GB2501894A - Bicycle fork with wide crown - Google Patents

Abstract

A bicycle wherein the front fork 20 comprises a substantialy horizontal member 21 extending across the top the fork, the ends 26 of the horizontal member being aligned to the middle of the knees of a rider 10 in a normal riding position, and a pair of fork members 23 extending downwards from either end of the horizontal member 21 and inclined towards one another, the fork members 23 to engage opposite ends of a front axle 16 of the cycle to the front wheel in position between the lower ends of the fork members 23.

Description

CYCLE

This invention relates to cycles and more particularly to the front forks of bicycles.

The legs of a cyclist, particularly a racing cyclist, are a source of significant drag.

According to the present invention cycle comprises a front pair of forks having a top portion thereof that would be substantially aligned mid-way across the leading knee of a rider in a normal riding position, and tapering downwards to the wheel mountings.

Preferably the front fork comprises a substantially horizontal memberjoining the forks, the ends of the horizontal member being aligned to the middle of the knees of a rider in a normal riding position, and a pair of inclined fork members extending downwards from either end of the horizontal member, each of the inclined fork members being inclined towards each other and engaging an end of the front axle of the cycle and holding the front wheel in position between the lower ends of the inclined fork members.

In these embodiments, for racing bicycles, the top portion of tile forks is around 1 7&nm wide, about 50% wider than the normal width of forks. The actual width can be tuned to individual riders if wished, but for general day to day use between 160 and 20Gmm is the optimum, with best performance at around 175mm.

There concern that for heavy use in a fork comprising a horizontal member, the join between the end of the horizontal member and the pair of inclined fork members may be a source of weakness. This may be overcome by placing bracing member in the angle between the horizontal member and the inclined forkmembers. Such a bracing member would increase the total air drag on a rider of the bicycle a little, negating some of the benefit of the invention. It has been found that if the brace is of an aerofoil section. with a wider rounded front and a rounded tapering rear, and is angled such that its front nose faces 1 0°from the horizontal, the additional drag caused by the bracing member is all but eliminated.

The horizontal member and the inclined fork members are preferably ovoid in section.

Preferably the inclined fork members are stepped inwards towards each other and the front wheel just above their lower ends. This arrangements ensures that the inclined fork member are further apart than normal forks for a greater part of their height, further modifying air flow around the legs of a rider.

It has been found that by adding a fairing to the rear of the horizontal member with its tail directed upwards slightly (say by 5°), brther drag reduction was achved.

Likewise rounding of the sharp corners between the horizontal member and the inclined fork members achieved some further reductions.

Further drag reductions can be achieved by applying an aerofoils section the lower part of the inclined fork members with the aerofoil tails directing airflow approximately 1 O°outboard.

The invention will now be more fully described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a conventional pair of forks used in racing bicycles; Figure 2 shows a head on view of a pair of forks according to a preferred embodiment mounted on a bicycle shows; Figures shows the forks of figure2 with a racing member: Figure 4 shows a modified pair of forks according to a preferred embodiment of this invention; Figure 5 is similar to figure 4, but without chamfering of the lower parts of the fork members of the fork, showing a fairing on the horizontal member.

In figure 1, a pair of conventional bicycle forks 1 comprises a crown which is attached to the headstock of a bicycle (not shown) and a pair of inclined fork members extending down from the crown. Attheir lower ends 4 slots are provided to receive the axle of the front wheel of a bicycle. It will be noted that in these conventional forks for a racing bicycle thofork members Sara inclined in such a way as to diverge from one another top to bottom.

In figure 2 a cyclist 10 is shown mounted in a bicycle 12, with the front fork 20, within which the front wheel 16 is mounted, attached to the front headstock 16 of the bicycle. The forks comprise a substantially horizontal member 21 with the crown 22 of the forks at is midpoint, the forks being connected to the headstock 14 at the crown 22. As can be seen from the figure, the length of horizontal member 21 is such its ends are roughly aligned with the leading knee 17 of the cyclist 10, in the rider's riding position. The horizontal member would be about 174mm long, in the range 160 to 200mm, for riders having a wider knees out riding position a longer horizontal member would be desirable; for riders with a knees in position a less long horizontal member may be preferred.

Extending downwards from each end of the horizontal member 21 are inclined fork members 23 forming the prongs of the fork. At their lower ends are slots 24 to receive the axle of wheel 16. Just above the slots, the inclined fork members 23 are stepped inwards at 25, thus ensuring the inclined fork members are in front of the rider's leading leg 18 for much of their height. The portion 28 of the inclined fork members 23 which would not normally be in front of the rider's leading leg can be chamfered as described in figure 4.

There was some concern that the joint 26 between the horizontal member 21 and inclined fork members 23 would be a source ot weakness. To overcome this, in one embodiment in tigure 3, a brace 30 is included. By providing the brace 30 with an rounded section 32 with a lading rounded nose 34 and extended round tail 36, such that the nose was pointing down 1 0°with respect to the tail, drag changes caused by the brace 30 were minimal (0.O5Newtons).

A further development of the invention is shown in tigure 4. Here the front fork again comprises a horizontal member 41 passing through the crown 42. Inclined fork members 43 extend down from the ends of the horizontal members 42. The lower portions of the inclined fork members are stepped 45, above the slots 44 to receive the front wheel axle. The joint 46 between the horizontal member and the inclined fork member is rounded for greater strength. The lower part 48 of the inclined fork members 43 are chamfered with an aerofoil section 47 whose tail directs air padding over portion 48 outwards by about 10 This chamfering, it has been found further reduces drag.

Figure 5 shows a par of forks similar to those in figure 4, but without the aerofoil section 47, otherwise all the components re identical to those of figure 4 with identical legends. However, in this case a failing 50 is attached to the horizontal member4l. The tairing is shaped in such a way as to direct air flowing over the horizontal member upwards towards the cyclist by about 5°.

It should be noted that in all the examples 2 to 5, the inclined fork members are inclined from top to bottom towards one another, in contrast to the existing racing fork design where the inclined fork members diverge from top to bottom.

The table below compares the drag reduction performance for various forks according to invention.

Example Description Total Drag (N) Reduction

Compared to Lower legs and Base Line (N) Forks 1 Base Line 13.82 - 2 Figure 2 -0.86 3 Figure 3 -0.81 4 Figure 4 (no -0.80 chamfer) FigureS -1.00 It can be seen that in the best example, the overall drag reduction on the forks and lower legs is over 7%.

It should be noted that although the horizontal members 21 and 41 have been described as one individual member, they can in practice be made up of a plurality of members aligned generally horizontally; for ease of manufacture it may comprise two portions joined together by the crown 22 or 42.

Claims (4)

1. CLAIMS1 -A cycle comprises a pair of front forks having a top portion thereof that is substantially aligned mid-way across the leading knee of a rider in a normal riding position, and tapering downwards to the wheel mountings.
2. 2. A cycle according to claim 1 wherein he front fork comprises a substantially horizontal member extending across the top the forks, the ends of the horizontal member being aligned to the middle of the knees of a rider in a normal riding position, and a pair of fork members extending downwards from either end of the horizontal member and inclined towards one another, the fork members to engage opposite ends of the front axle of the cycle to the front wheel in position between the lower ends of the fork members.
3. 3. A cycle according to claim 2 wherein the horizontal member is between 160mm and 200mm long.
4. 4. A cycle according to claim 3 wherein the horizontal member is about 175mm long.A cycle according to any one ot claims 2 to 4 including a bracing member in the angle between the horizontal member and the each fork member 6. A cycle according to claim S wherein the bracing member is shaped to direct air passing over it upwards about 10°from the horizontal.7. A cycle according any preceding claim in which the forks are stepped inwards toward the front wheel above the wheel mounting position in the forks.8-A cycle according to any preceding claim wherein the horizontal member and the forks members are ovoid in section.9. A cycle according to any one of claims 2 to 8 wherein the horizontal member has a fairing on its trailing edge said fairing having a tail directed upwards slightly by about °.1 O.A cycle according to any preceding claim in which the lower portions of the fcrk members have aerofoil tails directing airflow approximately 100 outboardfrom the cycle 11.A cycle substantially as hereinbetore described with reference to the accompanying drawings. -