This is slightly off topic but I have searched the web in vain. I am trying to find air retention standards for passenger car tires. That is, what is the industry standard for air pressure loss expressed in pounds over time or miles on a sound rim? I have tried the NHTSA site and found a reference to CFR title 49 parts 400-999 but before I hit the pavement to the law library, I want to know if that fact is even included. Also reference to NHTSA standard 109. I have 4 identical tires, one of which loses 2.5 lbs after about 250 miles. Static test in water tank is negative - no leak, and of course, no nails or repaired punctures, stem and valve were replaced etc. I use a digital guage and check cold in the morning. Tire rep says that loss is "normal". I told him to wipe his mouth - there was still a tiny bit of BS around his lips...