WO2019027875A1 - Chainring - Google Patents

Abstract

A chainring that provides variable mechanical advantage and gear torque multiplication includes a first peripheral region and a second peripheral region which are offset in opposite directions from a top dead center point. The chainring radius to the second peripheral region is less than the radius to the first peripheral region. Embodiments of the chainring connect to a crank assembly so that the first peripheral region engages the chain during the power phase of a first crank arm rotation and the second peripheral region engages the chain during the power phase of a second crank arm rotation. These features provide increased mechanical advantage during the power phase of the second crank arm rotation compared to the first crank arm, enabling a rider to rest one leg while maintaining a high pedaling cadence. Other embodiments are useful as a motorcycle sprocket.

Description

TITLE: CHAINRING

Cross-Reference to Related Application

This application claims priority to United States provisional application number 62/538,917, filed 31 July 2017, which is incorporated by reference as if fully recited herein.

Technical Field

The disclosed embodiments pertain generally to bicycles and other chain driven

transportation, and more specifically to a chainring which provides variable mechanical advantage or gear torque multiplication.

Background of the Art

Riding a bicycle long distances, at speed, against the wind, or climbing up steep, continuous hills is both mentally and physically exhausting. One method to delay fatigue when climbing is to maintain the highest pedaling cadence (i.e. crankarm revolutions per minute) which is both comfortable and sustainable. Non-circular yet symmetric chainrings which provide variable mechanical advantage have been used in efforts to improve cadence or reduce physical wear related to pedaling at high gear ratios. Examples of these devices are disclosed in US Pat. No. 5,549,314 to Sassi; US Pat. No. 7,749,117 to Carrasco Vergara; and US Pat. No. 8,079,288 to Nakatani. There remains a need in the art for a mechanism to provide increased mechanical advantage or gear torque multiplication while enabling a rider to maintain a relatively high cadence and speed.

Summary

Generally speaking, the present disclosure teaches a chainring that provides a lower gear ratio and a greater mechanical advantage during the power stroke phase of a first crank arm as compared to a second crank arm. This enables a bicycle rider to rest a fatigued, weak, or non- dominant leg, while pedaling with a higher cadence than would otherwise be sustainable, which is especially beneficial when cycling uphill.

A chainring generally cooperates with a crank assembly and a chain of a bicycle, the crank assembly having a first crank arm and a second crank arm. In one embodiment, the chainring is configured for connection to the crank assembly, and the chainring has an axis of rotation, an outer periphery, and a top dead center point. The outer periphery includes a first peripheral region having a first region center point located between about 45° and about 135° offset from the top dead center point about the axis of rotation, and having a full angular extent of between about 25° and about 140°. The outer periphery further includes a second peripheral region having a second region center point located between about 45° and about 135° offset from the top dead center point about the axis of rotation and in the opposite direction from the first region center point, and having a full angular extent of between about 25° and about 140°. The radius from the axis of rotation to all points on the second peripheral region is less than the radius from the axis of rotation to all points on the first peripheral region. The first region center point is offset about the axis of rotation from the second region center point by between about 160° and about 180°. The chainring is configured for connection to the crank assembly so that when the first or second crank arm is rotated the first peripheral region engages the chain during the power phase of the first crank arm rotation and the second peripheral region engages the chain during the power phase of the second crank arm rotation. These features combine to provide a greater mechanical advantage and gear torque multiplication during the power phase of the second crank arm rotation than during the power phase of the first crank arm rotation, the second crank arm corresponding to the leg which the rider desires to rest.

In another embodiment, the radius from the axis of rotation to any point on the first peripheral region may be constant. In yet another embodiment, the radius from the axis of rotation to any point on the second peripheral region may be constant. In this manner, the chainring radius within the first or second peripheral regions may correspond to the radius of a standard circular chainring.

In another embodiment, the first peripheral region may have a full angular extent of between about 50° and about 90°. In another embodiment, the second peripheral region may have a full angular extent of between about 90° and about 140°.

In another embodiment, the first peripheral region is connected to the second peripheral region along the outer periphery by a third peripheral region and a substantially opposing fourth peripheral region. The radius from the axis of rotation to all points on the third peripheral region and the fourth peripheral region may be less than the radius from the axis of rotation to all points on the first peripheral region. These features are advantageous because the radius of the chainring is reduced in regions where the force applied to the crank arms is least (such regions are also referred to as dead spots or dead zones of the pedal stroke). In another embodiment, the chainring has a central mechanical axis offset from the axis of rotation, and the chainring is radially symmetric about the central mechanical axis.

In another embodiment, the first region center point may be offset about the axis of rotation from the second region center point by about 180°.

In another embodiment, the radius from the axis of rotation to second region center point is between about 84% to about 97% of the radius from the axis of rotation to the first region center point. In yet another embodiment, the radius from the axis of rotation to second region center point may be between about 88% to about 93% of the radius from the axis of rotation to the first region center point.

In another embodiment, the chainring may be configured for connection to the crank assembly so that when the first or second crank arm is rotated the first peripheral region engages the chain during the power phase of the second crank arm rotation and the second peripheral region engages the chain during the power phase of the first crank arm rotation. This feature enables alternate connection of the chainring so that either leg may correspond to the increased mechanical advantage portion (second peripheral region) of the chainring.

In other embodiments, a crank assembly includes a chainring in accordance with any of the embodiments described above.

In another embodiment, a crank assembly includes a chainring connected to a spider along a common central mechanical axis, the chainring having an outer periphery and a top dead center point. A first crank arm and a second crank arm are connected to the spider along an axis of rotation, the axis of rotation being offset from the central mechanical axis. The chainring outer periphery has a first peripheral region and a second peripheral region. The first peripheral region has a first region center point located between about 45° and about 135° offset from the top dead center point about the axis of rotation, and has a full angular extent of between about 25° and about 140°. The second peripheral region has a second region center point located between about 45° and about 135° offset from the top dead center point about the axis of rotation and in the opposite direction from the first region center point, and has a full angular extent of between about 25° and about 140°. The radius from the axis of rotation to all points on the second peripheral region is less than the radius from the axis of rotation to all points on the first peripheral region, the first region center point is offset about the axis of rotation from the second region center point by between about 160° and about 180°, and when the first or second crank arm is rotated the first peripheral region engages the chain during the power phase of the first crank arm rotation and the second peripheral region engages the chain during the power phase of the second crank arm rotation. In this manner, a standard circular chainring may be connected to a crank assembly to provide a greater mechanical advantage during the power phase of the second crank arm rotation than during the power phase of the first crank arm rotation.

In other embodiments, a bicycle includes a chainring in accordance with any of the embodiments described above.

In other embodiments, a bicycle includes a crank assembly in accordance with any of the embodiments described above.

Other embodiments, in addition to the embodiments enumerated above, will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the chainring.

Brief Description of the Drawings

FIG. 1 is an enlarged right side elevation view of a chainring for a bicycle.

FIG. 2 is a right side elevation view of the chainring with a crank assembly.

FIGS. 3A & 3B are right side elevation views of the chainring compared with the chain pin center circles of a 39 tooth chainring and a 36 tooth chainring, respectively.

FIG. 4 is a reduced view of another embodiment of the chainring.

FIG. 5 is a reduced view of another embodiment of the chainring.

FIG. 6 is a reduced view of another embodiment of the chainring.

FIG. 7 is a reduced view of another embodiment of the chainring.

FIG. 8 is a right side elevation view of the chainring in an alternate orientation with a crank assembly.

FIG. 9 is a view of another embodiment of the chainring.

FIG. 10 is a view of another embodiment of a crank set.

FIG. 11 is a view of another embodiment of the chainring.

FIG. 12 is a view of an embodiment of the chainring for use as a motorcycle sprocket. Detailed Description of the Invention

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present embodiments. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present embodiments. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present embodiments.

Reference throughout this specification to "one embodiment", "an embodiment", "one example" or "an example" means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present embodiments. Thus, appearances of the phrases "in one embodiment", "according to an

embodiment", "in an embodiment", "one example" or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and/or sub-combinations in one or more embodiments or examples.

As used in this application, the terms "about" or "approximately" refer to a range of values within plus or minus 10% of the specified number. As used in this application, the term

"substantially" means that the actual value is within about 10% of the actual desired value of any variable, element, or limit set forth herein.

Referring initially to FIG. 1, there is illustrated a right side elevation view of a chainring for a bicycle, the chainring generally designated as 20. As used herein, the term "chainring" includes drivetrain components which engage a chain or belt, and may be used interchangeably with the terms "chain ring", "chainwheel", or "sprocket". The term "bicycle" includes tandem bicycles and other human-powered vehicles. FIG. 2 is a right side elevation view of chainring 20 connected to a spider 510 of a cooperating crank assembly 500 of a bicycle (not shown). Crank assembly 500 includes a first crank arm 502 and a second crank arm 504, the first crank arm 502 being the right side (drive side) crank arm and the second crank arm 504 being the left side (non-drive side) crank arm in the shown embodiment. In the shown embodiment, chainring 20 is connectable to spider 510 by means of a plurality of bolts (not shown) placed through a plurality of bolt holes 28 in chainring 20; although other means of connection to a spider or crank arm axle may be used and are known in the art. More bolt holes 28 or mounting slots for adjustable positioning may be provided in chainring 20 than are connected to the spider at any one time; in the shown embodiment ten bolt holes are present and five bolt holes are configured for connection to the spider at one time, although this number may be more or fewer.

Referring again to FIG. 1, chainring 20 has an axis of rotation 22 (projecting through the page) and an outer periphery 24, generally indicated by the dashed line. For the shown

configuration, chainring 20 is toothed to engage a bicycle chain 600, partially shown projecting away from the chainring in dot-dash lines. Outer periphery 24 of chainring 20 is taken to be the closed curved shape including the points where the chain pin centers lie when engaged with the teeth of the chainring. Other embodiments of chainring 20 which cooperate with non-chain driven cycles may be readily envisioned, such as a toothed pulley or synchronous sprocket for meshingly engaging with a toothed belt.

The outer periphery of chainring 20 has a top dead center point 26, a first peripheral region 30, and a second peripheral region 40. Top dead center point 26 is the topmost point of the outer periphery when first crank arm 502 is in the twelve o'clock position (as shown in FIG. 2). First peripheral region 30 engages chain 600 during the power phase of the first crank arm rotation, corresponding to a first crank arm position of between about one o'clock and about five o'clock. Second peripheral region 40 engages chain 600 during the power phase of the second crank arm rotation, corresponding to a second crank arm position of between about one o'clock and about five o'clock. All clock positions refer to positions as viewed from the right hand side (drive side) of the crankset, regardless of crank arm being referenced.

The radius of chainring 20 from axis of rotation 22 to all points on second peripheral region

40 is less than the radius from axis of rotation 22 to all points on the first peripheral region 30. This configuration of differing chainring radius coupled with one of the first and second peripheral regions engaging the chain during the power phase of each crank arm results in a mechanical advantage increase and gear torque multiplication for one of the crank arms. This feature enables the rider to maintain a constant pedaling cadence by increasing mechanical advantage for a fatigued, weak, or non-dominant leg.

For example, in the configuration of FIG. 2, a right leg dominant rider will engage first peripheral region 30 of chainring 20 during the power phase of the first crank arm rotation (right leg). In the embodiment of FIGS. 1 & 2, first peripheral region 30 has a constant radius rl equivalent to the radius of a standard 39 tooth chain ring, although chainring 20 has 37 total teeth. The term 'standard chain ring' as used herein refers to a common circular chainring having all teeth at a substantially equal radius from the axis of rotation. The rider will engage second peripheral region 40 during the power phase of the second crank arm rotation (left leg). In the shown embodiment, second peripheral region 40 has a constant radius r2 equivalent to the radius of a standard 36 tooth chain ring. When this chainring is used with typical 175mm length crank arms, the example configuration provides an additional 3.4% increase in mechanical advantage and 7.7% more gear torque multiplication for the left leg power phase portion of the pedal stroke, as compared to the right leg. The chainring has an effective 37 tooth gear range.

FIGS. 3A and 3B show the chainring of FIG. 1 compared with the chain pin center circle of a 39 tooth chainring (602) and a 36 tooth chainring (604), respectively, chain pin center circles 602 & 604 shown in dotted lines. As shown in FIG. 3A, first peripheral region 30 has a constant radius over an angular extent, a, of 60° about axis of rotation 22. First peripheral region 30 has a first region center point 32 which is offset from top dead center point 26 (TDC) about axis of rotation 22 by an angle, γ, of about 80° (see FIG. 1). As shown in FIG. 3B, second peripheral region 40 has a constant radius over an angular extent, β, of 124° about axis of rotation 22. Second peripheral region 40 has a second region center point 42 which is offset from TDC about axis of rotation 22 by an angle, δ, of about 100°. Second region center point 42 is offset from TDC in the opposite direction from first region center point 32. In the shown embodiment, first region center point 32 is offset from second region center point 42 by about 180° (γ + δ). In other embodiments, first region center point 32 is offset from second region center point 42 by between about 160° and about 180°.

FIGS. 4-7 show additional embodiments of chainring 20. In each of the embodiments of

FIGS. 4-7, the radius from the axis of rotation 22 to points on first and second peripheral regions (30, 40) is substantially equal to that of a standard circular chainring, with the radius to the second peripheral region 40 being less than the radius to the first peripheral region 30. In the embodiment of FIG. 4, chainring 20 has the radius of a standard 36 tooth chainring in first peripheral region 30 and the radius of a standard 33 tooth chainring in second peripheral region 40. In the embodiment of FIGS. 5-7, chainring 20 has the radius of a standard 39 tooth chainring in first peripheral region 30 while the radius of second peripheral region 40 is equivalent to that of standard 35 tooth, 34 tooth, and 36 tooth chainrings, respectively.

Other embodiments of chainring 20 may be configured to achieve an equivalent result while providing an overall higher or lower gear ratio. For example, the first peripheral region may have the radius of a standard 53 tooth chainring, while the second peripheral region may have the radius of a standard 51, 49, or 47 tooth chainring. In another example, first peripheral region may have the radius of a standard 34 tooth chainring, while the second peripheral region may have the radius of a standard 33, 32, or 30 tooth chainring.

In other embodiments, the radius to points in the first or second peripheral region may be variable, rather than constant, with the radius to all points in the second peripheral region being less than the radius to all points in the first peripheral region. In embodiments, the radius from the axis of rotation to second region center point is between about 84% to about 97% of the radius from the axis of rotation to the first region center point. In other embodiments, the radius from the axis of rotation to second region center point is between about 88% to about 93% of the radius from the axis of rotation to the first region center point.

In the chainrings of FIGS. 4-7, first peripheral region 30 extends over differing angles, a, of

52°, 26°, 58°, and 90°, respectively. First peripheral region 30 may have other angular extents, to provide the desired mechanical advantage for the power stroke of the first crank arm and to maintain constant tooth spacing around the outer periphery of the chainring. In embodiments, first peripheral region 30 has a full angular extent, a, of between about 25° and about 140°. In further embodiments, first peripheral region 30 has a full angular extent, a, of between about 50° and about 90°.

Similarly, in the chainring of FIGS. 4-7, second peripheral region 40 extends over various angles, β, of 126°, 30°, 139°, and 105°, respectively. Second peripheral region 40 may have other angular extents, to provide the desired mechanical advantage for the power stroke of the second crank arm and to maintain constant tooth spacing around the outer periphery of the chainring. In embodiments, second peripheral region 40 has a full angular extent, β, of between about 25° and about 140°. In further embodiments, second peripheral region 40 has a full angular extent, β, of between about 90° and about 140°.

In another embodiment of the chainring, shown in FIG. 11, the first peripheral region has the radius of a standard 39 tooth chainring, and the second peripheral region has the radius of a standard 36 tooth chainring. Second peripheral region 40 extends over an angle, β, of 130°. This embodiment provides a smooth pedal stoke by maintaining the radius of the second peripheral region within at least a portion of the dead zones of the pedal stroke. For comparison, the chain pin center circle of a 36 tooth chainring (604) is shown in dotted lines, extending more than 180° about the chainring and including all of second peripheral region 40. As in other embodiments, the specific gear ratio and number of teeth can be modified while scaling the outer periphery of the chainring to maintain a consistent profile. Bolt holes 28 of the embodiment are provided as slots, which permit the rider to adjust the positioning of top dead center point 26 to increase comfort for various body types and riding styles.

In any of the embodiments discussed herein, chainring 20 may be configured to connect to the crank assembly in multiple orientations, one orientation providing a lower gear ratio for the left crank arm or rider's left leg and another orientation providing a lower gear ratio for the right crank arm or rider's right leg. FIG. 8 shows the chainring embodiment of FIG. 2 connected to crank assembly 500 in an orientation which provides a lower gear ratio for the rider's right leg. In the orientation of FIG. 8, when the first or second crank arm is rotated in the direction of the arrows, first peripheral region 30 engages the chain during the power phase of the rotation of second crank arm 504, which is the left crank arm in the shown embodiment. Second peripheral region 40 engages the chain during the power phase of the first crank arm 502 rotation, first crank arm 502 being the right crank arm in the shown embodiment.

To enable the alternate orientations of FIGS. 2 & 8, two sets of bolt holes are provided in chainring 20, as indicated by numerals 28a and 28b in FIG. 8. Bolt holes 28b are shown connected to spider 510 in FIG. 8. To change from the orientation of FIG. 8 to that of FIG. 2, chainring 20 is first disconnected from spider 510, rotated approximately 180° around the axis of rotation, and reconnected to spider 510 by bolts (not shown) through bolt holes 28a.

FIG. 12 illustrates an embodiment of the chainring suitable for use as a rear sprocket of a motorcycle, dirt bike, or other vehicle in which a motor drives a chain or toothed belt (front sprocket illustration not shown). For these vehicles, a variable gear ratio has the benefit of increasing the rate of acceleration through additional gear torque multiplication. In the sprocket of FIG. 12, bolt holes 28 are provided for mounting the chainring. Angular extents and locations of the first and second peripheral regions are as described in the FIG. 11 embodiment.

Referring again to FIG. 1, first peripheral region 30 is connected to second peripheral region 40 along outer periphery 24 by a third peripheral region 50 and a substantially opposing fourth peripheral region 60. In the shown embodiment, the radius from axis of rotation 22 to all points on third peripheral region 50 and fourth peripheral region 60 is less than the radius from axis of rotation 22 to all points on first peripheral regional 30. Third and fourth peripheral regions 50, 60 correspond to dead zones of the pedal stroke for both crank arms 502, 504 (see FIG. 8), or a crank arm position generally between either about eleven o'clock and about one o'clock or between about five o'clock and about seven o'clock. This feature may be present in any of the embodiments discussed above, and is advantageous because the radius of the chainring is reduced in regions where the force applied to the crank arms is least.

FIG. 9 shows another embodiment of chainring 20, wherein chainring 20 has an axis of rotation 22 which is offset from a central mechanical axis 23 by an offset distance, Dl . Chainring 20 is substantially radially symmetric about central mechanical axis 23, i.e., chainring 20 is circular. Bolt holes 28 of chainring 20 (five in the shown embodiment) are substantially equally spaced about axis of rotation 22, whereby chainring 20 is connectable to a crank assembly so that first peripheral region 30 has a larger radius from axis of rotation 22 than does second peripheral region 40. While the chainring of FIG. 9 shows a horizontal offset of axes 22 and 23 with respect to TDC, one of ordinary skill will appreciate that this offset may have both horizontal and vertical components. Further, alternate or multiple bolt hole patterns, or other means of attachment to a crankset, may be provided as discussed above to enable alternate orientations of the chainring.

Chainring 20 may be comprised of aluminum, titanium, carbon fiber, or other materials. Left side views of chainring 20 are generally mirror images of the right side views provided herein. The thickness of chainring 20 may be between about 1mm and about 4mm, or another thickness as required to properly engage the other components of the bicycle drive mechanism. Chainring 20 may be manufactured by stamping, forging, computer assisted machining, or other means.

Further provided is a crank assembly including a chainring according to any of the embodiments discussed above. A crank assembly including a plurality of chainrings as discussed above is also provided.

FIG. 10 shows an embodiment of a crank assembly 500 including a standard circular 39 tooth chainring 520 and a modified spider 510 to which chainring 520 is mounted. Chainring 520 and spider 510 are aligned along a central mechanical axis 23. Spider 510 is configured to mount to a crank arm 502 along an axis of rotation 22 which is offset from central mechanical axis 23 by an offset distance, D2. In this manner, one or more standard chainrings 520 may be connected to spider 510 and configured so that when a crank arm is rotated the first peripheral region 30 engages the chain during the power phase of the first crank arm rotation and the second peripheral region 40 engages the chain during the power phase of the second crank arm rotation, and the radius from the axis of rotation to all points on the second peripheral region is less than the radius from the axis of rotation to all points on the first peripheral region.

While FIG. 10 shows a spider mounted with a vertical offset of axes 22 and 23 with the first crank arm positioned 90° from TDC, this offset may have both horizontal and vertical components, or only a horizontal component. Further, other means of attaching a standard chainring to a crankset in a radially offset manner may be provided. By way of example, a chainring configured for direct mounting to an axle (without spider) may have an offset central mounting aperture.

Further provided is a bicycle including a chainring or crank assembly as described in any of the embodiments discussed above.

The embodiments of the chainring described herein are exemplary and numerous modifications, combinations, variations, and rearrangements can be readily envisioned to achieve an equivalent result, all of which are intended to be embraced within the scope of the appended claims. Further, nothing in the above-provided discussions of the chainring should be construed as limiting the invention to a particular embodiment or combination of embodiments. The scope of the invention is defined by the appended claims.

The disclosure of United States provisional application number 62/538,917, which this application claims priority to, incorporates material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the US Patent and Trademark Office patent file or records, for the limited purposes required by law, but otherwise reserves all copyright rights whatsoever.

Claims

CLAIMS What is claimed is:

Claim 1. A chainring comprising:

a non-circular form having an axis of rotation, an outer periphery, and a top dead center point;

a first peripheral region of the outer periphery having a first region center point located between about 45° and about 135° offset from the top dead center point about the axis of rotation, and having a full angular extent of between about 25° and about 140°;

a second peripheral region of the outer periphery having a second region center point located between about 45° and about 135° offset from the top dead center point about the axis of rotation and in the opposite direction from the first region center point, and having a full angular extent of between about 25° and about 140°;

wherein the radius from the axis of rotation to all points on the second peripheral region is less than the radius from the axis of rotation to all points on the first peripheral region; and, wherein the first region center point is offset about the axis of rotation from the second region center point by between about 160° and about 180°.

Claim 2. The chainring of claim 1, wherein the radius from the axis of rotation to any point on the first peripheral region is constant.

Claim 3. The chainring of claim 1 or 2, wherein the radius from the axis of rotation to any point on the second peripheral region is constant.

Claim 4. The chainring of any one of claims 1 to 3, wherein the first peripheral region has a full angular extent of between about 50° and about 90°.

Claim 5. The chainring of any one of claims 1 to 4, wherein the second peripheral region has a full angular extent of between about 90° and about 140°.

Claim 6. The chainring of any one of claims 1 to 5, wherein the first peripheral region is connected to the second peripheral region along the outer periphery by a third peripheral region and a substantially opposing fourth peripheral region, and wherein the radius from the axis of rotation to all points on the third peripheral region and the fourth peripheral region is less than the radius from the axis of rotation to all points on the first peripheral region.

Claim 7. The chainring of claim 1, wherein:

the chainring has a central mechanical axis offset from the axis of rotation; and, the chainring is radially symmetric about the central mechanical axis.

Claim 8. The chainring of any one of claims 1 to 7, wherein the first region center point is offset about the axis of rotation from the second region center point by about 180°.

Claim 9. The chainring of any one of claims 1 to 8, wherein the radius from the axis of rotation to second region center point is between about 84% to about 97% of the radius from the axis of rotation to the first region center point.

Claim 10. The chainring of claim 9, wherein the radius from the axis of rotation to second region center point is between about 88% to about 93% of the radius from the axis of rotation to the first region center point.

Claim 11. The chainring of any one of claims 1 to 10, the chainring configured for cooperation with a crank assembly and a chain of a bicycle, the crank assembly having a first crank arm and a second crank arm, wherein the chainring is configured for connection to the crank assembly so that when the first crank arm or the second crank arm is rotated the first peripheral region engages the chain during the power phase of the first crank arm rotation and the second peripheral region engages the chain during the power phase of the second crank arm rotation.

Claim 12. The chainring of claim 11 wherein the chainring is configured for connection to the crank assembly so that when the first or second crank arm is rotated the first peripheral region engages the chain during the power phase of the second crank arm rotation and the second peripheral region engages the chain during the power phase of the first crank arm rotation.

Claim 13. A crank assembly for a bicycle, the crank assembly including a chainring according to the embodiments of any one of claims 1 to 12.

Claim 14. A crank assembly for a bicycle, the crank assembly comprising:

a chainring connected to a spider along a common central mechanical axis, the chainring having an outer periphery and a top dead center point;

a first crank arm and a second crank arm connected to the spider along an axis of rotation, the axis of rotation offset from the central mechanical axis;

a first peripheral region of the outer periphery of the chainring having a first region center point located between about 45° and about 135° offset from the top dead center point about the axis of rotation, and having a full angular extent of between about 25° and about 140°; a second peripheral region of the outer periphery of the chainring having a second region center point located between about 45° and about 135° offset from the top dead center point about the axis of rotation and in the opposite direction from the first region center point, and having a full angular extent of between about 25° and about 140°;

wherein the radius from the axis of rotation to all points on the second peripheral region is less than the radius from the axis of rotation to all points on the first peripheral region;

wherein the first region center point is offset about the axis of rotation from the second region center point by between about 160° and about 180°; and,

wherein when the first or second crank arm is rotated the first peripheral region engages the chain during the power phase of the first crank arm rotation and the second peripheral region engages the chain during the power phase of the second crank arm rotation.

Claim 15. A bicycle including a chainring according to the embodiments of any one of claims 1 to 12.

Claim 16. A bicycle including a crank assembly according to the embodiments of claim 13 or 14.