A straddled vehicle includes a duct part formed integrally with a lower case of an air cleaner and extending forward from the lower case in a vehicle front-rear direction, and a side cover including a duct formation portion placed outward of the duct part in a vehicle width direction. At least a portion of the side cover is assembled onto the duct part. A duct is defined by the duct part and the duct formation portion of the side cover.

A straddled vehicle includes a duct part formed integrally with a lower case of an air cleaner and extending forward from the lower case in a vehicle front-rear direction, and a side cover including a duct formation portion placed outward of the duct part in a vehicle width direction. At least a portion of the side cover is assembled onto the duct part. A duct is defined by the duct part and the duct formation portion of the side cover.

A volumetric expander for increasing the air intake between a throttle body and an intake manifold includes a throttle body neck, a manifold adapter, and a throttle body adapter. The manifold adapter and the throttle body adapter are positioned opposite each other along a intake tube of the throttle body neck, wherein a first air channel traversing along the intake tube is aligned with a first intake opening of both the manifold adapter and the throttle body adapter. Additionally, a second air channel is aligned with a second intake opening of both the manifold adapter and the throttle body adapter. A manifold gasket is positioned into the manifold adapter and creates an air tight seal between the manifold adapter and the intake manifold, while a throttle body gasket is positioned into the throttle body adapter and creates an air tight seal between the throttle body adapter and the throttle body.

An air intake duct of a motorcycle extends rearwardly from a front portion of a motorcycle body so as to pass laterally of the left side of a motorcycle frame structure, and incoming wind is supplied as an intake air through the air intake duct to a combustion engine. The air intake duct is divided in a widthwise direction of the motorcycle. An upper dividing face of the air intake duct is disposed inward of an intermediate position, in a motorcycle widthwise direction, of the air intake duct.

A combustion engine of a motorcycle has an engine rotary shaft extending in a vehicle widthwise direction. Incoming wind taken in from a front of a steering handle that is positioned in front of the combustion engine, is introduced through an air intake duct to the combustion engine. The air intake duct extends from the front of the steering handle to a rearward of a cylinder block so as to pass above a radiator and pass laterally of one side of the cylinder block.

An air intake duct, of a saddle-riding type vehicle, in which a flow velocity of an intake air is less likely to be reduced to enable prevention of reduction of an efficiency of a supercharger, is provided. The air intake duct of a motorcycle serves to supply incoming wind as the intake air to the supercharger for a combustion engine. The air intake duct has a passage area that is gradually reduced from an air intake port at a front portion toward a downstream portion connected to the supercharger at a rear portion.

An air intake duct of a motorcycle forms an air intake passage for supplying an intake air to a supercharger. The air intake duct forms a curve portion and is connected to the supercharger. The air intake passage has a transverse cross-section which is shaped such that a dimension in an orthogonal direction that is orthogonal to a radial direction of the curve portion is gradually reduced from the center of the curve portion toward an outer side, in the radial direction, of the curve portion.

Output performance of the engine may be maximized by a configuration in which air is supplied so as to maximize volumetric efficiency of the respective cylinders in a multi-cylinder engine including a plurality of cylinders.