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A bicycle rim made of composite material has structural fibers incorporated in a polymeric material. The rim has at least one circumferential reinforcement element based on unidirectional structural fibers extending at a respective intersection of walls of the rim, the direction of the structural fi

A bicycle rim made of composite material has structural fibers incorporated in a polymeric material. The rim has at least one circumferential reinforcement element based on unidirectional structural fibers extending at a respective intersection of walls of the rim, the direction of the structural fiber being circumferential.

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What is claimed is: 1. A bicycle rim comprising a first, a second, and a third layer of composite material comprising structural fibers incorporated in a polymeric material, the first and second layers run parallel with each other at respective portions thereof to form a first wall of the rim, and

What is claimed is: 1. A bicycle rim comprising a first, a second, and a third layer of composite material comprising structural fibers incorporated in a polymeric material, the first and second layers run parallel with each other at respective portions thereof to form a first wall of the rim, and diverge from each other at respective portions thereof, the second and the third layers run parallel with each other at respective portions thereof to form a second wall of the rim, and diverge from each other at respective portions thereof, and the third and first layers run parallel with each other at respective portions thereof to form a third wall of the rim, and diverge from each other at respective portions thereof, the diverging portions of the first, second and third layers each define a respective boundary of an enclosed space where the first, second, and third walls of the rim meet, the enclosed space enclosing a circumferentially extending reinforcement element of unidirectional structural fibers. 2. The bicycle rim of claim 1 wherein said unidirectional structural fibers of said circumferentially extending reinforcement element are embedded in a gluing substance. 3. The bicycle rim of claim 2 wherein said gluing substance has an elongation at break coefficient higher than that of the polymeric material. 4. The bicycle rim of claim 2 wherein said gluing substance has an intralaminar shear strength higher than that of the polymeric material. 5. The bicycle rim of claim 2 wherein said circumferentially extending reinforcement element is obtained from a band of unidirectional fibers incorporated in a polymeric material spirally wound around an axis parallel to the direction of the structural fibers and coated with a film of binder, subjected to a molding cycle with deformation in the cross-section. 6. The bicycle rim of claim 2 wherein said circumferentially extending reinforcement element is obtained from a band of unidirectional fibers incorporated in a polymeric material spirally wound, together with a film of gluing substance, around an axis parallel to the direction of the unidirectional structural fibers, subjected to a molding cycle with deformation in the cross-section. 7. The bicycle rim of claim 2 wherein said circumferentially extending reinforcement element is obtained from a band of loose unidirectional fibers impregnated with polymeric material, coated with a film of binder, and subjected to a molding cycle with deformation in the cross-section. 8. The bicycle rim of claim 1 wherein the unidirectional structural fibers of said circumferentially extending reinforcement element are incorporated in a polymeric material. 9. The bicycle rim of claim 8 wherein the polymeric material of said circumferentially extending reinforcement element has the same composition as the polymeric material of the bicycle rim. 10. The bicycle rim of claim 1 wherein said circumferentially extending reinforcement is substantially triangular in cross-section. 11. The bicycle rim of claim 1 wherein said circumferentially extending reinforcement element further comprises containment fibers of the unidirectional structural fibers, the containment fibers non-continuously extending on the outer surface of the circumferentially extending reinforcement element. 12. The bicycle rim of claim 11 wherein said containment fibers comprise a plurality of externally helically wound unidirectional structural fibers. 13. The bicycle rim of claim 1 wherein said circumferentially extending reinforcement element comprises at least one portion extending for an arc of a circumference of the bicycle rim. 14. The bicycle rim of claim 13 wherein adjacent ends of said at least one portion are tapered and slightly overlapped. 15. The bicycle rim of claim 13 wherein the circumferentially extending reinforcement element comprises a plurality of portions extending for an arc of circumference of the rim, and ends of one of the portions of said circumferentially extending reinforcement element are arranged circumferentially staggered with respect to ends of a second one of the portions of said circumferentially extending reinforcement element. 16. The bicycle rim of claim 13 wherein said circumferentially extending reinforcement element comprises two portions, each extending for an arc of circumference. 17. The bicycle rim of claim 13 wherein said circumferentially extending reinforcement element comprises four portions, each extending for an arc of circumference. 18. The bicycle rim of claim 1 wherein the first, second and third walls of the rim are respectively an upper bridge wall, a side wall of a body region of the bicycle rim, and a tire coupling wing wall. 19. The bicycle rim of claim 1 wherein the first layer defines an outer surface of a body region of the bicycle rim and wings of the bicycle rim, and the second layer defines an inner surface of a respective substantially closed radially inner circumferential chamber. 20. The bicycle rim of claim 10 further comprising an additional layer of composite material arranged at a spoke attachment zone. 21. The bicycle rim of claim 10 wherein said structural fibers of said ply composite material are woven, with weft and warp directions forming an angle of substantially 45° with the circumferential direction. 22. The bicycle rim of claim 10 wherein said structural fibers of said ply composite material are randomly arranged within said polymeric material. 23. The bicycle rim of claim 1 wherein the first layer defines an outer surface of a body region of the bicycle rim and the wings of the bicycle rim, and the second layer defines an inner surface of a tire coupling channel. 24. The bicycle rim of claim 1 wherein said structural fibers are selected from the group consisting of carbon fibers, glass fibers, boron fibers, aramidic fibers, ceramic fibers and combinations thereof. 25. The bicycle rim of claim 1 wherein said polymeric material is a thermosetting resin. 26. The bicycle rim of claim 1 wherein the reinforcement element is comprised of multiple segments and forms a substantially circular shape. 27. The bicycle rim of claim 26 wherein each of the reinforcement elements comprises multiple segments having ends that overlap with an adjacent segment. 28. The bicycle rim of claim 27 wherein each of the reinforcement elements is substantially parallel to another, and the overlapping ends are offset from one another. 29. A bicycle rim comprising a first, a second, a third, and a fourth layer of composite material comprising structural fibers incorporated in a polymeric material, the first and second layers being joined with each other at a portion that forms a first wall of the rim, the second and the third layers being joined with each other at a portion that forms a second wall of the rim, the third and fourth layers being joined with each other at a portion that forms a third wall of the rim, and the fourth and first layers being joined with each other at a portion that forms a fourth wall of the rim, the first, second, third, and fourth layers defining therebetween a space where the first, second, third, and fourth walls meet, the space enclosing a circumferentially extending reinforcement element of unidirectional structural fibers. 30. The bicycle rim of claim 29, wherein the circumferentially extending reinforcement element is substantially rhomboidal-shaped in cross-section. 31. A bicycle rim comprising: a first layer of composite material comprising structural fibers incorporated in a polymeric material that defines a radially inner surface of a body region and wings of the rim, a third layer of composite material comprising structural fibers incorporated in a polymeric material, that defines an inner surface of a tire coupling channel, and a second layer of composite material comprising structural fibers incorporated in a polymeric material, that defines an inner surface of a substantially closed inner circumferential chamber, wherein the first and second, second and third, and first and third layers run parallel at respective portions thereof, and diverse at respective portions thereof, so as to define at least one space that encloses at least one circumferentially extending reinforcement element of unidirectional structural fibers, the diverging portions of each of the first, second, and third layers defining a respective outer boundary of the space. 32. A bicycle rim comprising: a first layer of structural fibers incorporated in a polymeric material that forms a first exterior wall; a second layer of structural fibers incorporated in a polymeric material that forms an interior chamber and joins with the first layer to form the first exterior wall; a third layer of structural fibers incorporated in a polymeric material that forms a second exterior wall and joins with the first and second layers; the first, second and third layers are joined so that the second layer forms a base extending between the first and third layers; the first and third layers are joined to form connecting walls over the base formed by the second layer with the result that the joined layers each define a respective section of a boundary of a space that encloses a circumferentially extending reinforcement element of unidirectional structural fibers. 33. A composite material bicycle rim comprising: at least three layers of structural fibers incorporated in a polymeric material that define a plurality of walls and at least one intersections among at least three walls of the plurality of walls, wherein each of the layers defines a respective side bounding a circumferential space at the intersection, and having circumferentially extending unidirectional structural fibers embedded in a gluing substance that is a different material from the polymeric material. 34. The bicycle rim of claim 33 wherein the gluing substance has an elongation at break coefficient higher than that of the polymeric material. 35. The bicycle rim of claim 33 wherein the gluing substance has an intralaminar shear strength higher than that of the polymeric material. 36. The bicycle rim of claim 31, wherein the first and third layers run parallel to define radially extending sidewalls having the wings. 37. A bicycle rim comprising: first, second, and third layers of composite material that define the rim's structure and a circumferentially extending enclosed space in the structure; the first and second layers have portions that are parallel with each other and portions that diverge from each other such that the diverging portions of the first and second layers form two boundaries of the circumferentially extending enclosed space; the third layer has portions that are parallel with the first and second layers respectively and a portion between those parallel portions that diverges from both the first and second layers and forms a third boundary of the circumferentially extending enclosed space, so that the circumferentially extending enclosed space is enclosed by the three boundaries; and a circumferentially extending reinforcement element of unidirectional structural fibers within the circumferentially extending enclosed space. 38. A bicycle rim made of composite material comprising structural fibers incorporated in a polymeric material, the rim comprising a plurality of walls; at least one intersection where at least one wall intersects at least one other wall; a gluing substance different from the polymeric material of the composite material; and at least one circumferential reinforcement element having circumferentially extending unidirectional structural fibers embedded in the gluing substance and extending at the at least one intersection of the walls of the rim. 39. A bicycle rim made of composite material comprising structural fibers incorporated in a polymeric material, the rim comprising a plurality of walls; at least one intersection where at least one wall intersects at least one other wall; a gluing substance different from the polymeric material of the composite material; and at least one circumferential reinforcement element having circumferentially extending unidirectional structural fibers incorporated in a polymeric material and embedded in the gluing substance and extending at the at least one intersection of the walls of the rim.