Mixing nitrogen and air in tires reduces the benefits associated with filling tires with pure nitrogen, but is otherwise perfectly safe. Mixing air and nitrogen is preferable to driving on tires that are not properly inflated, according to Tire Rack, a tire retailer.
Air is composed of 78 percent nitrogen, 21 percent oxygen and one percent other gases. This means that, even when regular compressed air is used, the gas inside a tire is mostly nitrogen. According to the Get Nitrogen Institute, filling tires with almost pure nitrogen improves fuel economy, increases tire life and leads to better handling. However, a report by Edmunds Inc. suggests the benefits of nitrogen in tires may be overstated.