Oxygen is actually not flammable, like NoS systems people run it their race cars. It just supplies highly concentrated oxygen into any burning environment.
You can mix it will harm nothing, the only positive about running pure nitrogen in tires is the it has zero moisture in it unlike the atmospheric air we breath, moisture expands and contracts with temperature changes. however even nitrogen will expand with enough heat, just not nearly as much.
My understanding is the nitrogen molecules are a little bigger than just "air" molecules. So, the tires don't leak as much. I keep a bottle of nitrogen at my hanger as most aircraft tires are inflated with nitrogen. Also, the nitrogen is not affected by temperature change as much as air, that's why an aircraft can descend from a high altitude to the surface and not have a problem.
Similar threads
