Let us talk about tires and valves, both of which are made of rubber. There are gaps between rubber molecules, and the tire is a composite structure with steel wires and cord wiring layers and airtight layers in the middle, which are tightly combined, but there are still gaps.
Besides, the tire and wheel hub are also not completely sealed. There still may have gap between rubber and metal.
Finally, let’s talk about the wheels, most of the wheels are aluminum alloy casting and aluminum alloy forging. There are also iron wheels. The paint spraying process and subsequent corrosion will cause air leakage. There are also gaps between metal molecules.
Last but not least, give a piece of advice. Pay attention to installing tires. The lubricant used for lubrication must be a neutral one, which will not corrode tires and wheels. Furthermore, it is best to use nitrogen as the filling gas. If the air pump does not discharge water for a long time in the compressed air, and there is no effective oil-water separation, there will be a large amount of water in the tire when it is filled. The same will corrode tires and wheels.