Rear bicycle wheel

Abstract

A rear bicycle wheel comprising a rim (20), a hub (24) carrying at least one sprocket (26), and a plurality of spokes (28a, 28b) which connect the hub (24) to the rim (20), in which one first set of spokes (28a) is anchored on one side of the hub adjacent to said sprocket (26), and one second set of spokes (28b) is anchored to one side of the hub further away from said sprocket (26), in which the spokes of the first set (28a) are greater in number than the spokes of the second set (28b).

Description

[0001] The present invention relates to a rear bicycle wheel.

[0002] FIG. 1 of the annexed drawings illustrates a rear wheel of a known type mounted on the frame of a bicycle 10 having two fork-shaped arms 12 provided at their bottom ends with seats, designated generically by 14, for fixing of a pin defining an axis 16 of transverse rotation. The rear wheel, designated as a whole by 18, comprises a rim 20 having a median plane 22 set in a central position with respect to the arms 12 and the seats 14 for attachment of the frame 10. The wheel 18 comprises a hub 24 that carries a set of sprockets 26 set coaxially with the hub 24. The rim 20 and the hub 24 are connected together by means of one first set of spokes and one second set of spokes, designated, respectively, by 28a and 28b. The spokes 28a of the first set are anchored along one side of the hub 24 adjacent to the sprocket set 26, whilst the spokes 28b of the second set are anchored to the hub 24 on the side of the latter further away from the sprocket set 26.

[0003] On account of the encumbrance of the sprocket set 26 in the direction of the transverse axis 16, the spokes 28a, 28b have a different inclination with respect to the median plane 22 of the wheel 18. In FIG. 1, the angles of inclination of the spokes 28a and 28b with respect to the median plane 22 are designated, respectively, by α and β. The difference between the angles α and β is greater, the greater is the axial encumbrance of the sprocket set 26.

[0004] In traditional solutions, the fact that the spokes 28a and 28b have a different inclination with respect to the median plane 22 means that the said spokes are subjected to different tensioning forces. In particular, the tensioning force of the spokes 28a will have to be considerably higher than the tensioning force of the spokes 28b in order to keep the rim 20 centred with respect to the median plane 22 of the wheel. If the mean tensioning forces of the spokes 28a and 28b are respectively designated by Fa and Fb, in order to have correct centring of the rim 20 with respect to the median plane 22, the components of these forces in the direction parallel to the axis of rotation of the wheel must be equal and opposite to one another.

[0005] The main drawback of the known solution previously described lies in the fact that the spokes of the wheel that are adjacent to the sprocket set undergo a very high tensioning force and are much more subject to the risk of failure as compared to the spokes located on the side of the wheel opposite to the sprocket set.

[0006] The purpose of the present invention is to provide a rear bicycle wheel that is free from the aforementioned drawback.

[0007] In accordance with the present invention, the above purpose is achieved by a bicycle wheel having the characteristics that form the subject of the main claim.

[0008] The characteristics and advantages of the present invention will emerge clearly from the ensuing detailed description, which is provided purely by way of nonlimiting example, with reference to the attached drawings, in which:

[0009] FIG. 1, already described previously, is a partial axial section of a rear wheel mounted on the frame of a bicycle;

[0010] FIG. 2 is a perspective view of an embodiment of a wheel according to the invention; and

[0011] FIG. 3 is a partial perspective view of the wheel according to the invention.

[0012] In FIGS. 2 and 3 the items corresponding to the ones previously described are designated by the same reference numbers.

[0013] In the wheel 18 according to the present invention the spokes 28a of the first set are greater in number than the spokes 28b of the second set. In the embodiment illustrated in the figures, the spokes 28a are twice as many as the spokes 28b of the second set. Preferably, the spokes 28a and 28b are grouped together in a plurality of sets of three spokes 30 set at equal distances apart. Each set of three spokes 30 comprises two spokes of the first set 28a and one spoke of the second set 28b, the latter being in a central position between the respective two spokes of the first set 28a. The two spokes 28a of each set of three spokes 30 are preferably parallel to one another, and the spoke 28b of the same set of three spokes 30 is contained in a radial plane equidistant from the spokes 28a. The ways in which the spokes 28a, 28b are fixed to the hub 24 and to the rim 20 may be of any type whatsoever.

[0014] As may be seen in FIG. 2, the wheel 18 assumes, from the aesthetic point of view, the configuration of a “spoked” wheel, in which, in actual fact, each spoke is made up of a set of three spokes 30. The number of sets of three spokes 30 may be varied with respect to the embodiment illustrated in FIG. 2. For example, wheels may be built having 5, 6, 7, 8, 9, or 10 “spokes”, i.e., sets of three spokes, having, respectively 15, 18, 21, 24, 27, and 30 spokes in all.

[0015] The solution according to the present invention substantially enables the tensioning force of the spokes 28a to be halved with respect to that of the spokes of the second set 28b, with a consequent considerable reduction in the risk of failure of the spokes adjacent to the sprockets, which, in traditional solutions, are more subject to failure.

[0016] Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may be varied widely with respect to what is described and illustrated herein purely by way of example, without thereby departing from the scope of the present invention as defined in the ensuing claims.

Claims

1. A rear bicycle wheel comprising a rim, a hub carrying at least one sprocket, and a plurality of spokes which connect the hub to the rim, in which one first set of spokes is anchored on one side of the hub adjacent to said sprocket, and one second set of spokes is anchored to one side of the hub further away from said sprocket, the spokes of the first set being greater in number than the spokes of the second set.

2. A wheel according to claim 1, wherein the spokes of the first set are twice as many as the spokes of the second set.

3. A wheel according to claim 2, wherein the spokes are grouped in sets of three spokes set at equal distances apart, each set of three spokes comprising two spokes of the first set and one spoke of the second set.

4. A wheel according to claim 3, wherein the spokes of the first set of each set of three spokes are substantially parallel to one another.

5. A wheel according to claim 4, wherein the spoke of the second set of each set of three spokes is contained in a radial plane set in a central position with respect to the spokes of the first set of the same set of three spokes.