The Yokomo RP-113250 RP Ultra Shock Oil #25 is a silicone-based damping fluid for RC shock absorbers, offered in a color-coded yellow bottle with a 40cc fill. The RP Ultra series has been refreshed to provide finer viscosity increments across core ranges, allowing more granular changes to compression and rebound behaviour without changing hardware.
In practice the oil influences damping speed and feel: higher viscosity increases damping resistance for slower compression and rebound, lower viscosity reduces resistance for quicker response. Using a mid-range grade such as #25 is a common step when balancing on-track stability versus responsiveness, and the color coding helps swap bottles quickly during setup sessions.
When evaluating shock oil for tuning, consider consistency between left and right units, air bleed and shaft movement to avoid trapped air affecting damping, and small incremental changes to isolate handling effects. The RP Ultra labeling and finer viscosity steps simplify this iterative approach for racers and hobbyists focused on suspension setup.
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