RC car tires don't utilize pressured air like real cars do. Air should be able to pass freely in and out of your tires, and even though most rim manufacturers drill holes in the rims to allow this passage of air there is a better method. Use a leather punch, side cutters, or even a high-speed moto tool to bore two holes (on opposite sides of your tire) directly into the face of the tread pattern. Try to do it in between spikes or tread so you don't remove any valuable traction-providing bits of rubber. By having holes in the actual rubber of the tire instead of (or as well as) just in the rim you allow centrifugal force to help remove dirt and moisture that may get trapped within your traction providers once they start spinning. Holes in the rubber also make it much easier to drain out any water that may get trapped when you are cleaning your tires between runs.