This question is answered best with an internal memo from the engineers of Honda:
Surf any automobile tire-related website these days, and you’ll likely see something mentioned about nitrogen inflation. It’s becoming a hot topic. We’ve gotten a number of inquiries lately concerning American Honda’s position on this practice. When it comes to inflating automobile tires, it’s our position that ordinary, dry-compressed air — which is about 80% nitrogen already — is the best choice. That’s because it’s more readily available, and the benefits of using nitrogen simply don’t appear to outweigh those of using compressed air. The practice of inflating tires with nitrogen really isn’t anything new; it’s been around a long time. It’s been commonly used on aerospace vehicles, commercial and military aircraft, military vehicles, race cars, and even heavy off-road construction equipment. Here’s why:

• To meet rigid safety and performance specs, the required tire inflation pressures are often very high, especially in the aerospace industry. The tire inflation pressure for NASA’s space shuttle, for instance, is a whopping 315 psi!
• Nitrogen is an inert gas; it doesn’t combust or oxidize.
• The process used to compress nitrogen excludes water vapor. Water vapor can expand if the temperature climbs above 212 degrees Farenheit
  

Tires inflated with nitrogen leak more slowly over time than those inflated with compressed air. Automobile tires, on the other hand, are subjected to an entirely different set of conditions. Here’s why inflating tires with nitrogen offers no real advantages:
When a tire is mounted on a rim the inside of the tire is full of ambient air, typically which has a high level of moisture or humidity in Ohio and the Midwest areas. Moisture is the big problem. You would need to vacuum out the ambient air and nitrogen fill the mounted tire, bleed out the mixed air and fill it again with nitrogen to have a proper nitrogen inflated tire.

• Although tires inflated with nitrogen leak slower over time than those inflated with compressed air, they still leak and need to be re-inflated periodically to maintain pressure. If you can’t find a place that offers nitrogen inflation — and there aren’t yet all that many places that do — your only option left is to re-inflate with compressed air. Doing that drops the nitrogen purity.
  
• Nitrogen offers no better protection against road hazards such as cuts and punctures. So no matter what you inflate the tire with, you still need to check the condition and pressure of the tires at least once a month as recommended in the owner’s manual.
• Tires that are inflated with compressed air and properly maintained offer the same fuel economy, tread wear, and ride comfort as those inflated with nitrogen.
  

Nitrogen for automobile tires is produced by nitrogen generators, which typically get about 95% purity. But to actually get that level of purity into an automobile tire, you would have to deflate and inflate that tire with nitrogen several times. If you’re not careful doing this repeated deflation and inflation process, the purity level winds up being closer to 90%. When compared with normal compressed air, which is about 80% nitrogen to begin with, you may start to wonder if there is any benefit at all. Because of this, those claims of less pressure loss with nitrogen aren’t valid.
 
So here’s the bottom line: Nitrogen is an ideal gas for inflating tires in aircraft, military vehicles, race cars, and heavy off-road equipment, but when it comes to automobile tires, it offers no apparent advantages over ordinary, dry-compressed air. Our advice to you: Just stick with the air you breathe!

Customers ask us all the time at Laker Tire & Service, LLC why their tires lose air pressure. The series of photos below show what a corroded aluminum rim looks like and the steps to correct and slow down the condition that causes corrosion and leaky rims.

Sometimes, customers come into our shop after having tires installed by another shop or a big box store, and the other place did not correct their rims to avoid the hassle. Many times, a customer will tell us they've had their vehicle back to the competitor's shop 2 or 3 times to correct a wheel vibration, and the problems still aren't fixed.

Here at Laker Tire & Service, LLC, we always pull the wheels and grind the mounting plates. Typically, the vibration stops immediately after taking this very necessary step that the big box stores often skip. (The top 3 photos below are the "BEFORE" photos.  The bottom 4 photos show the "AFTER" results after Laker Tire & Service, LLC took care of the problem the RIGHT WAY the FIRST TIME.

Today in the shop, we were again reminded that we do business unlike anyone else around here.  A customer came to us with new brake pads, installed by a local competitor.  Pictured below, you can see our competitor's brake pads on the left.  And on the right, are the brake pads we install on the exact same make and model vehicle.  Laker Tire & Service's new brake pads are about 50% thicker.  Our competitor's "new" brake pads are barely the same thickness as the metal shoe they sit on, meaning they'll need replaced again much sooner than our higher-quality pads. 

We aren't interested in selling and installing low-quality parts on your vehicle just to get you back in our shop spending more of your hard-earned money sooner.  That's not how we do business at Laker Tire & Service.  We do the job the RIGHT WAY the FIRST TIME.  So whether it's brakes, tires, or correcting a competitor's mistake, make sure you contact us for your next vehicle service need.