This is just my opinion. Any car, nitro or electric, that is raced or bashed outside should have their bearings relubed with grease instead of light oil. The surplus grease in a bearing will form a ridge on the inside of the shields, and dirt or pebbles that do get in the bearing will be trapped in that ridge of grease. This ridge of grease will hold those debris, keeping them from getting in the balls too often and wrecking havock inside the bearing. With light oil, the dirt and pebbles float free inside the bearing and just keep on scratching the balls. Don't let pebbles scratch your balls guys, use grease if you're going to play outside.