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Yes 33 relates to Rolling Rock but it also is the tire pressure specification for our Ascent. I would have thought that filling that 33 lbs. in the Denver area at my local Discount Tire would be a simple matter. Apparently I was wrong. If anyone has followed my previous posts on this topic, you would have read how all was well until I had my tires rotated and then my cold pressure fill up started consistently resulting in the TPMS indicating 28 to 30 lbs. Prior to that rotation, the TPMS read 32 or 33 lbs. I scratched my head for a month or so trying to figure out why this sudden change in the TPMS readings (no TPMS warning light evewr came on). My theory included maybe the technician did not properly calibrate the TPMS sensors properly after the rotation. I called around and learned nothing that was helpful in determining a cause. I even have set up an appointment for Subaru to take a look at it. Yesterday I went up to Boulder for work and stopped off at a Discount Tire for an air check and told the technician of my concern. He was willing to fill the tires and then recalibrate the TPMS. I did not have time that day so I just drove off after the fill. He set the machine at 33 so I was confident he had done his jobe properly. After a few miles, yet again the sensors read 28 lbs. Something was amiss. Today I stopped off at another Discount Tire and the technician heard my story. He stated that all the Discount Tire stores use the same machine (some are portable versions of those mounted on the wall), but all are calibrated to deliver pounds of air at SEA LEVEL. They use a chart to determine how much to add based on the elevation, which here is an additional 3lbs. If I wanted to end up with 33lbs. pressure in my tires the machine would have to be set at 36 lbs. Sure enough after he filled the tires (setting at 36) and a few miles of driving the sensors read a sweet 33. I was happy to have that mystery solved but dismayed at Discount Tires insufficient training at at least two stores over years of service. My wife's older vehicle which does not have TPMS was never being filled properly because they did not adjusted the machine setting due to the elevation. When I drive up for an air check asking for them to be filled at 33, the correct response would be an explanation that they need to set the machine at 36 due to the machine calibration at sea level. In the past years, the closest I ever heard was that they often over fill due to temperature. I never go in for an air check when tires are hot so that was never an issue. I therefore would insist on the manufacturer specification. I have used Discount Tire for decades and will continue to do so. I am simply more knowledgeable now and can, when necessary help the technicians to properly take care of my vehicles. I also hope that Discount Tires nationally addresses this training lapse at locations this may become an concern.
 

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Wow, glad you figured that out.
 

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This just sent me down a rabbit hole to find out if the TPMS re-learns the tire positions after a rotation. I have rotated my tires at home but never thought about the TPMS.

I read that the new tire postitions will learn their new positions after driving around a bit. Can anybody confirm if this is true?
 

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This just sent me down a rabbit hole to find out if the TPMS re-learns the tire positions after a rotation. I have rotated my tires at home but never thought about the TPMS.

I read that the new tire postitions will learn their new positions after driving around a bit. Can anybody confirm if this is true?
AFAIK, that's how it works.
 
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