In an RC car, shock absorbers (or shocks) are a crucial component that helps to absorb the impacts and vibrations from bumps, jumps, and other obstacles on the track. Shock oil is used to fill the shocks and to provide damping resistance to the suspension system.

The purpose of shock oil is to slow down the movement of the shock piston inside the shock body. The oil resists the flow of the piston through the shock, which in turn slows down the compression and rebound of the suspension system. The thicker the shock oil, the more resistance it provides, and the slower the suspension moves.

The oil's viscosity, or thickness, is measured in weight, such as 30-weight, 40-weight, or 50-weight, with higher numbers indicating thicker oil. The weight of the oil used in an RC car depends on various factors, such as the weight of the car, the terrain, and the driving style.

For example, if you're driving on a bumpy track, you might want to use a thicker shock oil to absorb the impacts and provide better stability. Thicker oil will slow down the suspension movement and reduce the amount of bouncing and rolling of the car. However, if you're driving on a smoother track, you might want to use a thinner shock oil to provide more responsive handling.

It's essential to use the correct weight of shock oil for your RC car to get the best performance and handling. Changing the shock oil can also be an effective way to fine-tune the suspension system to suit different track conditions or driving styles.