Patent Description:
The rear wheel of motorcycles is usually supported by a rear fork, with which a shock absorber is associated. The rear fork has two arms, between which the rear driving wheel is arranged. The two arms are connected to a joining structure, which is in turn pivoted to the frame of the motorcycle.

Turbulences that negatively affect the aerodynamic efficiency of the motorcycle are generated in the rear area of the motorcycle, between the rear driving wheel and the frame, and the rear fork.

In "<NPL>" illustrates a motorcycle with an upside down airfoil close to the rear driving wheel, and discloses the features of the preamble of claim <NUM>.

It would thus be desirable to improve motorcycles, in particular racing motorcycles, reducing the negative aerodynamic phenomena that are generated between rear driving wheel, rear fork and frame.

To overcome or reduce the aforesaid problems of motorcycles of the current art, a motorcycle is provided comprising: a frame, an engine mounted on the frame; a front steered wheel; a rear driving wheel; a fairing at least partially surrounding the engine and the frame and having a lower wall extending under the engine from a front area of the motorcycle toward the rear driving wheel; and a rear fork hinged to the frame about an axis parallel to a rotation axis of the rear driving wheel. The rear fork comprises two arms for supporting the rear driving wheel, connected to each other by a joining structure having a rear surface facing the rear driving wheel. Advantageously, in a side view a first portion of the rear surface of the joining structure and a rear portion of the fairing, which extends from the lower wall toward the rear fork, together form a diffusion channel for an air flow between the rear fork and the rear driving wheel, generated by the forward movement of the motorcycle. The diffusion channel improves the conditions of motion of the air in the area of the rear driving wheel and of the rear fork.

In practical embodiments, a second portion of the rear surface of the joining structure is curved and substantially parallel to the profile of the rear driving wheel.

In at least one angular position of the rear fork, in a side view, i.e., in a section along a vertical median plane of the motorcycle, the rear portion of the fairing can be substantially tangent to the first portion of the rear surface of the joining structure.

In substance, the rear portion of the fairing and the rear surface of the joining structure can define, in the vertical median plane of the motorcycle, a guide profile for the air flow around the rear driving wheel.

Further advantageous features and embodiments of the motorcycle are defined in the appended claims, which form an integral part of the present description.

The invention will be better understood by following the description and the accompanying drawings, which illustrate a non-limiting example of embodiment of the invention. More in particular, in the drawing:.

In the context of the present description, unless otherwise specified, the terms above, below, top, bottom, right, left, upper, lower, front, rear, in front, behind, and analogous terms defining spatial positions of elements or components of the motorcycle or air flows around it, refer to a condition with the motorcycle in normal ride attitude. The term "vertical" indicates a direction parallel to the direction of the force of gravity and the term "horizontal" indicates a direction orthogonal to the vertical direction. In <FIG> the arrows L and R indicate the left and right direction and the arrows U and D indicate the vertical upward and downward direction.

In general terms, and as will be described in greater detail hereunder with reference to a non-limiting exemplary embodiment, a motorcycle comprising a fairing with a front portion facing a front steered wheel is provided. The front portion comprises: a front opening extending for an upper part of the vertical extension of the front portion of the fairing; and a covering for a lower part of the vertical extension of the front portion of the fairing. The covering comprises a front outer surface and a rear inner surface, and divides a descending air flow, generated by the forward movement of the motorcycle, into an outer partial flow that laps the front outer surface, and an inner partial flow that laps the rear inner surface. In embodiments described herein, the front outer surface and the rear inner surface together form an aerodynamic profile with a leading edge positioned along the perimeter edge of the front opening of the fairing.

With reference to the embodiment illustrated in the accompanying drawings, a motorcycle <NUM> comprises a frame <NUM>, to which a seat <NUM> and an engine <NUM> are fixed. Frontally, the motorcycle has a front steered wheel <NUM>, connected to a handlebar <NUM> and associated with a suspension, which - in the example illustrated - comprises a front fork <NUM>. The motorcycle <NUM> further comprises a rear driving wheel <NUM>, connected to the engine <NUM> via a transmission, for example a chain, not shown. The rear driving wheel <NUM> is supported by a rear fork <NUM> pivoted to the frame <NUM> about a hinge axis A (<FIG>), parallel to the rotation axis of the rear driving wheel <NUM>.

The engine <NUM> is cooled by means of a liquid coolant, for example water. The heat extracted from the engine <NUM> must be dissipated into the environment. In the illustrated embodiment, for this purpose at least one radiator <NUM>, typically mounted between the engine <NUM> and the front steered wheel <NUM>, is provided. In the illustrated embodiment, there are two radiators <NUM>, for example one radiator for cooling the water (or other fluid coolant) and one radiator for cooling the lubricating oil. In general terms, the motorcycle <NUM> can comprise a single radiator, for example for water coolant or for lubricating oil, or two radiators, one for water and one for oil, as in the schematic example represented here. In the context of the present description and of the appended claims, the term liquid coolant is also meant as lubricating oil.

Although the features of the fairing described here are particularly advantageous in motorcycles that have at least one radiator, preferably positioned with its main surface orthogonal to the direction of movement of the vehicle, some advantages can also be achieved in motorcycles with air cooling and/or with a different position of the radiator or radiators. The direction of movement is meant as the direction of movement with the steering of the motorcycle not turned, i.e. traveling in a straight line.

When at least one radiator <NUM> is provided, the heat is removed by an air flow, generated by the movement of the motorcycle, which encounters the radiator <NUM> and passes through it, lapping the ducts through which the liquid coolant (water, oil) passes. In the embodiment illustrated, there are two radiators <NUM>.

The frame <NUM> and the engine <NUM> are at least partially protected by a front fairing <NUM>, which comprises a front windshield <NUM> to protect the handlebar and the on-board instrumentation, as well as the driver, over the front steered wheel <NUM>.

The fairing <NUM> also has a left side portion 21A and a right side portion 21B at least partly flanking the engine <NUM> and structured to deflect the air beyond the driver G of the motorcycle <NUM>, when the motorcycle is in movement. Reference number <NUM> indicates a bottom or lower wall of the fairing <NUM>, facing the ground on which the motorcycle is supported and which joins the left side portion 21A and the right side portion 21B of the fairing. The bottom <NUM> extends under the radiator <NUM> and under the engine <NUM> of the motorcycle <NUM>, and from a front portion of the fairing <NUM> toward the rear driving wheel <NUM>.

The front portion of the fairing <NUM> extends from the windshield <NUM>, behind the front steered wheel <NUM> and to the bottom <NUM>, and between the left side portion 21A and the right side portion 21B of the fairing. The front portion has a front opening <NUM> surrounded by an edge <NUM>. The front opening <NUM> allows the entry of the air flow generated by the forward movement of the motorcycle inside of the fairing toward the engine <NUM>. If at least one radiator is present, the air flow strikes the radiator, which is typically positioned inside the fairing <NUM>, behind the front opening <NUM>, between the edge <NUM> of the front opening <NUM> and the engine <NUM>.

The front steered wheel <NUM> and the front fork <NUM> form an obstacle that obstructs the movement of the air flow toward the inside of the fairing <NUM> and in particular toward the radiator <NUM> or the radiators <NUM>, when present.

The front opening <NUM>, which allows the cooling air to enter the radiator <NUM>, does not involve the whole front portion of the fairing <NUM>, but extends from a point of maximum height, adjacent to the windshield <NUM>, toward the bottom of the fairing <NUM>, only for a portion of the extension in height of the front portion of the fairing, due to the presence of a front covering <NUM>, which extends from the bottom <NUM> of the fairing <NUM> toward the windshield <NUM>. If the motorcycle has at least one radiator <NUM> positioned behind the opening <NUM>, at least one portion of the front surface of said at least one radiator is partially covered by the front covering <NUM> formed by the fairing <NUM>. This covering <NUM> forms, in the lower area of the front portion of the fairing <NUM>, a pocket (<FIG>), which partly covers the front surface, i.e., the surface facing the direction of movement of the motorcycle <NUM>, of the radiator <NUM>, in the example illustrated of the lower radiator <NUM>, while the upper radiator <NUM> is completely free, i.e., its front surface is more or less completely visible through the front opening <NUM> observing in the direction opposite to the direction of forward movement of the motorcycle <NUM>. The edge <NUM> that surrounds the front opening <NUM> is therefore not completely external to the useful surface of the radiator, but has a lower portion that is located at a height substantially higher than the lowest point of the radiator <NUM>.

The portion of fairing <NUM> that forms the covering <NUM> of the radiator <NUM> defines an aerodynamic profile, in the present context again indicated with the reference number <NUM>, as visible in particular in <FIG>. More in particular, the covering <NUM> comprises a front outer surface 31a facing forward with respect to the direction of forward movement (arrow FF) of the motorcycle <NUM>. The covering <NUM> further comprises a rear inner surface 31b facing in the direction opposite the direction of forward movement of the motorcycle <NUM> and hence facing the radiator <NUM>. The front outer surface 31a and the rear inner surface 31b join to form a leading edge 31c (see in particular <FIG>), which forms part of the edge <NUM> that surrounds the front opening <NUM>.

With reference to <FIG>, reference number 25A indicates the highest point of the edge <NUM> that surrounds the front opening <NUM>. Therefore, 25A is the upper end of the front opening <NUM>. Normally, this point 25A is located on the vertical median plane of the motorcycle <NUM>. In <FIG>, the letter H indicates the distance of the upper end of the front opening <NUM> from the bottom <NUM> of the fairing <NUM>. The letter h indicates the distance between the upper end 25A of the front opening <NUM> and the leading edge 31c of the aerodynamic profile formed by the covering <NUM>. The distance h is preferably equal to or greater than <NUM>% of the distance H. Preferably, the distance h is equal to or less than <NUM>% of the distance H. For example, the distance h can be between <NUM>% and <NUM>%, preferably between <NUM>% and <NUM>% of the distance H, and more preferably between <NUM>% and <NUM>%, or between <NUM>% and <NUM>% of H.

The aerodynamic profile <NUM>, and more precisely its front outer surface 31a, is joined at the sides to the left side portion 21A and to the right side portion 21B (<FIG>) of the fairing <NUM> and is joined at the bottom to the lower wall or bottom <NUM> of the fairing <NUM>. Preferably, the front outer surface 31a is tangent to the side portions 21A, 21B and to the bottom <NUM>, and defines a joining curve without corners, for aerodynamic purposes.

The rear inner surface 31b is located at a certain distance from the front surface of the radiator <NUM>, so as to form a channel for the entry of an air flow in a direction approximately parallel to the front surface of the radiator <NUM>, between said radiator and the rear inner surface 31b of the covering <NUM>.

In a side view, the front outer surface 31b of the covering <NUM> can be mainly convex, but can have a portion close to the leading edge 31c, with a concave shape, as can be seen in the accompanying drawings. In practice, in some embodiments, in a sectional view of the fairing <NUM> according to a vertical median plane, the front outer surface 31a has, in sequence and starting from the leading edge 31c, a profile with a first concave portion and a second convex portion. The convex portion continues downward until it joins to a lower outer surface of the portion of lower fairing <NUM> that extends under the engine of the motorcycle.

However, the front outer surface 31a is mainly (or completely) convex, i.e., it has a convexity facing forward, while the rear inner surface 31b is mainly (or completely) concave, i.e., has a concavity facing backward. In substance, the intersection between the vertical median plane of the motorcycle <NUM> and the portion of fairing that forms the covering <NUM> defines two curves, one mainly convex facing forward and the other mainly concave, facing backward.

The two surfaces 31a and 31b can be formed by two separate metal sheets, joined to each other along the leading edge 31c.

In advantageous embodiments, in a side view the part of front outer surface 31a of the covering <NUM> that defines the convex portion projects forward forming an ogival-shaped or bulb-shaped portion of the fairing <NUM>, which reduces the aerodynamic drag coefficient of the motorcycle.

The front outer surface 31a joins to the lower outer surface of the bottom <NUM> of the fairing defining an acceleration profile of the air flow that laps the front outer surface 31a and the lower outer surface of the fairing <NUM>, so as to generate a reduction in the air pressure, which increases the ground adhesion of the motorcycle during travel. In <FIG> this adhesion force is indicated with F1.

In advantageous embodiments, the rear inner surface 31b of the aerodynamic profile formed by the covering <NUM> extends from the leading edge 31c downward and slopes backward, toward the radiator <NUM>. In other words, in a side view the profile defined by the rear inner surface 31b along the median plane of the motorcycle <NUM> has a distance from the radiator that decreases moving from the leading edge 31c toward the lower part of the covering <NUM>, i.e., toward the bottom <NUM> of the fairing <NUM>, extending under the engine <NUM>. When the motorcycle <NUM> moves forward, the air flow entering the volume inside the fairing behind the surface 31b decelerates along said surface 31b, with consequent increase in pressure, which contributes to the adhesion force F1.

The function of the covering <NUM> described above is illustrated in particular in <FIG>. During the forward movement of the motorcycle <NUM>, an air flow F is generated between the front steered wheel <NUM> and the upper front part of the fairing <NUM>, which can flow both over and under a front mudguard <NUM> and which has a component directed downward. The upper part of the fluid stream forming the air flow F directly impacts the radiator <NUM>, with a high velocity component orthogonal to the front surface of the radiator <NUM>, so as to pass through the radiator <NUM>. The lower portion of the fluid stream forming the air flow F has a high vertical velocity component, directed downward. The portion of flow directed downward encounters the leading edge 31c and is divided into a front partial flow FA and into a rear partial flow FB.

In a side view, the front partial flow FA laps the front outer surface 31a of the covering <NUM> and is diverted (arrow FC, <FIG>) between the bottom <NUM> of the fairing <NUM> and the ground, generating a force directed downward as a result of the acceleration along the front outer surface 31a and the ogival portion defined thereby.

The rear partial flow FB laps the rear inner surface 31b of the covering <NUM> and penetrates the channel defined between the rear inner surface 31b and the front surface of the radiator <NUM>, lapping the front surface of the radiator <NUM> as a result of the component of velocity directed downward of the flow FB. The rear partial flow FB is decelerated with consequent increase in pressure and flows gradually through the radiator <NUM>.

The aerodynamic shaped profile of the front outer surface 31a and of the rear inner surface 31b limits the risk of separation of the fluid stream along the surfaces and thus improves the fluid-dynamic behavior.

The deceleration of the partial flow FB in the flow pocket or channel formed between the front surface of the radiator <NUM> and the rear inner surface 31b of the covering <NUM> pushes the air through the radiator <NUM>. The partial flow FB thus contributes efficiently to the removal of heat from the radiator <NUM>.

In this way, the air flow F generated between the front steered wheel <NUM> and the upper part of the fairing <NUM> is utilized optimally, to cool the fluid coolant of the engine <NUM>. Moreover, the covering <NUM> protects the inside of the fairing <NUM> from the entry of detritus and sharp objects, such as stones, which could damage mechanical members, such as the radiator. The inflow of hot air, pumped from the ground by the front steered wheel <NUM> in the event of very high environmental temperatures, is also reduced, with consequent improvement of the cooling conditions of the engine <NUM>.

In the embodiment illustrated in the accompanying drawings, and in particular in <FIG>, <FIG>, <FIG> and <FIG>, the rear fork <NUM> comprises two support arms <NUM> of the rear driving wheel <NUM>. The two arms <NUM> are connected to each other by a joining structure <NUM> which forms a block also defining the hinge connecting the rear fork <NUM> to the frame of the motorcycle.

The joining structure <NUM> comprises a rear surface <NUM> facing the rear driving wheel <NUM>. As can be seen in particular in <FIG> and <FIG>, in a side view, or more precisely in a sectional view along a vertical median plane of the motorcycle <NUM>, the rear surface <NUM> has a lower portion that is joined to a rear portion <NUM> of the fairing <NUM>. The rear portion <NUM> of the fairing extends from the bottom <NUM> of the fairing <NUM> upward and faces the ground and the rear driving wheel <NUM>.

In practical embodiments, the rear surface <NUM> can have, in aside view, or more precisely in a sectional view along a vertical median plane of the motorcycle <NUM>, a portion approximately parallel to the perimeter surface of the rear driving wheel <NUM>. In some embodiments, the profile of the rear surface <NUM> along a vertical median plane of the motorcycle, as shown in <FIG>, can be such as to define, together with the profile of the rear driving wheel <NUM>, a channel converging slightly in the direction of the air flow that is generated between the rear driving wheel <NUM> and the rear surface <NUM>.

In practical embodiments, in a vertical median plane of the motorcycle <NUM> the rear surface <NUM> of the joining structure <NUM> defines a profile or curve (shown in <FIG> and <FIG>), which is substantially tangent to the rear portion <NUM> of the fairing <NUM>, so as to form, together with the perimeter surface of the rear driving wheel <NUM>, an air diffusion channel.

In practice, on the vertical median plane of the motorcycle <NUM> the rear portion <NUM> of the fairing <NUM> and the rear surface <NUM> of the joining structure <NUM> form a curve whose first derivative is continuous in the area of transition from the rear surface <NUM> and the rear portion <NUM>.

In this way, the rear portion <NUM> of the fairing <NUM> and the rear surface <NUM> of the joining structure <NUM> define a guide profile of the air flow around the rear driving wheel <NUM>.

In some embodiments, the joining structure <NUM> and the rear portion <NUM> of the fairing <NUM> can be configured so as to maintain a continuity of the surface defining the diffusion channel of the air flow around the rear driving wheel <NUM> regardless of the pivoting movement of the rear fork <NUM> around the axis A, for example as a result of the load represented by the driver G, or as a result of movements caused by roughness of the ground and/or by dynamic effects. For example, for this purpose the two mutually tangent surfaces of the rear portion <NUM> of the fairing <NUM> and of the joining structure <NUM> can have areas slidably coupled to each other.

In the illustrated embodiment, the rear portion <NUM> of the fairing <NUM> has an upper end edge <NUM> (<FIG>) facing the fork <NUM>, which is spaced from said fork. Moreover, the upper end edge <NUM> is provided with a notch <NUM> facing the rear fork <NUM>. A deflector <NUM>, of a shape complementary to the notch <NUM>, is integral with the rear fork <NUM>. In an angular position of the rear fork <NUM> the deflector <NUM> is approximately flush with the inside of the notch <NUM> to form a substantially continuous surface. When the rear fork <NUM> rotates upward around the axis A with respect to the aforesaid position, the deflector <NUM> moves away from the rear portion <NUM> of the fairing <NUM> causing a gap <NUM> to open in the rear portion <NUM> of the fairing, in front of which gap the deflector <NUM> is positioned. This forms a guide profile for the air flow exiting from the inside of the fairing <NUM> through the gap defined by the notch <NUM>, forcing this flow through the channel defined between the perimeter surface of the rear driving wheel <NUM> and the rear surface <NUM> of the joining structure <NUM>.

In this way a guide for the air flow is obtained around the rear portion of the fairing <NUM> and between the rear surface <NUM> of the joining structure <NUM> of the fork <NUM> and the rear driving wheel <NUM>, improving the flow conditions, reducing phenomena of vorticity that cause an increase in the rolling resistance of the motorcycle and also optimizing cooling conditions of the rear driving wheel <NUM> as a result of the air flow guided in the flow channel.

Acceleration of the air flow around the rear portion <NUM> of the fairing <NUM> toward the rear surface <NUM> of the joining structure <NUM> also causes an aerodynamic effect with a force directed downward, which increases the ground adhesion of the motorcycle <NUM> (arrow F2 in <FIG>).

This adhesion can be further increased using an upside down airfoil <NUM> integral with the rear fork <NUM> and positioned under the plane on which the rotation axis of the rear driving wheel <NUM> and the hinge axis A of the rear fork <NUM> lie. The airfoil <NUM> is upside down, in the sense that the high pressure surface, along which the air flow decelerates, is facing upward and the low pressure surface, along which the air flow accelerates, is facing downward. The leading edge of the airfoil <NUM> is facing forward and the trailing edge is facing toward the rear driving wheel <NUM> and is located in front of the rear driving wheel <NUM> with respect to the direction of forward movement (arrow FF) of the motorcycle <NUM>.

In particularly advantageous embodiments, a rear mudguard <NUM> with a rear surface <NUM> facing the rear driving wheel <NUM> can be fixed to the rear fork <NUM>. In a side view, and in particular in a sectional view along a vertical median plane of the motorcycle <NUM>, the rear surface <NUM> of the rear mudguard <NUM> can be substantially tangent to the rear surface <NUM> of the joining structure <NUM>, as can be seen in particular in <FIG>. In substance, the rear surface <NUM> of the rear mudguard <NUM> intersects the vertical median plane of the motorcycle <NUM> along a profile that forms the extension of the profile defined by the intersection of the rear surface <NUM> and of the rear portion <NUM> of the fairing <NUM> with the vertical median plane.

This defines a flow channel extending around the rear driving wheel <NUM> for a portion of the extension of this later that can reach as far as the upper area of the rear driving wheel <NUM>, under the seat of the motorcycle <NUM> along which the air flow FE is guided. This flow channel provides an efficient guide for the air flow FE generated by the forward movement of the motorcycle <NUM>, a reduction in aerodynamic drag and an effective cooling on the rear tire.

<FIG> shows a view similar to the view of <FIG>, of an improved embodiment. In particular, this embodiment provides solutions aimed at optimizing the effect of the flow generated by the structure of the rear fork <NUM>, and in particular of its rear surface <NUM>, in combination with the rear portion <NUM> of the fairing <NUM>.

As can be seen in <FIG>, a shield <NUM>, which extends around the perimeter surface of the tire of the rear driving wheel <NUM>, is arranged between the two arms <NUM> of the fork <NUM>. As can be understood by looking at <FIG>, the shield <NUM> can be in the form of a wall with a three-dimensional curvature, substantially corresponding to the curvature of the tire of the rear driving wheel <NUM>, positioned at a certain distance from the tread of said tire. In practice, the surface of the shield <NUM> facing the rear driving wheel <NUM> can form an envelope of the rear driving wheel <NUM>, at a preferably constant distance therefrom.

The shield <NUM> has an upper portion 100a and a lower portion 100b. In the illustrated embodiment, the portion 100a has an angular extension equal to an angle α and the portion 100b has an angular extension equal to an angle β. In some embodiments, the angular extension of the two portions 100a, 100b, and hence the total angular extension of the shield <NUM>, can be fixed. A set of shields with different angular extensions can be provided to adapt the motorcycle <NUM> to different riding conditions, for the purposes clarified below. In other embodiments, the two portions 100a, 100b can be movable one with respect to the other, so as to overlap to a larger or smaller extent and consequently vary the total angular extension thereof. This variation can be controlled manually, for example by making the two portions 100a and 100b in two parts fixable one with respect to the other in variable angular positions. In other, more sophisticated, embodiments, the angular extension of the shield <NUM> can be modified with a servo-assisted system, optionally by means of a control accessible to the driver G during riding. For this purpose, an electric, pneumatic or hydraulic actuator can be provided. It would also be possible to control lengthening and shortening of the shield <NUM> by means of a mechanical control with an operating member positioned on the handlebar or otherwise accessible to the driver during riding.

The function of the shield <NUM> is to shield the tire of the rear driving wheel 13to a greater or lesser extent, as a function of its angular extension (α+β). In this way, by shielding the tire of the rear driving wheel <NUM> to a greater or lesser extent, the temperature of the tire can be adjusted, i.e., a greater or lesser cooling effect of the tire can be imparted as a result of the air flow conveyed in the channel formed by the rear portion <NUM> of the fairing <NUM> and by the rear surface <NUM> of the rear fork <NUM>.

The angular extension (α+β) of the shield <NUM> can be modified (manually or in a servo-assisted manner) as a function of the riding conditions, of the type of tire mounted, of the ambient temperature, of the type of road surface, etc. It would also be possible, in the case of servo-assisted operation, to automate the control of the angular extension of the shield <NUM> based on a temperature signal generated by a temperature sensor that detects the surface temperature of the rear tire.

Claim 1:
A motorcycle (<NUM>) comprising:
a frame (<NUM>);
an engine (<NUM>) mounted on the frame (<NUM>);
a front steered wheel (<NUM>);
a rear driving wheel (<NUM>);
a fairing (<NUM>) at least partially surrounding the engine (<NUM>) and the frame (<NUM>) and having a bottom (<NUM>) extending under the engine (<NUM>) from a front area of the motorcycle (<NUM>) toward the rear driving wheel (<NUM>); and
a rear fork (<NUM>) hinged to the frame (<NUM>) about an axis (A) parallel to a rotation axis of the rear driving wheel (<NUM>) and comprising two arms (<NUM>) for supporting the rear driving wheel (<NUM>), connected to each other by a joining structure (<NUM>) having a rear surface (<NUM>) facing the rear driving wheel (<NUM>);
characterized in that a first portion of the rear surface (<NUM>) of the joining structure (<NUM>) and a rear portion (<NUM>) of the fairing (<NUM>), which extends from the bottom (<NUM>) toward the rear fork (<NUM>), together form a diffusion channel for an air flow between the rear fork (<NUM>) and the rear driving wheel (<NUM>), generated by the forward movement of the motorcycle (<NUM>).