The Ultimate Guide to RC Shock Oil Charts: From Weight to cSt Conversion
When your RC car bounces uncontrollably over rough terrain or slides unpredictably through corners, your shock oil weight—or mismatch—is often the culprit. For professional RC enthusiasts and competitive racers, understanding shock oil viscosity isn’t just technical trivia; it’s the difference between podium finishes and perpetual frustration. The term “W” in oil weights stands for “Winter” in automotive contexts, but in RC applications, it simply denotes viscosity grade (e.g., 20W Oil, 30W). This viscosity directly governs how quickly your suspension reacts to impacts and transfers weight during acceleration or braking.
What Does the “W” Mean in RC Oil?
The “W” suffix in oils (like 30W oil or 40W oil) is a holdover from automotive engine oils, where it signaled winter viscosity ratings. In RC shock fluids, however, it has evolved to represent a standardized viscosity grade unrelated to temperature performance. Lower “W” numbers (e.g., 10W, 20W) indicate thinner oils that flow faster, ideal for smoother surfaces. Higher numbers (e.g., 60W oil, 70W oil) denote thicker oils for aggressive damping on rough tracks.
Unlike automotive oils, RC-specific oils avoid additives that could damage plastic components or seals. Brands like Yokomo and Red Line prioritize chemical stability to prevent corrosion of gears or shock internals—critical for longevity in high-stress RC systems.
How to Convert cSt to Oil Weight
RC oils use two measurement systems: kinematic viscosity (cSt) and empirical weight (W). While cSt (centistokes) quantifies flow resistance under gravity, “weight” is a simplified industry shorthand. No universal formula exists, but manufacturers publish approximate equivalencies:
Low viscosity: 150–350 cSt ≈ 10W–20W
Medium viscosity: 500–800 cSt ≈ 30W–40W
High viscosity: 1,000+ cSt ≈ 50W+
For example, Ultimate Racing’s Differential Oil 5000cSt behaves similarly to a 80W–90W gear oil, providing extreme film strength for high-load differentials. Always prioritize cSt values for precision tuning—weight classifications vary between brands.
RC Shock Oil Conversion Chart
Selecting the right shock oil weight depends on driving style, track surface, and vehicle weight. Use this reference chart to match cSt to common “W” ratings:
| Oil Weight (W) | cSt @ 104°F (40°C) | Track/Load Conditions | Vehicle Reaction |
|---|---|---|---|
| 10W | 80–110 | Indoor carpet, polished concrete | Lightning-fast steering response |
| 15W | 120–150 | High-grip asphalt, on-road | Reduced chassis roll in sweepers |
| 20W | 160–200 | Clay short course, moderate jumps | Controlled landing, minimal bounce |
| 25W | 210–250 | Hard-packed dirt, stadium trucks | Balanced bump absorption & corner stability |
| 30W | 260–320 | Blue-groove clay, 1/8 buggies | Progressive damping on acceleration squat |
| 35W | 330–400 | Loamy soil, trail trucks | Suppresses chassis pitch on whoops |
| 40W | 410–500 | Rocky terrain, crawlers | Prevents bottoming on ledges |
| 45W | 510–600 | Sandy desert, high-speed runs | Controls shock fade at 40+ mph |
| 50W | 610–750 | Muddy courses, monster trucks | Maintains damping in viscous conditions |
| 55W | 760–900 | BMX tracks, backflip-heavy rigs | Ultra-slow rebound for multi-rotational landings |
| 60W+ | 910–1,200 | 1/5 scale gas rigs | Handles 15+ lb vehicle loads |
RC Shock Oil Viscosity Conversion Guide
Note: Temperatures above 90°F (32°C) may require one step thicker oil.
Thicker oils (e.g., 60W–70W) slow suspension rebound, preventing “bounce” on jumps. Thinner oils (e.g., 20W–30W) allow faster weight transfer for responsive cornering.
RC Differential Oil Chart
Differential oil dictates power distribution between wheels. Thicker oils “lock” the diff, forcing both wheels to spin equally—ideal for high-traction launches. Thinner oils allow wheel-speed differentiation, aiding cornering:
| Vehicle Platform | Front Diff (cSt) | Rear Diff (cSt) | Center Diff (cSt) | Handling Profile | U.S. Track Reference |
|---|---|---|---|---|---|
| 1/10 Touring Car | 5,000 | 3,000 | N/A | Rotates mid-corner | ROAR asphalt nationals |
| 1/8 Nitro GT | 300,000 | 50,000 | N/A | Late-brake entry, stable exit | Vegas Speedway |
| 1/10 SCT 4WD | 100,000 | 30,000 | 50,000 | Square off berms | Dirt Nitro Challenge |
| 1/8 e-Buggy | 20,000 | 7,000 | 10,000 | Floats over rhythm sections | Glen Helen RC Park |
| 1/10 Drift Car | 200,000 | 500,000 | N/A | Sustained slides @ 45° angle | Super-G drift arena |
| 1/10 Rally | 50,000 | 10,000 | 30,000 | Loose gravel flickability | New England Forest Rally |
| 1/6 Scale Crawler | 500,000 | 1,000,000 | 300,000 | Creep torque, zero tire slip | King of the Hammers |
| 1/5 Baja 5B | 20,000 | 15,000 | 50,000 | Powerslides on dirt fire roads | Johnson Valley OHV |
Differential Oil Tuning Guide
For 1/8 GT models, veterans recommend 300,000cSt front/50,000cSt rear for late-braking setups. Reduce front viscosity to 50,000cSt if traction is minimal.
RC Shock Oil Chart by Terrain
| Terrain Type | Shock Oil (cSt) | Setup Notes | Suspension Geometry Tips |
|---|---|---|---|
| Indoor Carpet (RCP) | 100–150 | 30% softer springs than outdoor | Toe-in: +1° front, -0.5° rear |
| Blue-Groove Clay | 250–350 | 4mm preload, progressive pistons | Sway bars: 2.8mm front, 2.4mm rear |
| Hard-Pack Dirt Oval | 180–240 | High-roll center, 0° camber rear | Ride height: 22mm F / 24mm R |
| Loam MX Tracks | 400–500 | 50wt oil, digressive damping holes | Shock angle: 40° from vertical |
| Desert Sand Washes | 550–700 | Twin-tube shocks, external reservoirs | Limit rebound to 50% of total travel |
| Rock Crawling | 300–400 | Slow-rebound pistons, no sway bars | Articulation: 60°+ required |
| Mud Bogs | 800–1,000 | Wiper seals + boots, 2.0mm bleed hole | 30% stiffer springs than dry setup |
| Paved Oval (NASCAR) | 200–280 | Symmetric damping, 35% droop | Negative wedge: 2° right-side bias |
- Carpet tracks: Use 100cSt front / 130cSt rear to combat traction roll.
- Jump-heavy tracks: Add 100cSt to stock recommendations (e.g., 400cSt → 500cSt).
- Crawling: 350cSt oil + 90wt silicone grease in seals prevents stiction.
For digressive shock systems (common in performance RC models), thicker oils (50W+) enhance low-speed damping without harshness—similar to full-scale coilovers.
While charts provide starting points, advanced racers adjust oil weight based on:
- Temperature: Add 5W per 15°F drop below 50°F.
- Chassis weight: Heavy rigs need 10W–20W thicker oil.
- Driving style: Aggressive drivers prefer thicker oils to mask errors.
Red Line’s Heavy ShockProof® oil exemplifies niche formulations. Its 75W90-equivalent film strength (despite 250,000cSt viscosity) is favored for spool differentials in NHRA Top Fuel cars—and equally effective in RC drift cars.
The fluid inside your shocks and diffs is liquid engineering. Don’t just pour—tune with intent.
Maintenance Alert: Replace shock oil every 10 battery packs (electrics) or 2 gallons of fuel (nitro). Differential oils last 2× longer. Always use nitrile gloves – silicone oils degrade latex!