Patent ID: 7759293

Claim:
A method for improving damping force and initial damping properties of a shock absorber and for enhancing ride comfort of a vehicle equipped with the shock absorber comprising a step of using a hydraulic oil composition for the shock absorber, wherein the hydraulic oil composition comprises a lubricating base oil, at least one viscosity index improver and at least one fluorine-modified silicone oil, wherein the at least one viscosity index improver is selected from the group consisting of an olefin (co)polymer-based viscosity index improver with a weight-average molecular weight of 250,000 to 350,000 and a polymethacrylate-based viscosity index improver with a weight-average molecular weight of 150,000 to 250,000, wherein the hydraulic oil composition has a kinematic viscosity at 40° C. of 8 to 15 mm 2 /s, and wherein the at least one fluorine-modified silicone oil is contained in the hydraulic oil composition in an amount of 1 to 100 ppm by mass based on a total mass of the hydraulic oil composition, has a kinematic viscosity at 25° C. of 50 to 2,000 mm 2 /s, and is represented by formula (1): wherein groups R are each independently a hydrocarbon group and all or part of the groups R are substituted with a fluoroalkyl group having 1 to 10 carbon atoms.