The Yokomo RP-113375 RP Ultra Shock Oil #37.5 is a silicone-based shock oil supplied in a 40cc bottle and marked purple for quick identification. The RP Ultra line was revised to offer finer increments across common viscosities, helping drivers and tuners match damping feel more closely without changing other hardware.
As a shock fluid, its role is purely damping: it controls piston flow and rebound rates inside R/C shock bodies. Use it to refine compressive and rebound behaviour during suspension setup, especially when seeking small, repeatable changes between runs. The purple color code helps when you keep multiple viscosities on the bench.
Installation is straightforward for standard threaded shock bodies: drain the old oil, clean components, refill to the recommended level for your shock design, then compress the shock several times to purge trapped air and seat the piston. For consistent results, use the same filling method and check for foam or entrained air before final assembly.
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