How to pick the right shock oil weight for your RC. Covers cSt vs WT, what number to start with for which vehicle, and how to step it up or down based on what the car's doing.
Viscosity is a fluid's resistance to flow. In a shock, it's the thing that decides how hard the piston is to push through the oil, which is what damping is. It controls compression, rebound, and how the suspension behaves overall.
Thicker oil = more damping resistance. Thinner oil = less. Get the number right and the suspension works with you; get it wrong and the shocks fight the chassis.
Two ways of measuring the same thing. cSt (centistokes) is the precise SI unit and what most modern brands use. WT (weight) is older RC hobby terminology that's still around. Different scales, same property — and conversions between them are approximate, so always go by cSt when you can.
Rough conversion (varies slightly between formulations):
| cSt (Rhodex) | WT (Common) | Damping |
|---|---|---|
| 50 cSt | ~5 WT | Ultra-light |
| 100 cSt | ~10 WT | Very light |
| 150 cSt | ~15 WT | Light |
| 200 cSt | ~20 WT | Light-medium |
| 250 cSt | ~25 WT | Light-medium |
| 300 cSt | ~30 WT | Medium-light |
| 350 cSt | ~35 WT | Medium |
| 400 cSt | ~40 WT | Medium |
| 450 cSt | ~45 WT | Medium-firm |
| 500 cSt | ~50 WT | Firm |
| 600 cSt | ~60 WT | Firm-heavy |
| 700 cSt | ~70 WT | Heavy |
| 800 cSt | ~80 WT | Very heavy |
| 1000 cSt | ~100 WT | Maximum |
Different brands publish different cSt-to-WT conversions. The closest approximation is cSt ÷ 10 ≈ WT, but exact figures vary. When changing brands, always reference the cSt number — it's the actual physical measurement, not the marketing number.
Three factors influence your shock oil viscosity choice:
Smaller RCs use lighter oils. Larger RCs use heavier oils. The principle: heavier vehicles need more damping force to control suspension movement.
Smoother surfaces need less damping (lighter oils). Rougher surfaces need more damping (heavier oils).
Aggressive drivers benefit from firmer oils for control. Smoother drivers can run lighter oils for compliance.
Most racers run different viscosities front and rear to tune chassis balance:
Standard tuning convention: rear is typically slightly heavier than front for most touring and off-road buggies, with adjustments based on chassis-specific behavior.
Some brands sell limited viscosities and suggest blending to hit weights in between. We don't.
Silicone oils don't blend linearly. Mixing 350 cSt with 450 cSt doesn't give you a clean 400 cSt — the actual result depends on temperature, base oil chemistry, and how long the mix settles. For a racer chasing setup repeatability, "approximately" is the wrong answer.
Rhodex covers 20 viscosities from 50 cSt to 1000 cSt, with 50 cSt steps through the working range. Every weight a racer needs, bottled to spec. Pick the number, fill the shock, run the same setup next race.
Shock oil heats up during a run. Generic oils suffer "viscosity fade" — they thin out as they warm, so the damping changes mid-race. The 400 cSt you started with might be behaving more like 350 cSt by the end of the heat.
Rhodex Silicone Performance Fluid is stabilised against this. The viscosity at room temperature is essentially the viscosity at race temperature, which is what makes setup notes actually useful between runs.
Tuning isn't about finding the one "right" oil. It's about systematic adjustment from a known starting point. The reliable approach: