US20130130852A1

Movatterモバイル変換

Info

Publication number: US20130130852A1
Application number: US13/740,636
Authority: US
Inventors: Maurizio Valle
Original assignee: Campagnolo SRL
Current assignee: Campagnolo SRL
Priority date: 2007-08-09
Filing date: 2013-01-14
Publication date: 2013-05-23
Also published as: ITMI20071660A1; ES2429788T3; US9850992B2; JP2013154881A; US8454461B2; CN104743051B; JP2009107615A; EP2022712A2; TW200911624A; EP2022712B1; CN101362500A; JP6333878B2; JP6188394B2; US20090042680A1; EP2647563A2; RU2008132882A; US20120277046A1; CN104743051A; CN104709432A; US20170190382A1

Abstract

A sprocket assembly mounted to a hub has at least eleven sprockets. The hub is able to rotate about a rotation axis and has a plurality of spoke attachment seats and a fastening portion to a frame of the bicycle. On the hub a predetermined axial distance is defined between a plane, substantially perpendicular to the rotation axis, comprising the points of the spoke attachment seats closest to the freewheel body and a plane, substantially perpendicular to the rotation axis and defined in the fastening portion to the frame, comprising the attachment points to the frame closest to the freewheel body. All of the sprockets of the sprocket assembly, when associated with the freewheel body, have an overall axial width that is lower than or equal to the predetermined axial distance. The chain has a maximum thickness between 4.6 mm and 5.8 mm.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patent application Ser. No. 12/187,560, filed on Aug. 7, 2008, which is incorporated by reference as if fully set forth.

FIELD OF INVENTION

The field of the invention relates to a motion transmission system of a bicycle.

BACKGROUND

In a bicycle transmission system, the combination of a guide toothed wheel with a small diameter with a sprocket with a large diameter allows demanding climbs to be easily handled. However, this same combination, over flat land or going downhill, is disadvantageous since the cyclist's energy is dissipated, due to the fact that the cyclist is obliged to pedal quickly while the bicycle moves forwards slowly.

In order to make the aforementioned combination more suitable for the route to be made, it is known to equip the bicycle with a plurality of guide toothed wheels and with a plurality of sprockets, which can be combined with each other based upon requirements, through appropriate gearshifting devices.

Because bicycle components have reached a high degree of standardization, the characteristic size of components such as frame, gearshifting devices, freewheel body or chain do not greatly vary, so that most bicycles use three guide toothed wheels and up to ten sprockets.

However, certain bicycle transmission systems show a sprocket assembly comprising more sprockets, the largest of which are arranged partially over the spokes of the wheel of the bicycle. The sprockets have a minimum thickness, in the area of engagement with the chain, equal to 1.76 mm, whereas the distance between adjacent sprockets is lower than the minimum thickness of the sprockets themselves, and in particular is equal to 1.66 mm. In order to be made to rotate, the sprocket assembly illustrated requires the use of a special-shaped chain. The aforementioned chain comprises, in alternating succession, a first link, consisting of two plates that are parallel and spaced apart to define the area of engagement with a tooth of a sprocket, and a second link, consisting of a single plate shaped like a “bridge” so as to define in a central portion thereof a seat for coupling with the next tooth of the sprocket.

The aforementioned chain, thanks to the second link made with a single plate, has a maximum thickness much smaller than a conventional chain and for this reason it can also be used when there is a space between the sprockets that is smaller than the thickness of the sprockets themselves.

The aforementioned chain wears down quickly because of the continuous friction between the teeth of the sprockets and the second links consisting of a single shaped plate. This makes it subject to premature structural yielding.

Further, in such an arrangement, the sprockets that are arranged over the spokes of the wheel have a large diameter, i.e. they have a very high number of teeth. Since the number of teeth of the smallest sprocket of known sprocket assemblies is now standardized and goes up to about 11-12 teeth, it follows that passing from the smallest sprockets to the largest ones there is a non-linear increase in diameters, and therefore in the number of teeth. In other words, the cyclist notices a great difference in effort necessary to pedaling from one sprocket to an adjacent sprocket that has a great difference in teeth compared to the previous one. Therefore, it is possible that the cyclist is not able to find the optimum combination of sprockets and guide toothed wheels even with such a large number of sprockets.

In addition to the above, the total bulk of the sprocket assembly is very high at the bicycle wheel, for which reason the chain, when engaging the end sprockets, is inclined with respect to the guide toothed wheels and therefore more subject to friction, wear and tension peaks.

Throughout the present description and in the subsequent claims, the expression “motion transmission system” in a bicycle is used to indicate the assembly of at least some of the components active in the transmission of motion, imparted by the cyclist through pedaling, from the crank arms to the rear wheel of the bicycle.

The present invention relates, in a first aspect thereof, to a motion transmission system of a bicycle, comprising a sprocket assembly adapted to be mounted on a freewheel body of a hub of a bicycle rear wheel and a bicycle chain adapted to engage the sprockets of the sprocket assembly, the sprocket assembly comprising at least eleven sprockets, the hub being able to rotate about a rotation axis and comprising a plurality of attachment seats of the spokes of the rear wheel of the bicycle and a fastening portion to a frame of the bicycle, a predetermined axial distance being defined on the hub between a plane, substantially perpendicular to the rotation axis, comprising the points of the spoke attachment seats closest to the freewheel body and a plane, substantially perpendicular to the rotation axis and defined in the fastening portion to the frame, comprising the attachment points to the frame closest to the freewheel body, wherein all of the sprockets of the sprocket assembly, when they are associated with the freewheel body, have an overall axial width or bulk smaller than, or equal to, the predetermined axial distance, and in that the chain has a maximum thickness in the direction of the rotation axis comprised between 4.6 mm and 5.8 mm, the extreme values being included.

BRIEF DESCRIPTION OF THE DRAWING(S)

Certain characteristics and advantages shall become clearer from the following detailed description of a preferred embodiment thereof, made with reference to the attached drawings and given for indicating and not limiting purposes. In such drawings:

FIG. 1 schematically shows a side view of a bicycle comprising a motion transmission system;

FIG. 2 schematically shows a longitudinal section view of a portion of the motion transmission system ofFIG. 1, i.e. of a sprocket assembly mounted on a freewheel body of a hub of a bicycle rear wheel, such a sprocket assembly being engaged with a bicycle chain;

FIG. 3 schematically shows a plan view from above of the sprocket assembly ofFIG. 2 mounted in a bicycle frame;

FIG. 4 schematically shows a plan view from above of a complete transmission system according to the present invention mounted on a bicycle frame,FIG. 3 being an enlarged detail of thisFIG. 4;

FIGS. 5 and 6 schematically show a plan view from above and, respectively, a top side view of the chain ofFIG. 2;

FIG. 7 schematically shows a longitudinal section view of a portion of the chain ofFIGS. 5 and 6, taken according to the plane traced with the line VII-VII ofFIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Introduction

The present invention relates, in a first aspect thereof, to a motion transmission system of a bicycle, comprising a sprocket assembly adapted to be mounted on a freewheel body of a hub of a bicycle rear wheel and a bicycle chain adapted to engage the sprockets of the sprocket assembly, the sprocket assembly comprising at least eleven sprockets, the hub being able to rotate about a rotation axis and comprising a plurality of attachment seats of the spokes of the rear wheel of the bicycle and a fastening portion to a frame of the bicycle, a predetermined axial distance being defined on the hub between a plane, substantially perpendicular to the rotation axis, comprising the points of the spoke attachment seats closest to the freewheel body and a plane, substantially perpendicular to the rotation axis and defined in the fastening portion to the frame, comprising the attachment points to the frame closest to the freewheel body, wherein all of the sprockets of the sprocket assembly, when they are associated with the freewheel body, have an overall axial bulk smaller than, or equal to, the predetermined axial distance, and in that the chain has a maximum thickness in the direction of the rotation axis comprised between 4.6 mm and 5.8 mm, the extreme values being included.

The use of a sprocket assembly having the aforementioned axial bulk and of a chain having the aforementioned thickness allows, on the one hand, a high strength of the transmission system with at least eleven sprockets to be ensured, at the same time allowing conventionally-shaped chain and sprockets to be used, to the advantage of the simplicity of construction and reliability of the transmission system. In particular, the chain is smaller in size than the chains currently used for sprocket assemblies with ten sprockets, so as to allow narrower sprockets and/or smaller distances between conventional sprockets to be used, which results in a lightweight assembly.

More specifically, although the maximum thickness of the chain is less than that currently used for a chain of a sprocket assembly with ten sprockets, the aforementioned thickness of the chain ensures a surprisingly high strength, and in particular it is possible to use a conventionally-shaped chain, which is sufficiently strong, contrary to certain prior art that suggests using a specially-shaped chain. In addition thereto, conventional chains, thanks to the presence of a bush able to rotate freely in the link engaged by a tooth, ensure that the friction between the tooth and the chain does not limit the smooth running of the transmission system.

Moreover, the transmission system described herein provided for the use of a sprocket assembly in which no sprocket is intended to be arranged over the spokes of the wheel of the bicycle, for which reason the sprockets added after the tenth one can advantageously be intermediate sprockets, and not end sprockets with a large diameter as required in the prior art. This enormously increases the linearity of the increase in diameter of the sprockets, since it is possible for example to have a greater number of adjacent sprockets with a difference in teeth equal to just one tooth.

Moreover, the use of a sprocket assembly having an axial bulk such as to be able to be entirely housed on the freewheel body of the hub without being arranged over the spokes of the wheel allows such a sprocket assembly to be suitably positioned, for which reason it can be ensured that the chain, when engaging the end sprockets, is not excessively inclined, thus limiting its wear and the generation of tension peaks.

The chain may comprise an alternating succession of outer links and inner links, connected each other at respective connection ends, each link, outer and inner, comprising two respective plates, outer and inner, being arranged parallel and spaced apart to define a space for receiving a tooth of a sprocket. The shape of the chain of the transmission system may be conventional, which contributes to the simplicity and cost-effectiveness of manufacturing the transmission system.

The maximum thickness may be between 4.8 mm and 5.6 mm, the extreme values being included. Preferably, the maximum thickness is comprised between 5 mm and 5.5 mm, the extreme values being included. These aforementioned maximum thicknesses of the chain ensure a sufficiently high reliability.

Preferably, the axial width or bulk is lower than or equal to 46 mm, and more preferably lower than or equal to 43.5 mm.

In this way, the aforementioned sprocket assembly can be housed in a conventional bicycle having wheels and frame of standardized size.

The distance between two end sprockets of the sprocket assembly, measured between respective faces of the end sprockets facing outwardly from the sprocket assembly, may be lower than or equal to 42.5 mm, and preferably lower than or equal to 40.5 mm.

In this way the chain can engage the sprocket with the smallest diameter with sufficient margin as not to slide in the frame of the bicycle, and the gearshift can position the chain on the sprocket with the largest diameter without interfering with the spokes of the wheel.

The sprockets may have a predetermined position and are spaced apart.

In another embodiment of the transmission system, the sprocket with the smallest diameter of the sprocket assembly has 11 or 12 teeth and the sprocket with the largest diameter has a number of teeth comprised between 23 and 27.

The transmission system has a sprocket assembly comprising a combination of eleven sprockets selected from the following:

- a first combination with sprockets having 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 23 teeth respectively;
- a second combination with sprockets having 11, 12, 13, 14, 15, 16, 17, 19, 21, 23, 25 teeth respectively;
- a third combination with sprockets having 11, 12, 13, 14, 15, 17, 19, 21, 23, 25, 27 teeth respectively;
- a fourth combination with sprockets having 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 25 teeth respectively;
- a fifth combination with sprockets having 12, 13, 14, 15, 16, 17, 19, 21, 23, 25, 27 teeth respectively.

In another alternative, the transmission system has a sprocket assembly comprising a combination of twelve sprockets selected from the following:

- a first combination with sprockets having 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23 teeth respectively;
- a second combination with sprockets having 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 25 teeth respectively;
- a third combination with sprockets having 11, 12, 13, 14, 15, 17, 18, 19, 21, 23, 25, 27 teeth respectively;
- a fourth combination with sprockets having 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 25 teeth respectively;
- a fifth combination with sprockets having 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 25, 27 teeth respectively.

The sprockets may have a maximum thickness, at an engagement area with the chain, lower than or equal to 1.7 mm, and more preferably lower than or equal to 1.6 mm.

The distance between at least two consecutive sprockets of the sprocket assembly, measured between the engagement area with the chain of the sprocket with the smallest diameter and an adjacent sprocket, is greater than or equal to the thickness of the sprockets. Moreover, the distance between all of the consecutive sprockets of the sprocket assembly may be greater than or equal to the thickness of the sprockets.

The distance between consecutive sprockets may be lower than or equal to 2.2 mm.

This makes it possible to use a chain with plates of the links having relatively large thicknesses and thus being sufficiently strong.

The sprockets with a smaller diameter may be placed at greater distances apart than the sprockets with a larger diameter. Further, the sprockets with a smaller diameter may be at a distance apart lower than or equal to 2.5 mm.

Such distances between sprockets allow the passage of a conventionally-shaped chain with particularly strong sections.

At least six consecutive sprockets may have a number of teeth that differs by one from that of at least one adjacent sprocket. Moreover, one of the at least six sprockets has eighteen teeth.

Moreover, the consecutive sprockets may be at least seven in number. Even further, the consecutive sprockets may have at least eight or at least nine in number.

In this way, in the movement of the chain from one sprocket to another the cyclist does not notice a great difference in effort.

The transmission system may comprise at least one guide toothed wheel associated with at least one crank arm and adapted to be engaged by the chain at the same time as one of the sprockets of the sprocket assembly. The at least one toothed wheel may be made from aluminum alloy and has a maximum thickness, in the engagement area of the chain, lower than or equal to 1.7 mm. Further, the maximum thickness of the at least one toothed wheel and of the sprockets, in the respective engagement areas of the chain, is the same. In particular, the maximum thickness may be lower than or equal to 1.6 mm in combination with a chain having a thickness lower than or equal to 5.5 mm.

Thanks to the dimensions indicated above it is possible to make toothed wheels that are light and sufficiently strong.

In a second aspect thereof, the sprocket assembly for a bicycle rear wheel comprises at least eleven sprockets, wherein all of the sprockets of the sprocket assembly have an overall axial width or bulk lower than or equal to 46 mm.

Such a sprocket assembly may have, individually or in combination, all of the structural and functional characteristics discussed above with reference to the sprocket assembly of the motion transmission system and therefore has all of the aforementioned advantages.

In particular, the axial bulk of the sprocket assembly is preferably lower than or equal to 43.5 mm.

The distance between two end sprockets of the sprocket assembly, may be measured between respective faces of the end sprockets facing outwardly from the sprocket assembly, is lower than or equal to 42.5 mm, and more preferably lower than or equal to 40.5 mm.

The sprockets may have a predetermined position and are spaced apart.

In another embodiment of the sprocket assembly, the sprocket with the smallest diameter has 11 or 12 teeth and the sprocket with the largest diameter has a number of teeth comprised between 23 and 27.

The aforementioned sprocket assembly may comprise a combination of eleven sprockets selected from the following:

In another alternative, the sprocket assembly may comprise a combination of twelve sprockets selected from the following:

The sprockets may have a maximum thickness, at an engagement area with a bicycle chain, lower than or equal to 1.7 mm, and more preferably lower than or equal to 1.6 mm.

The distance between at least two consecutive sprockets of the sprocket assembly, measured between the engagement area with a bicycle chain of the sprocket with the smallest diameter and an adjacent sprocket, may be greater than or equal to the thickness of the sprockets.

Moreover, the distance between all of the consecutive sprockets of the sprocket assembly may be greater than or equal to the thickness of the sprockets.

Preferably, the distance between consecutive sprockets is lower than or equal to 2.2 mm.

In another embodiment of the sprocket assembly, the sprockets with a smaller diameter may be placed at greater distances apart than the sprockets with a larger diameter. The sprockets with a smaller diameter may be at a distance apart lower than or equal to 2.5 mm.

At least six consecutive sprockets may have a number of teeth that differs by one from that of at least one adjacent sprocket. Moreover, one of the at least six sprockets preferably has eighteen teeth.

Further, the consecutive sprockets may be at least seven in number. Even further, the consecutive sprockets may be at least eight or at least nine in number.

In a third aspect thereof, the bicycle chain comprises an alternating succession of outer links and inner links, connected each other at respective connection ends, each link, outer and inner, comprising two respective plates, outer and inner, arranged parallel and spaced apart to define a space for receiving a tooth of a sprocket of a sprocket assembly of a bicycle rear wheel, wherein it has a maximum thickness comprised between 4.6 mm and 5.8 mm, the extreme values being included.

Such a bicycle chain has, individually or in combination, all of the structural and functional characteristics discussed above with reference to the chain of the motion transmission system and therefore has all of the aforementioned advantages.

In particular, the maximum thickness is between 4.8 mm and 5.6 mm, the extreme values being included, and more preferably between 5 mm and 5.5 mm, the extreme values being included.

In a fourth aspect thereof, a bicycle comprises a transmission system, and/or a sprocket assembly and/or a chain of the type described above.

Such a bicycle may have, individually or in combination, all of the structural and functional characteristics discussed above with reference to the aforementioned transmission system and/or sprocket assembly and/or chain.

In a fifth aspect thereof, a bicycle comprises a sprocket assembly having at least eleven sprockets, wherein the sprocket assembly is positioned so that the difference between the distance of the sprocket with the smallest diameter from a chain line of the bicycle and the distance of the sprocket with the largest diameter from the chain line is lower than or equal, in absolute value, to 4 mm.

In such a bicycle, when the chain is in the engagement positions of the end sprockets, it is not excessively inclined and it is not subject to wear and tension peaks.

The distance of the sprocket with the smallest diameter from the chain line is equal to the distance of the sprocket with the largest diameter from the chain line.

DESCRIPTION

With initial reference toFIG. 1, abicycle51 is shown to which a motion transmission system in accordance with the present invention is applied, wholly indicated with59.

Thebicycle51 ofFIG. 1 comprises aframe53 to which afront wheel55 and arear driving wheel57 are connected.

What makes thefront wheel55 different from therear driving wheel57 is that the second receives the motion from thetransmission system59 of thebicycle51. This system comprises a pair of crankarms50 directly coupled with one or more guidetoothed wheels12. The crankarms50 are supported in rotation in theframe53 through abottom bracket assembly14 comprising a shaft and some bearings. The guide toothedwheels12 engage achain15 to transmit the torque applied by the cyclist on the crankarms50 to asprocket assembly16 coupled with therear driving wheel57.

In particular, therear driving wheel57 comprises arim58, somespokes18 and ahub20. Thehub20 is per se known and for this reason is only schematically illustrated: it comprises a first body56 (FIG. 3) coupled with therim58 through thespokes18 and a second body that rotates as a unit with thesprocket assembly16. The second body is indicated withreference numeral22 inFIG. 2 and is known as freewheel body since it is free to rotate with respect to thefirst body56 in a direction of rotation, and move it into rotation in the opposite direction. The rotation axis is indicated with X inFIG. 2.

On thefirst body56 of thehub20 there are seats54 (FIG. 3) for the attachment of thespokes18 to thehub20. On the axially opposite side to the seats54, thehub20 comprises aportion540 for attachment to theframe53 of thebicycle51.

Thesprocket assembly16 comprises a plurality of driven toothed wheels, known as sprockets, having a different outer diameter to one another: in the example illustrated inFIGS. 2-4, there are eleven sprockets and they are indicated with reference numerals1 to11, from the sprocket1 having the largest outer diameter to thesprocket11 having the smallest outer diameter.

Agearshifting device24, illustrated inFIG. 1, allows thechain15 to be moved from an engagement condition with a sprocket to an engagement condition with another sprocket. A similar device can also be provided in the area of thecrank arms50 in the case in which there is more than oneguide toothed wheel12. In this way the sprockets and the toothed wheels can be associated with each other through thechain15 in a plurality of combinations.

With reference toFIGS. 2 and 3, thesprocket assembly16 has a size such as to be able to be entirely housed in the space of thehub20 between theportion540 for attachment to theframe53 of thebicycle51 and the portion ofbody56 where the seats54 are made. In particular, thesprocket assembly16 is of a size such as to be able to be housed in the space E between the planes Z and Y, where Z is the plane, perpendicular to the axis X of thehub20, passing through the points of the seats54 closest to thefreewheel body22, and Y is the plane, perpendicular to the axis X and defined in the portion for attachment to theframe53 of the hub, passing through the points of thehub20 where the attachment to theframe53 takes place and that are closest to thefreewheel body22.

In particular, the portion of theframe53 to which the wheel is fastened in general is shaped like a fork with a face facing towards thesprocket assembly16, indicated withreference numeral159 inFIGS. 2 and 3 and the points of thehub20 where the attachment to theframe53 takes place and that are closest to thefreewheel body22 are defined at a plane defined on theface159.

The space E has a predetermined axial distance greater than or equal to 46 mm and thesprocket assembly16 has an axial bulk lower than or equal to 46 mm, preferably lower than or equal to 43.50 mm. Further, the sprocket with thesmallest diameter11 has a distance F from theface159 of theframe53 at least equal to 2 mm or such that when thechain15 engages it the distance G of thechain15 from theframe53 is at least equal to 0.5 mm.

Moreover, the distance M between the faces1aand11aof thesprockets1 and11 facing towards the outside of thesprocket assembly16 is lower than or equal to 42.5 mm, and preferably lower than or equal to 40.5 mm, compared with an engagement area of the sprockets made on thefreewheel body22 with a length N lower than or equal to 39 mm.

With reference toFIG. 3 it can be seen that thanks to the size of thesprocket assembly16 it can be positioned substantially symmetrically with respect to the chain line LC of thebicycle51, conventionally defined by the standardization rules at a predetermined distance W from the middle plane MD of the bicycle51 (in the case of use of a pair of guide toothed wheels associated with the crank arms, the chain line is arranged substantially at half the distance between the two guide toothed wheels). This means that the face1aof the sprocket1 with the largest diameter and the face11aof thesprocket11 with the smallest diameter have respective distances DS′ and DS″ from the chain line LC that are substantially equal or with a difference lower than 4 mm.

This means that when thechain15 is engaged respectively with the sprocket1 with the largest diameter and with thesprocket11 with the smallest diameter it is inclined with respect to the chain line LC by substantially equal acute angles α′ and α″, as shown inFIG. 4. Preferably, the angles α′ and α″ are between 2.25° and 3.75°.

Thesprocket assembly16 meets the measurements indicated above since the sprockets from1 to11 have a thickness O substantially constant along a radial direction, and lower than or equal to 1.7 mm and, moreover, the distance P between most of the adjacent sprockets is greater than the thickness of the sprockets but lower than or equal to 2.3 mm.

Actually, the thickness of the sprockets could also be variable along a radial direction, but what's more is that in the engagement area with thechain15 sprockets from1 to11 have a maximum thickness lower than or equal to 1.7 mm and preferably lower than or equal to 1.6 mm.

Preferably, moreover, all of the sprockets are placed at a distance P apart lower than or equal to 2.2 mm.

Alternatively, some sprockets are at a distance apart greater than 2.2 mm. According to the preferred embodiment shown inFIG. 2, the

sprockets

9,10 and11 are at distances apart P′ and P″ equal to 2.4 and 2.5 mm.

Thechain15 is illustrated in detail inFIGS. 5 to 7 and has a conventional shape. It comprises an alternating succession ofouter links60 andinner links61, connected each other at respective connection ends60aand61a.

Each outer link comprises twoouter plates15aand eachinner link61 comprises twoinner plates15b. The plates of each link are arranged parallel and spaced apart to define a space for receiving a tooth of a sprocket. Theouter plates15aare farther apart than theinner plates15band they partially overlap them at the respective connection end60aand61a. Arivet15crotatably joins theinner plates15bto theouter plates15aat the respective connection ends60aand61a.

In particular, the ends60aof theouter plates60 haverespective holes60band theends61aof theinner plates61 have respective holes61b, theholes60band61bhaving substantially the same diameter and being aligned to house therivets15c. Around therivet15c, between the twoinner plates15b, there is abush15dcapable of rotating freely about the axis of the rivet (FIG. 7). Between therivet15cand thebush15d

flanged portions

61cof theinner plates15bare arranged, located around the holes61band extending towards the inside of thelink61.

The maximum thickness R of thechain15 is lower than or equal to 5.8 mm and preferably lower than or equal to 5.5 mm.

In any case, the chain has a minimum thickness greater than or equal to 4.6 mm, preferably greater than or equal to 4.8 mm and even more preferably greater than or equal to 5 mm. These values ensure sufficient structural strength to satisfy the current technical standards. In the case in which the guidetoothed wheels12 associated with the crankarms50 are made from aluminum alloy, at least in the part intended to engage thechain15, the latter preferably has a thickness comprised between 5 and 5.7 mm.

With the sizes indicated above, some combinations of eleven sprockets that can be housed substantially in the space in which the combinations of ten sprockets of the prior art are housed, are the following:

- first combination with sprockets having 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 23 teeth respectively;
- second combination with sprockets having 11, 12, 13, 14, 15, 16, 17, 19, 21, 23, 25 teeth respectively;
- third combination with sprockets having 11, 12, 13, 14, 15, 17, 19, 21, 23, 25, 27 teeth respectively;
- fourth combination with sprockets having 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 25 teeth respectively;
- fifth combination with sprockets having 12, 13, 14, 15, 16, 17, 19, 21, 23, 25, 27 teeth respectively.

Some combinations with twelve sprockets are the following:

- first combination with sprockets having 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23 teeth respectively;
- second combination with sprockets having 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 25 teeth respectively;
- third combination with sprockets having 11, 12, 13, 14, 15, 17, 18, 19, 21, 23, 25, 27 teeth respectively;
- fourth combination with sprockets having 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 25 teeth respectively;
- fifth combination with sprockets having 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 25, 27 teeth respectively.

Of course, a person of ordinary skill in the art can bring numerous modifications and variants to the motion transmission system of a bicycle described above, in order to satisfy contingent and specific requirements, all of which are anyway covered by the scope of protection as defined by the following claims.