The practice/concept of filling street car tires (tires that are driven on city streets) with nitrogen has been around for the last few years. The idea has its foundation in the racing industry where nitrogen has been used to fill race tires and run air tools for decades.

What is good for race cars must be good for street cars, right? Not so fast! There are reasons why nitrogen is used in the racing industry that do not transfer to everyday, street-driven vehicles.:

1. The nitrogen molecule is larger than the mixture of molecules in regular air. Race tires are purposely built for adhesion and not for longevity, so must be as light as possible. Therefore, the race tire sidewall is not as thick and durable as on street tires. In short, race tires do not do a good job of holding inflation for long periods of time. They tend to go flat within weeks. Thus, the larger nitrogen molecules help them stay inflated longer. Street tires are very durable, and hold inflation quite well, so there is no real need for the larger molecules. Cheap street tires leak more air than good quality street tires, however, so it is important to buy good quality tires.

2. Nitrogen gas is much dryer than regular air. Race tires go through very large changes in temperatures (from 75 to 350). No street-driven tires go through such a large change in temperature unless they are severely under-inflated or being driven illegally.

3. The more moisture inside a tire, the more this affects pressure changes and tire stability. Race tires want stability, and will notice a 1 to 2 PSI (pounds per square inch) change in tire pressure. Street tires, if driven within the law, will not notice even a 3 to 4 PSI change. Also, the racing industry uses cylinders of 100% nitrogen. The nitrogen being put into street tires is NOT 100%.

So, what is all the talk on the internet about the benefits of nitrogen? Well under laboratory testing using nitrogen versus regular air, benefits to using nitrogen probably can be measured. Strict testing in a laboratory, however, is no comparison to the real world. In the real world, street tires are filled with something less than 100% nitrogen. The tire/wheel assembly already has regular air in it. This combination of air already present in the tire and the less than 100% nitrogen, further dilutes the percentage of nitrogen in the tire/wheel assembly. This dilution is enough to negate any possible positive effects from using the nitrogen.

The benefits of putting nitrogen in your normal street tires are negligible, so even if you choose to do so, do not pay to have nitrogen put in your tires. The only winner there is the facility selling the nitrogen.

Donna McCord, Owner
Dean’s Automotive, Inc.
650-961-0302
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