Abstract
A bicycle has a front fork, within which the front wheel is mounted, attached to the head tube. Extending downwardly from each end of a lateral member are downwardly projecting forks, each comprising a primary portion, the respective primary portions extending downwardly and substantially parallel to each other. The longitudinal axes of both the main portion and a rider's lower leg are aligned. By aligning the wakes created by the forks and the lower leg a reduction in overall system drag is provided. Additionally or alternatively, the rear wheel may be provided between downwardly projecting stays, each comprising a primary portion, the respective primary portions extending downwardly and substantially parallel to each other. By aligning the downwardly projecting stays with the lower leg beneficial drag reduction is achieved.
Claims
1. A bicycle comprising a pair of front forks, each fork extending downwardly and substantially parallel to each other from a crown, the forks widely spaced apart from each other and a wheel mounted therebetween, wherein the widely spaced forks are each aligned with an axis of the lower leg of a rider in a normal riding position.
2. A bicycle as claimed in claim 1 wherein the fork spacing is in the range 180-240 mm.
3. A bicycle as claimed in claim 1 wherein the fork spacing is in the range of Q-factor plus 40-90 mm.
4. A bicycle as claimed in claim 1 wherein an end of each fork distal from the crown comprises an axle receiving formation.
5. A bicycle as claimed in claim 4 wherein each fork comprises a primary portion extending from the crown, the primary portion comprising a single substantially linear member and a secondary portion connecting the primary portion to the axle receiving slot.
6. A bicycle as claimed in claim 5 wherein the secondary portion is inclined inwardly relative to the primary portion.
7. A bicycle as claimed in claim 1 wherein the crown comprises one or more lateral members.
8. A bicycle as claimed in claim 7 wherein the crown comprises one or more extension members projecting upwardly from said one or more lateral members.
9. A bicycle as claimed in claim 8 wherein the extension members are in a common alignment with the forks or at least the primary portion of each fork.
10. A bicycle as claimed in claim 8 wherein the extension members comprise a lateral section at their upward end or are connected to one or more lateral members or a handle bar at their upward end.
11. A bicycle as claimed in claim 1 wherein the crown is connected to a head tube.
12. A bicycle as claimed in claim 1 wherein the bicycle comprises a pair of seat stays, each seat stay extending downwardly and substantially parallel to each other from a crown, the seat stays widely spaced apart from each other and a wheel mounted therebetween wherein the widely spaced stays are each aligned with the axis of the lower leg of a rider in a normal riding position.
13. A bicycle as claimed in claim 12 wherein the stay spacing is in the range 170-240 mm.
14. A bicycle as claimed in claim 12 wherein the stay spacing is in the range of Q-factor plus 40-90 mm.
15. A bicycle as claimed in claim 12 wherein the end of each stay distal from the crown comprises an axle receiving formation.
16. A bicycle as claimed in claim 15 wherein each stay comprises a primary portion extending from the crown, the primary portion comprising a single substantially linear member and a secondary portion connecting the primary portion to the axle receiving slot.
17. A bicycle as claimed in claim 16 wherein the secondary portion is inclined inwardly relative to the primary portion.
18. A bicycle as claimed in claim 12 wherein the crown comprises one or more lateral members.
19. A bicycle as claimed in claim 18 wherein the crown comprises one or more extension members projecting upwardly from said one or more lateral members.
20. A bicycle as claimed in claim 19 wherein the extension members are in a common alignment with the forks or at least the primary portion of each stay.
21. A bicycle as claimed in claim 18 wherein the extension members comprise a lateral section at their upward end or are connected to one or more lateral members or a saddle at their upward end.
22. A bicycle as claimed in claim 12 wherein the bicycle is provided with a saddle comprising a seat surface and a seat post wherein the seat post comprises two widely spaced limbs.
23. A bicycle as claimed in claim 22 wherein the widely spaced limbs have at least a portion separated by substantially the full width of the saddle.
24. A bicycle as claimed in claim 22 wherein the widely spaced limbs are connected to the edges of the seat surface.
25. A bicycle comprising a pair of seat stays, each seat stay extending downwardly and substantially parallel to each other from a crown, the seat stays widely spaced apart from each other and a wheel mounted therebetween, wherein the widely spaced stays are each aligned with an axis of the lower leg of a rider in a normal riding position.
26. A saddle for a bicycle, the saddle comprising a seat surface and a seat post wherein the seat post comprises two widely spaced limbs wherein the widely spaced limbs are at least partially aligned with an axis of the upper leg of a rider in a seated riding position.
27. A method of fitting a bicycle for a rider, the method comprising the steps of measuring the lower leg separation of the rider in their normal riding position; and: providing a bicycle comprising a pair of front forks, each fork extending downwardly and substantially parallel to each other from a crown, the forks widely spaced apart from each other and a wheel mounted therebetween, wherein the fork separation of the bicycle is matched to the measured lower leg separation of the rider; and/or a providing a bicycle comprising a pair of seat stays, each seat stay extending downwardly and substantially parallel to each other from a crown, the seat stays widely spaced apart from each other and a wheel mounted therebetween, wherein where the seat stay separation is matched to the measured lower leg separation of the rider; and/or providing a bicycle with a saddle comprising a seat surface and a seat post wherein the seat post comprises two widely spaced limbs wherein where the limb separation of the seat post is matched to the measured hip separation of the rider.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:
[0060] FIG. 1 shows a head on view of a conventional pair of front forks of a racing bicycle;
[0061] FIG. 2 shows a head on view of a racing bicycle with a pair of front forks according to one prior art document;
[0062] FIG. 3 shows a head on view of a racing bicycle with a pair of front forks according to one embodiment of the present invention;
[0063] FIG. 4 is a schematic diagram illustrating the variation of the drag coefficient of a cylinder with respect to Reynolds number;
[0064] FIG. 5 is a schematic cross-sectional view illustrating different possible fork cross-sectional profiles;
[0065] FIG. 6a shows a head on view of a racing bicycle with a pair of front forks according to an alternative embodiment of the present invention;
[0066] FIG. 6b shows a head on view of a racing bicycle with a pair of front forks according to a further alternative embodiment of the present invention;
[0067] FIG. 7 shows a schematic rear view of a conventional pair of seat stays of a racing bicycle;
[0068] FIG. 8 shows a schematic rear view of a racing bicycle with a pair of seat stays according to one embodiment of the present invention;
[0069] FIG. 9a shows a schematic rear view of a racing bicycle with a pair of seat stays according to an alternative embodiment of the present invention;
[0070] FIG. 9b shows a schematic rear view of a racing bicycle with a pair of seat stays according to a further alternative embodiment of the present invention;
[0071] FIG. 9c shows a schematic rear view of a racing bicycle with a pair of seat stays according to a still further alternative embodiment of the present invention;
[0072] FIG. 10a shows an embodiment of a bicycle frame incorporating front forks and seat stays according to the present invention;
[0073] FIG. 10b shows a further embodiment of a bicycle frame incorporating front forks and seat stays according to the present invention;
[0074] FIG. 11a shows an embodiment of a saddle for a bicycle according to the present invention;
[0075] FIG. 11b shows an alternative embodiment of a saddle for a bicycle according to the present invention;
[0076] FIG. 11c shows a further alternative embodiment of a saddle for a bicycle according to the present invention;
[0077] FIG. 11d shows a saddle according to FIG. 11a fitted to a bicycle frame according to FIG. 10a or FIG. 10b; and
[0078] FIG. 12 is a schematic diagram illustrating the splitter plate effect exploited by a pair of widely spaced rear stays according to the present invention.
DETAILED DESCRIPTION
[0079] Turning now to FIG. 1, a pair of conventional bicycle forks 1 comprises a crown 2 which is attached to the headstock of a bicycle (not shown) and a pair of inclined forks 3 extending downwardly from the crown 2. At the lower end of forks 3 are provided axle receiving slots 4. This enables the axle and hence the front wheel (not shown) of the bicycle to be fitted between the forks 3. As can be seen clearly in FIG. 1, the conventional forks 3 diverge outwardly away from the crown 2. Additionally, such forks 3 are relatively closely spaced with respect to a wheel fitted therebetween.
[0080] Turning now to FIG. 2, a cyclist 10 is shown in a normal riding position on a bicycle 12 as disclosed in GB2501894. The bicycle 12 has a front fork 20, within which the front wheel 16 is mounted, attached to the head tube 14 of the bicycle 12. The crown comprises a substantially horizontal member 21 connected to the headstock 14 at the midpoint 22. The length of horizontal member 21 is such that its ends are roughly aligned with the leading knee 17 of the cyclist 10, when in the riding position. Extending downwardly from each end of the horizontal member 21 are inwardly inclined forks 23. At their lower ends of the forks are axle receiving formations 24, typically slots or holes. The forks 23 comprise a more inwardly inclined secondary portion 25 just above the formations 24.
[0081] The front fork 20 of the bicycle 12 of FIG. 2 does provide for a drag reduction compared with a racing bicycle using a conventional front fork 1. Nevertheless, the drag reduction can be improved further by use of a fork according to the present invention
[0082] Turning now to FIG. 3, a cyclist 30 is shown in a normal riding position on a bicycle 32 according to one embodiment of the present invention. The bicycle 32 has a front fork 40, within which the front wheel 36 is mounted, attached to the head tube 34. The crown comprises a lateral member 41. As shown in FIG. 3, the lateral member 41 is substantially horizontal. Nevertheless, the skilled man will appreciate that the lateral member 41 could deviate from the horizontal upwardly or downwardly. The lateral member 41 connected to the headstock 34 at the midpoint 42. The length of horizontal member 41 is such that its ends are roughly aligned with the leading knee 37 of the cyclist 30, when in the riding position. Extending downwardly from each end of the lateral member 41 are downwardly projecting forks 43. At the lower ends of the forks 43 are axle receiving formations 44, typically slots or holes, for receiving the axle 35 of wheel 36. As shown in FIG. 3, the forks 43 each comprise a primary portion 46, the respective primary portions extending downwardly and substantially parallel to each other and an inwardly inclined secondary portion 45 just above the formations 44. This facilitates fitting conventional bicycle wheels 36 into the front fork 40. Nevertheless, the skilled man will appreciate that the inwardly inclined secondary portions 45 can be omitted if a wheel 36 with a longer axle is fitted or if the axle receiving formations 44 are provided on cross-members projecting perpendicular to the forks 43.
[0083] As can be seen clearly in FIG. 3, the longitudinal axes 31 of both the main portion 46 and the rider's lower leg 38 are aligned. When travelling forward, the forks 43 thereby create a wake in front of the rider's lower leg 38. The lower leg 38 will itself create a further wake. Accordingly, by aligning the wakes created by the forks 43 and the lower leg 38 a reduction in overall system drag is provided. This occurs because the presence of the forks with this alignment lowers the effective wind speed experienced by the riders legs. More specifically and additionally, the turbulent wake created by forks 43 pushes the onset of the drag crises phenomenon on the riders feet and legs to lower speeds resulting in further drag reduction.
[0084] Where close alignment between the axes 31 of the forks 43 and legs 38 can be maintained, considerable reductions drag can be achieved. In particular, rider testing has measured typical drag reductions of 0.5% to 2% in racing conditions and of up to 2.5% or 3% over a conventional fork. Furthermore, once the fork separation is adequately fitted for a rider, these drag reductions may be reliably achieved in racing conditions, which is not guaranteed in the prior art. Additionally, theoretical analysis has indicated that drag reductions of up to 5% may be achieved with particular riders, when the forks 43 are combined with seat stays 63 as discussed below. In practice, best results have been observed for riders with relatively slim legs. Nevertheless, significant benefits may still be measured for riders with relatively thicker legs.
[0085] Turning to FIG. 4 this comprises an illustration of the drag coefficient C.sub.D of a cylinder (a simple approximation of the rider's lower leg) in relation to the Reynolds number Re of the airflow. In normal cycling conditions, the airflow around the leg will have a laminar boundary layer and the drag coefficient will be determined by this relatively ordered flow, as illustrated by Leg Re on FIG. 4. The turbulent wake created by the forks 43 pushes the onset of the drag crises (as illustrated by arrow T) where turbulent boundary layer flow reduces drag to lower speeds. Accordingly, whilst the wide spaced forks 43 may increase the coefficient of drag of the bicycle frame considered in isolation, the consequent reduction of the coefficient of drag of the rider's lower legs by pushing the flow around the legs into the drag crises zone reduces the overall coefficient of drag of the rider and bicycle combination.
[0086] In use, to maximise benefits, the separation of the forks 43 is customised for a particular rider. This optimises benefits for particular riders based on their physical size and/or riding position. Nevertheless, good results can be obtained for a wide range of riders with fork 43 separation in the region of say 180-240 mm.
[0087] The forks 43 can have any suitable cross-sectional profile. In FIG. 5, substantially (a) circular, (b) ovoid, (c) airfoil and truncated airfoil based cross-sectional fork profiles are illustrated, relative to airflow direction F. Whilst the profiles illustrated in FIG. 5 are substantially symmetrical with respect to the airflow direction F, the skilled man will appreciate that the invention equally applies to asymmetrical profiles. The skilled man will further appreciate that the sections illustrated in FIG. 5 may be differently orientated to the airflow direction F, if desired.
[0088] FIG. 5 further illustrates at (e), (f) and (g) that forks 43 can be formed from a pair of fork members 43a, b rather than a single fork member 43. The pair of fork members 43a, b can be spaced (e) parallel to (or close to parallel to) the airflow direction F as shown, (f) perpendicular (or close to perpendicular to) the airflow direction F, or (g) offset both parallel to and perpendicular to the airflow direction F.
[0089] FIG. 5 further illustrates at (h), (i) and (j) that forks 43 can be provided with a concave or scalloped trailing edge 43z. This form of trailing edge can provide an improved drag performance in a given cross-wind or yaw airflow. In particular, the scalloped trailing edge 43z delays separation of the airflow. Whilst at a small yaw this may have a relatively small effect, at larger yaw angles, it may delay stall, with a corresponding larger effect on overall drag.
[0090] Turning now to FIG. 6a, a cyclist 30 is shown in a normal riding position on a bicycle 32 according to an alternative embodiment of the present invention. This embodiment differs from the previous embodiment in that the crown comprises extension members 47 projecting upwardly from the lateral crown member 41.
[0091] The extension members 47 comprise a substantially upward projecting section 48 which maintains a substantially common alignment with the main portion 46 of the forks and hence a substantially common alignment with the rider's lower leg 38. Accordingly, the extension members provide further improved drag performance for the combination of the bicycle 32 and rider 30, even if the overall frame drag is increased by the extension members 47. As is shown in FIG. 6a, the extension members 47 have a horizontal or substantially horizontal section 49 at their upward end. This allows connection to the stem. This may be required to ensure conformance with certain bicycle racing regulations.
[0092] Turning now to FIG. 6b, a cyclist 30 is shown in a normal riding position on a bicycle 32 according to a further alternative embodiment of the present invention. This embodiment differs from the embodiment of FIG. 6a in that the upward projecting section 48 of each extension member 47 is terminated at the handle bar 39 rather than a horizontal section 49 of the extension member 50. This can maintain alignment between the extension member 47 and the lower leg 38 right up to the handle bar. This embodiment can therefore provide increased drag reduction benefits, in circumstances where such non-conventional bicycle frames are permitted.
[0093] In the embodiments of both FIGS. 6a and 6b, the forks 43 can have cross-sectional profiles of the type shown in FIG. 5.
[0094] Turning now to FIG. 7, a schematic view of a pair of conventional bicycle seat stays 50 is shown. The conventional stays 50 comprise a crown 52 which is attached to the seat tube 51 of a bicycle and a pair of inclined stays 53 extending downwardly and rearwardly from the crown 52. At the lower end of stays 53 are provided axle receiving formations 54, typically slots or holes. A saddle 59 is provided at the top of seat tube 51. This enables the axle 55 and hence the rear wheel 56 of the bicycle, including gear set 57, to be fitted between the stays 53. As can be seen clearly in FIG. 7, the conventional stays 53 diverge outwardly away from the crown 52. Additionally, such stays 53 are relatively closely spaced with respect to a wheel fitted therebetween.
[0095] Turning now to FIG. 8, a schematic view of a pair of bicycle seat stays 60 according to the present invention is shown. The stays 60 are adapted to mount rear bicycle wheel 56 therebetween by connections to axle 55.
[0096] The stays 60 comprise a crown formed from a lateral member 61. As shown in FIG. 8, the lateral member 61 is substantially horizontal. Nevertheless, the skilled man will appreciate that the lateral member 61 could deviate from the horizontal upwardly or downwardly. The lateral member 61 which is connected to the seat tube 51 at the midpoint 62. The length of the lateral member 61 is such its ends are roughly aligned with the axis 31 of the lower leg 38 of a rider 30, when in the riding position. For simplicity, in FIG. 8 only the axis 31 is illustrated rather than the rider 30.
[0097] Extending downwardly from each end of the lateral member 61 are downwardly projecting stays 63. At the lower ends of the stays 63 are axle receiving formations 64 for receiving the axle 55 of wheel 56. As shown in FIG. 8, the stays 63 each comprise a primary portion 66, the respective primary portions 66 extending downwardly and substantially parallel to each other and an inwardly inclined secondary portion 65 just above the formations 64. This facilitates fitting conventional bicycle wheels 56 into the stay 60. Nevertheless, the skilled man will appreciate that the inwardly inclined secondary portions 65 can be omitted if a wheel 66 with a longer axle 55 is fitted or if the axle receiving formations 64 are provided on cross-members projecting perpendicular to the stays 63.
[0098] The alignment between the legs 38 and the stays 60 provides beneficial drag reduction for the leg 38 and stay 60 when considered together. This is a result of the splitter plate effect and is illustrated with reference to FIG. 12. In FIG. 12a, a cross-sectional plan of the lower leg 38 (approximated as a cylinder) and vortices 81a, 81b generated by airflow in the direction F is shown. As is shown, vortices of same rotation sense 81a are alternately shed by the ‘leg’ 38 with vortices of the opposite rotation sense 81b. Typically, there is a spacing of approximately 5 leg diameters (D) between each vortex of the same sense, thus indicating a vortex shed wavelength of 2.5D, although the skilled man will be aware that this vortex shed wavelength may vary with speed as well as leg diameter. As is shown in FIG. 12b, the provision of a stay 60 aligned with leg 38 within the vortex shed wavelength suppresses vortex formation in the wake of the leg 38. This can result in a corresponding reduction in the drag experienced by the leg 38. The separation 82 of the stays from a typical, reference or average position of the leg 38 in the direction of motion, during the cycling action may also therefore be adjusted to match the vortex shed wavelength for as much of the pedal stroke as possible.
[0099] As in the front forks 40 discussed above, where close alignment between the axes 31 of the stays 63 and legs 38 can be maintained, considerable reductions in drag (of the order of, say, 1% to 1.5%) can be achieved.
[0100] Turning now to FIG. 9a, an alternative embodiment of the seat stays 60 is shown. This embodiment differs from the previous embodiment in that the crown comprises extension members 67 projecting upwardly from the lateral crown member 61. The extension members 47 maintain a substantially common alignment with the main portion 66 of the stays for much of their length. As such, they maintain a substantially common alignment with the rider's lower leg 38. Accordingly, the extension members 67 provide further improved drag performance for the combination of the bicycle 32 and rider 30, even if the overall frame drag is increased by the extension members 67. As is shown in FIG. 9a, the extension members 67 can be connected or integrated into saddle 70.
[0101] Turning now to FIG. 9b, a further alternative embodiment of the stays 60 is shown. This embodiment differs from the embodiment of FIG. 9a in that the lateral crown member 61 is omitted.
[0102] Turning now to FIG. 9c, a further alternative embodiment of the stays 60 is shown. This embodiment differs from the embodiment of FIG. 9a in that the seat tube 51 ends close to the point where it is connected to the lateral members 61. In this embodiment, the saddle 59 is thus supported only by the extension members 67 and not by a conventional seat post.
[0103] In the embodiments of FIGS. 8, 9a, 9b and 9c the stays 63 can have cross-sectional profiles of the type shown in FIG. 5. Furthermore, if desired, the stays may be formed from a pair of parallel stay members, similar to the forks of FIG. 5 (e)-(g). Additionally, in the embodiments of FIGS. 9a, 9b and 9c, the main portion 66 of stays 60 and/or the extension members 67 may optionally have telescopic sections. This can facilitate adjustment of the height of saddle 59.
[0104] Turning now to FIG. 10, two alternative frame designs 101, 102 according to the present invention are illustrated. Each frame 101, 102 comprises a top tube 110, a down tube 120, chain stays 130, a stem 140 and a seat tube 150, as is known in the art. Each of the frame members 110-150 may have a cross-sectional profile in accordance with those disclosed in FIG. 5.
[0105] As is shown in FIG. 10a, the frame 101 comprises a set of front forks 40 similar to the embodiment shown in FIG. 6a, but where the extension members 47 connect to the stem 140 rather than the head tube and a pair of seat stays 60 according to the embodiment of FIG. 8. The frame 101 is further provided with a set of handle bars 139 comprising a substantially horizontal section 137 and a drop section 138. The frame 101 thereby provides a set of forks 40 that connect to the stem 141 connected to the head tube 140.
[0106] Track testing of a frame of the type shown in FIG. 10a has identified a drag reduction of the order of 1.5-4%. The drag reduction achieved in practice is also dependent upon the speed and upon the rider, in particular the rider shape and/or rider position.
[0107] As is shown in FIG. 10b, the frame 102 comprises a pair of seat stays 60 according to the embodiment of FIG. 8. The frame 102 differs from frame 101 in that the front forks 40 are according to the embodiment of FIG. 6b. Additionally, the handle bars 131 have a different form comprising a substantially horizontal section 132, forward projecting end bars 133 and forward projecting arm bars 134. Turning now to FIG. 11a, a saddle 70 comprises a seat surface 71 adapted to support a rider and a seat post 72. In the saddle shown, the seat post 72 comprises a pair of widely spaced limbs 73 and a trunk 74. The limbs 73 extend between the trunk 74 and the edges of the seat surface 71. The wide spacing is facilitated by the connection of the limbs 73 to the edges of the seat surface 71 rather than to the underside of the seat surface as is conventional. Indeed, in some embodiments, this can facilitate the provision of a saddle where the seat surface 71 and seat post 72 are integrally formed. This can provide a weight saving.
[0108] The trunk 74 may comprise a single integral member or two closely aligned limbs, each aligned limb integral with a respective limb 73. The trunk 74 thereby facilitates the adjustable fitting of the saddle 70 to a seat tube 51, 150 of a bicycle as is common in the art.
[0109] The bifurcated limbs 73 and/or the stem 74 can have a cross-sectional profile of the type shown in FIG. 5.
[0110] Turning to FIG. 11b and FIG. 11c, alternative saddles 70b and 70c are shown. The alternative saddle 70b differs from saddle 70 only in that the limbs 73b are curved in a ‘U’ form rather a ‘V’ form shown in FIG. 11a. The alternative saddle 70c differs from saddle 70 in that the limbs 73c extend downwardly parallel to each other and are joined to the trunk 74 by a lateral member 75 at their lower ends. Whilst a substantially horizontal lateral member 75 is shown, the skilled man will appreciate that the lateral member 75 may be curved or angled upwardly or downwardly as required or as appropriate.
[0111] Turning now to FIG. 11d, the saddle 70 of FIG. 11a is fitted to the seat tube 150 of a bicycle frame 101 or 102. As can be seen from this figure, the bifurcated limb 73 allows the saddle post 72 to lie close to the axes of the respective upper legs 33 of the rider. In this manner, each bifurcated limb 73 lies within the wake of the upper leg 33 during forward motion. As a result, the drag on the combination of seated rider 30 and saddle 70 is reduced, even if the seat post 72 alone could be expected to have an increased drag compared to a conventional saddle with a singular seat post.
[0112] The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded by the appended claims.
