US Patent 7231867 Rotary damper

A rotary damper for damping oscillation of a motorcycle front tire includes a vane swingably mounted inside the rotary damper between left and right oil chambers, passages placing the oil chambers in fluid communication with one another, front chambers in communication with the passages to secure a pressure-receiving area adjacent the vane when the vane is at one of its extreme swing positions and begins swinging back towards the center of the damper, and grooves in fluid communication with the front chambers, wherein the grooves are formed shallower than the front chambers, and the passages are opened to the bottom of said grooves.