It can be frustrating when good science gets mixed up with poor communication. As an employee of a tire manufacturer, I have closely monitored the articles regarding nitrogen inflation of tires. Like most C&EN readers, I, too, have laughed and shuddered at the claims (predominantly by people outside of the tire industry) about how, because nitrogen is heavier, or bigger, than oxygen, it will leak out more slowly.
Nonetheless, there are real benefits to the use of nitrogen inflation. The main problem is when people (usually nonscientists) confuse the ideas of gases "leaking" and those gases "permeating" or "diffusing." As most scientists understand, all gases will escape a "real leak" in a tire at the same rate. But without a leak, these gases will also diffuse through the tire at different rates. Inflating a tire with nitrogen will slow pressure loss due to permeation by about 40%. That is, your tire will maintain its air pressure better, and proper air pressure will increase tire performance, safety, and gas mileage.
Second, nitrogen gas is usually very dry, and tires do not like internal water vapor. Water vapor in the tire causes fluctuations in air pressure with temperature changes, therefore making it more difficult to maintain the optimum, manufacturer-recommended pressure.
Third, inflating your tires with nitrogen reduces the rate of thermo-oxidative processes, which can cause degradation of rubber properties over time. Though ordinary air is mostly (approximately 78%) nitrogen, it is the 21% of oxygen that can react with the rubber as it diffuses through it. Of course, most tires are designed to operate just fine with air inflation, but inflating your tires with nitrogen can definitely improve your tire life and performance.