Exhaust system for saddle-ride type vehicle

A muffler 6 of a generally triangular shape in side view is provided and the interior thereof is partitioned into first to third expansion chambers 23-25. A manifold pipe 5 is connected to the second expansion chamber 24 as a middle chamber sideways from a lower portion of the same chamber and is accommodated therein so as to face upward. A catalyst is accommodated in the interior of the manifold pipe 5 and exhaust gas flowing out from an open end 5a of the manifold pipe is expanded into the second expansion chamber 24. A short-circuiting aperture 30 is formed in a second separator 22 and is opened and closed with an exhaust valve installed within the adjacent third expansion chamber 25. The exhaust valve is normally closed, and is urged in its closing direction by spring means. When the exhaust pressure becomes a predetermined magnitude, the exhaust valve opens automatically, allowing the exhaust gas to flow out into the third expansion chamber 25 through the short-circuiting aperture 30, thereby controlling the exhaust pressure.