis. The chamfered addendum of the at least one high radial height tooth is such that the radial distance between the chamfered addendum and the center axis of rotation is from the rear sprocket to the adjacent small sprocket. 9. The rear sprocket of claim 8, sloping toward said adjacent small sprocket so as to decrease in direction. The pitch circle is defined by a plurality of virtual chain rollers,
the plurality of virtual chain rollers such that each of the plurality of virtual chain rollers contacts one of the plurality of drive surfaces of the plurality of sprocket teeth and the pitch circle passes through all of the plurality of roller central axes; 10. A rear sprocket according to any preceding claim, wherein each roller has one of said plurality of roller central axes. a pitch polygon defined by linearly connecting the plurality of roller central axes;
11. The rear sprocket according to claim 10, wherein said radially outermost tooth addendum is arranged radially outward from said pitch polygon with respect to said rotation center axis. 12. The rear sprocket of any preceding claim, wherein the plurality of sprocket teeth has a total number of twelve or less.

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