The use of nitrogen gas for inflating vehicle tires has become a common practice offered by many dealerships and tire service centers. This process involves filling tires with gas that is typically 93% to 95% pure nitrogen, rather than the standard compressed air found at most gas stations. Since compressed air is already about 78% nitrogen, the goal of this service is to significantly increase the purity level by removing oxygen, moisture, and other trace gases. Drivers who have purchased a vehicle or tires with this service often need to confirm if their tires contain this specialized gas.
Checking for Nitrogen: Visual Clues and Markings
The most common indicator that a tire is filled with nitrogen is the presence of a green valve stem cap. This color-coding is an industry-wide practice intended to signal to technicians and drivers that the tire contains high-purity nitrogen instead of regular air. While this is a widely accepted standard, it is not a legal requirement, and the cap can be easily replaced or lost, making it an unreliable guarantee of the tire’s contents.
Drivers should also look for small stickers or decals placed near the valve stem on the wheel, which some service providers use to mark a nitrogen fill. Another place to check is the vehicle’s documentation, such as the original purchase agreement or recent maintenance invoices. Nitrogen filling is often an add-on service, and the paperwork should list it if the service was performed. These visual and documentary clues serve as initial indicators, but they do not provide a definitive confirmation of the gas purity level inside the tire.
The Only Way to Be Sure: Using a Specialized Analyzer
The only way to definitively confirm the gas content of a tire is by using a specialized nitrogen purity analyzer, sometimes referred to as an oxygen sensor. This handheld electronic device measures the exact percentage of nitrogen or oxygen present in the tire’s internal atmosphere. The analyzer connects to the valve stem and provides a digital readout of the gas composition within seconds.
For the benefits of nitrogen to be present, the purity level must be maintained above 93%. Since the average driver does not own this professional-grade equipment, the most reliable method is to visit a tire shop, dealership, or service center that offers nitrogen service. These locations have the necessary tools to perform a quick and accurate purity check, confirming whether the benefits of the specialized gas are still present.
Understanding the Difference: Nitrogen vs. Compressed Air
The reason for using high-purity nitrogen centers on the molecular differences between the gases. Standard compressed air contains approximately 21% oxygen and a variable amount of moisture, both of which are detrimental to tire performance and longevity. Nitrogen is an inert, dry gas, meaning it is non-reactive and contains virtually no moisture.
The moisture in compressed air causes pressure fluctuations as the tire heats up and cools down during driving, leading to less stable inflation pressure. Furthermore, oxygen molecules are slightly smaller than nitrogen molecules, allowing them to permeate, or leak, through the tire’s rubber walls at a faster rate. This difference in molecular size means nitrogen-filled tires maintain their set pressure for a longer period of time. Removing oxygen also reduces the rate of internal rubber oxidation and corrosion of the wheel rim and the Tire Pressure Monitoring System (TPMS) sensors.
Maintaining Nitrogen Tire Pressure
Regardless of the gas used, maintaining the correct inflation pressure is the most important factor for tire safety and performance. Even nitrogen-filled tires will lose pressure over time, making monthly pressure checks necessary. If a tire is low and a nitrogen source is not immediately available, it is always better to top it off with regular compressed air than to drive on an underinflated tire.
Adding compressed air to a nitrogen-filled tire is safe and will not cause any adverse chemical reaction. However, doing so will dilute the nitrogen purity, which reduces the benefits of pressure stability and reduced oxidation. To maintain the high purity level, the best practice is to return to a service provider that offers nitrogen top-offs. Many service centers provide this top-off service for free or at a low cost to customers who initially purchased the nitrogen fill.