I live in Colorado Springs at 6600ft elevation. I was surprised when I discovered that the local tire repair shop had set tire pressure in my wife’s 2012 4Runner to 40psi. The rating plate calls for 32psi. When I asked about this, I was told the additional pressure is to compensate for the lower atmospheric pressure at our altitude. I then called the local Toyota dealer and was told that they do the same thing. It seems to me that what we care about is the differential pressure from inside to outside the tire, which is by definition ‘gauge’ pressure. I think tire pressure should be set to the recommendation of the manufacturer irrespective of altitude (not including possible adjustment for expected temperature variation). Am I correct?
You are correct. Gauge pressure is referenced to atmospheric pressure. I don’t know where this “old wives tale” came from but it wasn’t science!
Even this article only talks about changes in pressure as you drive from low to high altitudes and back.
https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=167
Notice in NO way would an altitude change from sea level to the Mile High City raise the internal pressure by 8 psi.
4 words:
Bo. Oh. Oh. Gus.
Yep, wrong. Take it the other way - if someone was in a super-deep canyon, would they reduce the tire pressure? Nope!
It would have made more sense if the tire shop said they put in more air to compensate for cold weather.
Ask NASA what pressure they put in the lunar rovers’ tires.