⚙️ Diff Oil
The thick silicone oil inside a gear diff, rated in centistokes (cSt), which sets how much the diff resists letting one wheel spin faster than the other.
Thin oils (a few thousand cSt) let the diff act freely for easier rotation; heavy oils (30,000cSt and up) push it toward locked for more forward drive. Change one diff at a time so you can actually feel what it did.
What it actually does
In a sealed gear differential, the oil inside decides how much the diff resists letting one wheel spin faster than the other. It is one of the most powerful handling adjustments available, and one of the least visible — two identical-looking cars can drive completely differently on diff oil alone.
In practice
Thicker oil makes the diff act more locked, sending power to the wheel with grip and adding corner-exit drive and stability. Thinner oil lets the wheels differ more freely, which frees the car up to rotate. Front, center and rear diffs each change the car differently, so change one at a time.
Worth knowing
Fill to the correct level and check for leaks after a rebuild. A diff quietly leaking oil will slowly change the car's balance run by run, which is maddening to chase through setup changes.
Related terms
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