Diff Oil
Different Differential oils provide different performance characteristics in your RC car. These characteristics can be controlled by the different weights of oil placed in to the differential. The weight of a differential fluid is determined by the viscosity of the fluid.
Shock Oil
Pick the thicker oil for higher traction and thinner for lower traction. Thinner oil improves grip on slippery track while steering becomes lazier. Thicker oil makes steering faster and more accurate.