After years of watching racers scratch their heads at the shock oil shelf, we reckon it's time someone explained this properly. The difference between 300cst and 500cst silicone oil might seem like numbers on a bottle, but get it wrong and your RC car will handle like a shopping trolley with a wonky wheel. Trust us, we've seen enough botched setups to know.

Here's the thing - silicone oil is the unsung hero of RC performance. It's in your shocks, your differentials, and if you're running nitro, it's probably saved your air filter more times than you realise. Yet most hobbyists treat oil choice like a guess rather than the calculated decision it should be. We've watched plenty of racers throw money at new motors and tyres when a simple oil change would've transformed their lap times.

The Australian climate throws unique challenges at our RC gear too. That 10,000cst diff oil that works perfectly on a mild Melbourne morning? It'll turn to treacle when the temperature hits 38 degrees in the arvo. Meanwhile, your mate running the same setup in Tassie wonders why his diffs feel loose. Understanding how silicone oil behaves isn't just technical knowledge - it's essential for consistent performance across our varied conditions.

So whether you're setting up a race buggy for your local track, tuning a crawler for the rocks, or just trying to stop your drift car from bouncing like a kangaroo, understanding silicone oil weights will genuinely change how your vehicles perform.

Understanding Silicone Oil Weights and What CST Actually Means

Right, let's cut through the confusion. CST stands for centistokes, which measures kinematic viscosity - basically how thick the oil is and how it flows. Think of it like this: water is about 1cst, honey is around 10,000cst, and that ancient bottle of diff oil in your toolbox that's gone weird is probably approaching peanut butter territory. The numbers on our shock oil bottles typically range from 100cst (super thin) to 1,000cst (pretty thick), while diff oils can go from 1,000cst right up to 1,000,000cst for locked diffs.

But here's what nobody tells you at first - these numbers aren't just arbitrary. Each weight creates specific damping characteristics that fundamentally change how your RC vehicle transfers weight, absorbs bumps, and puts power down. Run too light in your shocks and you'll bottom out on every jump. Too heavy and your suspension won't react fast enough for those washboard sections at the track. We've seen racers literally transform their lap times just by stepping up or down one oil weight.

The confusion often starts because manufacturers use different numbering systems. Some brands label by CST, others use weight numbers like 30wt or 40wt, and then Traxxas comes along with their own numbering that doesn't match anyone else's. Generally speaking, a 30wt oil is around 350cst, 40wt is about 500cst, but always check the actual CST rating if you're switching brands. We keep a conversion chart at the counter because honestly, even we get confused sometimes.

What really matters is understanding the relationship between weight and performance. Lighter oils (lower CST) give faster response but less damping - perfect for smooth tracks or when you need quick suspension movement. Heavier oils (higher CST) provide more damping and slower movement - ideal for rough surfaces or controlling chassis roll. Once you grasp this concept, tuning becomes logical rather than guesswork.

Shock Oil Selection That Actually Makes Sense

Your shocks are basically hydraulic dampers, and the oil weight determines how quickly they compress and extend. Get this right and your buggy floats over rough sections like magic. Get it wrong and you'll be picking up parts after every session. We start most people on 400-500cst (or 35-40wt) because it's a safe middle ground that works for general bashing, but honestly, that's like saying everyone should wear size 10 shoes.

Track surface dictates everything. On our local carpet track, racers run 250-300cst because the surface is predictable and they need quick suspension response. Head out to the dirt track on Sunday though, and those same drivers are running 500-600cst to handle the ruts and jumps. The looser and rougher the surface, the heavier you generally want to go. But - and this is important - driver preference plays a huge role. Some blokes love a firm setup, others want it soft as. There's no universal "correct" weight.

Front versus rear weight selection is where things get proper interesting. Running heavier oil up front (like 500cst front, 400cst rear) gives more steering and prevents nose-diving under brakes. Flip it around with lighter front oil, and you'll get more aggressive turn-in but might experience understeer on power. Most touring car racers run slightly heavier in the rear for stability, while buggy racers often go heavier up front for landing jumps.

Here's a trick we've learned over the years: if you're constantly bottoming out but don't want to lose small bump compliance, try going up just 50-100cst rather than making huge jumps. Small changes in shock oil make surprisingly big differences. We've watched racers chase setup problems with spring changes when a simple oil weight adjustment would've sorted it in minutes. Also, remember that shock oil breaks down over time - that 500cst oil might be performing like 400cst after a season of hard running.

Differential Oil and Why Weight Matters More Than You Think

Differential oil is where the real tuning magic happens, yet it's probably the most overlooked fluid in RC. Your diff oil weight literally controls how power transfers between wheels - run it too light and you'll get inside wheel spin in corners, too heavy and you might as well have a locked diff. The range here is mental too, from 1,000cst for maximum diff action all the way up to 1,000,000cst which essentially locks it solid. Most bashers never touch their diff oil and wonder why their Traxxas Slash won't hook up properly.

Centre diffs (on vehicles that have them) are particularly sensitive to oil weight. This controls front-to-rear power distribution and massively affects handling balance. Running thicker oil (30,000-50,000cst) sends more power to the rear for better straight-line stability and corner exit. Thinner oil (5,000-10,000cst) allows more diff action, helping rotation but potentially causing instability. We've seen racers drop seconds off lap times just by nailing their centre diff oil.

Front and rear diff tuning is equally critical but often misunderstood. In on-road cars, a common setup runs 3,000-5,000cst front and 1,000-3,000cst rear - this gives good turn-in while maintaining rear traction. For off-road, you might flip that completely, running lighter up front to reduce understeer in loose conditions. The key is understanding that thicker oil makes that diff act more like a locked unit, transferring more torque but reducing differential action.

Temperature absolutely hammers diff oil performance. That 10,000cst oil that feels perfect in winter turns to water when summer hits. We actually know racers who keep different diff setups for different seasons - sounds excessive until you experience the difference yourself. A properly tuned diff in 35-degree heat versus 15-degree cold is like driving two different cars. If you're racing seriously, you need to factor in ambient temperature, not just track conditions.

Temperature Effects and Australian Climate Considerations

Let's talk about something that drives Australian RC enthusiasts mental - temperature swings. Silicone oil viscosity changes dramatically with temperature, and in a country where you can experience four seasons in one day (looking at you, Melbourne), this matters heaps. As a rough guide, oil thins by about 50% for every 20-degree temperature increase. That means your perfect winter setup will feel like you're running water in summer.

We've done some informal testing at the shop (okay, we got bored one arvo and stuck bottles in the freezer), and the difference is shocking. A 500cst oil at 10°C behaves more like 700cst, while at 40°C it's closer to 350cst. Now imagine what that does to your carefully tuned race car. This is why serious racers in Queensland run different oils than their mates in Tasmania, even on identical tracks.

The Australian summer is particularly brutal on oils. Not only does the ambient temperature affect viscosity, but the oils themselves heat up during use. After a 10-minute run in 38-degree heat, your shock oil might be approaching 50-60 degrees. Diff oils can get even hotter, especially in high-power brushless setups. We recommend going up one weight grade in summer if you're experiencing fade or inconsistent handling as sessions progress.

Storage matters too, though most people don't think about it. Keeping your oils in a hot shed versus an air-conditioned house can affect their long-term consistency. Extreme temperature cycling can cause the oil to separate or degrade faster. We store our shop stock in a temperature-controlled room, and honestly, you should at least keep your oils somewhere that doesn't turn into an oven. That garden shed that hits 50 degrees in summer? Not ideal for your expensive race oils.

Mixing Oils and Other Myths That Need to Die

Right, time to bust some myths that we hear every week at the counter. First up - mixing different weight oils to create custom viscosities. Yes, it works. No, it's not rocket science. If you mix equal parts 300cst and 500cst, you get roughly 400cst. The key word there is "roughly" - it's not perfectly linear, but close enough for RC use. We've been doing this for years when specific weights aren't available.

But here's the myth that needs to die: mixing different brands is dangerous. Unless you're mixing silicone oil with something completely different (like motor oil, which we've actually seen someone do), you're fine. All pure silicone oils are compatible. The worst that happens is slight variations in additives might change the feel slightly. That said, we still recommend sticking to one brand within a particular component for consistency.

Another pearler we hear: "You need to change shock oil every run." Absolute rubbish unless you're at professional level racing in extreme conditions. Good quality silicone oil lasts ages. For most bashers, changing shock oil every 6-12 months is plenty. Diff oil even less frequently unless you're noticing problems. The oil doesn't "wear out" like motor oil - it just gets contaminated with debris or slowly leaks out.

The "thicker is always better for beginners" myth drives us spare too. We've seen newcomers running 800cst in their shocks because someone told them it's more forgiving. Sure, it might save your suspension on bad landings, but you've also created a pogo stick that can't handle any actual track features. Start with manufacturer recommendations, then adjust based on your driving style and conditions. There's no universal "beginner weight."

Oh, and that old trick about adding a drop of dishwashing liquid to your shock oil for "better bubbles"? Please don't. Just... don't. It completely ruins the oil's properties and will probably destroy your shock seals. If you're getting air bubbles, you're either overfilling, not bleeding properly, or your seals are stuffed. Fix the actual problem instead of adding fairy liquid to expensive race oil.

Track-Specific Tuning With Oil Changes

Every track has its own personality, and oil selection is how you match it. Take our local tracks as examples - the Keysborough indoor carpet track versus the Cranbourne dirt circuit. Same 1/10 buggy class, completely different oil setups. Indoor carpet needs responsive suspension and quick diff action (300-400cst shocks, 3,000cst diffs), while the outdoor dirt with its massive jumps demands heavy damping (600cst shocks, 7,000cst diffs). Try running your carpet setup on dirt and you'll be rebuilding shocks by lunch.

High-grip versus low-grip is the fundamental decision. High-grip surfaces like fresh carpet or treated clay let you run lighter oils because the tyres aren't sliding around. The suspension can react quickly without unsettling the chassis. But on dusty, loose, or wet surfaces, you need heavier oils to slow down weight transfer and maintain stability. We've seen the same driver run anywhere from 300cst to 700cst in their shocks depending on track conditions.

Jump-heavy tracks are where oil weight really shows. Landing a triple with 300cst oil? You're gonna bottom out hard. But run 700cst on a technical, bumpy section and you'll bounce off every little imperfection. The trick is finding the sweet spot - heavy enough to soak up the big hits but light enough to handle the small stuff. Most racers compromise around 500-550cst for mixed conditions, then fine-tune with spring changes.

Here's something most people don't consider - track evolution during the day. That pristine morning surface gets rougher, dustier, and more challenging as hundreds of laps get laid down. Smart racers adjust their oil strategy accordingly. Qualify on lighter oil when the track's smooth, then bump up weight for the mains when it's chopped up. We know one bloke who keeps three sets of pre-filled shocks in different weights and swaps them between rounds. Excessive? Maybe. Fast? Definitely.

Maintenance Schedule and When to Change Your Oils

Let's be honest - most of us run our oils way longer than we should. But unlike your car that screams for an oil change every 10,000km, RC oils deteriorate quietly. Your shock oil slowly leaks past seals, gets contaminated with dirt, and breaks down from heat cycles. The first sign is usually inconsistent handling - the car feels different at the end of a run than the beginning. That's oil fade, and it's telling you something needs attention.

For the average weekend basher, here's a realistic maintenance schedule: shock oil every 6 months or 20 gallons of fuel (for nitro runners), diff oil once a year unless you notice issues. If you're racing competitively, cut those intervals in half. And if you're practicing multiple times per week? You should probably rebuild shocks monthly and check diffs every couple of months. Yes, it's a hassle, but fresh oil genuinely transforms how a car drives.

Signs your shock oil needs changing: leaking around the shaft (obviously), inconsistent damping between shocks, foamy or milky appearance when you open them up, or that horrible scratchy feeling when compressing the shaft. For diffs, listen for grinding noises, check for excessive play, or notice if one wheel spins way easier than teh others. We've opened diffs that looked like chocolate milkshakes inside - that's what happens when you ignore maintenance for two years.

The actual oil change process matters too. Don't just dump and refill - proper maintenance means cleaning everything. For shocks, disassemble completely, clean all parts with appropriate cleaners, check O-rings for damage, and replace if necessary. Let parts dry completely before reassembly. For diffs, same deal - clean out all the old oil thoroughly. That residue mixing with new oil changes the viscosity you're carefully selecting.

Storage between sessions affects oil life too. Cars sitting for months can develop problems - seals dry out, oil separates, and contamination settles. If you're pulling out a car that's been shelved for a season, at least cycle the suspension and check for smooth operation. Better yet, do a full service before expecting it to perform like it used to. We see heaps of "my car handles weird" problems that are just neglected maintenance.