Shock oil is the silicone fluid inside your shock absorbers. Its thickness (weight) controls how fast the shock compresses and rebounds, which changes how the car handles. Thicker oil slows the shocks down, thinner speeds them up.

Diff oil is the silicone fluid inside a differential. Its thickness controls how freely the diff lets the wheels turn at different speeds. Thicker oil tightens the diff for more traction on power, thinner frees it up for easier turning.

It depends on how hard you run. Racers often refresh shock and diff oil every few race days to keep handling consistent. For casual bashing, change it if the car starts to feel different or the oil has gone dark or thin.

Oil is rated by weight, shown as wt or cSt (centistokes). A higher number means thicker oil. Setups usually list a target weight, so match the number, but stick to one brand where you can, since scales differ slightly between makers.

Use a thin CA (cyanoacrylate) glue made for RC tyres. It wicks into the bead and bonds the tyre to the wheel. Clean both surfaces first, apply a small bead, and hold until set for a strong, lasting join.