Everything you need to know about selecting the right shock oil viscosity for your RC. From cSt-vs-WT conversion to track-specific tuning recommendations.
Viscosity is the measurement of a fluid's resistance to flow. In RC shock oils, it's the single most important property — it determines how much your shock pistons resist movement, which controls compression damping, rebound damping, and overall suspension behavior.
Higher viscosity = thicker oil = more damping resistance. Lower viscosity = thinner oil = less damping resistance. Get this right, and your suspension works with you. Get it wrong, and your shocks fight your inputs.
Shock oils are measured two ways: cSt (centistokes) and WT (weight). Most professional manufacturers use cSt because it's a precise SI unit. WT is older terminology that's still common in the RC hobby. Both measure the same thing — viscosity — but they're not the same scale.
Approximate conversion (varies slightly by formula):
| 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.
Need a viscosity between two standard offerings? Mix them. Rhodex Silicone Performance Fluid is fully blendable. Equal parts of two viscosities give you approximately the average.
Note: This is approximate. Blending behavior is non-linear at the extremes (very high vs very low viscosities). For racing precision, use the closest standard viscosity rather than custom blends.
Shock oil heats up during racing. Generic shock oils suffer "viscosity fade" — they thin out as they heat, changing your damping mid-race. By the end of the run, your 400 cSt might be behaving like 350 cSt.
Rhodex Silicone Performance Fluid is heat-stable. The viscosity at room temperature is essentially the viscosity at race temperature. That consistency is why professional teams trust silicone-based shock oils, and why Rhodex specifically engineers for this property.
Setting up your shocks isn't about finding "the right" oil — it's about systematic adjustment. Here's the professional approach: