Wheel suspension system for bicycle

A wheel suspension system for a bicycle comprising:

• a pair of left and right sliding tubes secured to a steering bracket which is rotatably supported in a front portion of a body frame of the bicycle;
• a pair of left and right fork legs supporting a front wheel and slidably receiving a corresponding one of said sliding tubes;
• a pair of shock absorber assemblies respectively disposed between associated sliding tubes and said fork legs;
• each said shock absorber assembly including
• a piston body defining an upper chamber at a side of said sliding tube and a lower chamber at a side of said fork leg;
• a first valve disposed in a piston at a side of said upper chamber and normally biased for closing a compression stroke flow passage for fluid flow from said lower chamber to said upper chamber;
• a second valve disposed in said piston body at a side of said lower chamber and responsive to a fluid pressure difference between said upper and lower chambers during an extension stroke to open an extension flow passage for fluid flow from said upper chamber to said lower chamber;
• and
• a flow restrictive communication passage constantly establishing fluid communication between said upper and lower chambers in a limited fluid flow rate,
• wherein said second valve comprises a disc valve which comprises an inner annular portion, an outer annular portion and a connecting portion extending between said inner and outer annular portions, said inner annular portion being secured on said piston body, and said outer annular portion is located at a position closing said extension stroke flow passage, and
• wherein a spring seat is provided for a valve spring of said first valve, which spring seat is adjustable along an axial position for varying a spring force to be exerted on said first valve with an adjusting means externally inserted into said sliding tube in a rotatable fashion, said piston body being mounted on a lower end of the sliding tube, said sliding tube having an upper plug member provided on an upper end portion thereof and including an operation member rotatably supported on said plug member, and an adjusting pipe operably connecting said operable member to said adjusting means.