The Yokomo RP-113375 RP Ultra Shock Oil #37.5 comes as a silicone shock fluid in a 40cc bottle, colour-coded purple for fast identification. The RP Ultra range was refined to give finer viscosity increments so drivers and tuners can match damping feel more closely without altering other hardware.
Its function is pure damping control: it manages piston flow and rebound rates inside R/C shock bodies. Apply it when you want to refine compression and rebound behaviour during suspension setup, especially to achieve small, repeatable handling differences between runs. The purple coding helps when you store multiple weights side by side.
Refilling standard threaded shock bodies is simple: remove old oil, clean all components, top up to the specified level for your shock design, then compress several times to expel air and bed the piston. Maintain the same filling routine to minimise variance and check for trapped foam before reassembly.
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