FRED! letting air out does NOT change the circumference...
Dia is used to acertain the circunference.. NOT height!

Correct me if I'm wrong but it doesn't letting air out of a tire affect the rolling radius of said tire and rolling radius is what calculates how many revolutions a tire makes in a certain distance?

I believe that is why locker manufactures warn people NOT to run mis-matched tire pressures on an axle with a locker installed, I know if my rear tires are 5 PSI off from each other I get a-lot of clunking and popping from my locker. Changing the rolling radius of a tire with it's inflation is more prevalent on a vehicle that has a locker so I'll use that as an example. Basically a locker effectively locks both axle shafts and thus the tires so they make the same amount of revolutions going in a straigt line in a certain distance, so having mis-matched tire pressures say 30PSI and 35PSI changes the rolling radius of the tires thus causing one tire to make more revolutions than the other in the same amount of distance going in a straigt line. So with a locker that is why a driver would notice erratic behavior because the locker is releasing the "locking" operation due to the driveline bind caused by the two different rolling radius of the tires on the same axle with different tire pressures. IF this wasn't the case then that would mean a two tires of the same size, one inflated to 5PSI and the other inflated to say 40PSI would make the same amount revolutions if they both traveled the same distance <img src="/forums/images/graemlins/confused.gif" alt="" /> . So reducing the air in the larger tire 235/70 would get it closer to the rolling radius of the smaller tire 225/70. I also stated that this would be a temporary fix for this particluar person's problem, meaning that he should not to do a 600 mile trip like this...

Fred R.