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2012 Forester XT Automatic
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14 Posts
Discussion Starter · #1 ·
2012 XT TPMS light on if any less than 36 -37 psi. Dealer and subby CS tell me normal because car is at 9000 feet. Door jamb says 30 and 32. Is this normal?? If controller looking for 32 psi and I have them at 32 psi cold, does it matter that car is at 9000 feet?
 

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2015 Highlander AWD XLE 6AT
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4,255 Posts
Everything else being equal, ambient air pressure at 9K feet is ~10.5 psi vs ~14.7 psi at sea level. Using a mechanical tire pressure gauge, I would expect it to read about 4 psi high at 9K feet.

The TMPS system triggers at ~26 psi cold, or perhaps ~30 psi cold indicated at 9K feet. If it's triggering at ~36 psi cold, then I'd try checking the tires with another gauge before taking aim at the TPMS.

HTH,
Jim / crewzer
 

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2012 Forester XT Automatic
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14 Posts
Discussion Starter · #3 ·
altitude affect

Wouldn't taking a tire with 30 psi at sea level and bringing it to 9000 feet altitude cause the pressure in the tire to drop not raise because of less atmospheric pressure against the outside of tire?

Either way, if I set my tires to the door jamb spec, in this case 32 and 30, when it is cold and at my 9000 foot altitude shouldn't the tpms light stay off?

Isn't the controller looking for a signal from the sensor that is derived from PSI Gauge?

Appreciate the help so I know if I am asking for something beyond the design. Reason I do not like to run the higher pressure is we think we get less traction and rougher ride than another Subaru we had with similar size and type tires. We are in snow a lot and use blizzak w70 tires and this one slides all over.
 

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2012 Forester XT Automatic
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14 Posts
Discussion Starter · #5 ·
sea leave verification anyone?

Car was at dealer again for this and hard brake pedal - see other post.

Dealer at 9000 feet and dealers in Denver at 5000 feet tell me it is known problem with all manuf of tpms. They set tires at 38 psi. I can get away with 36 - 37 verified with 3 gauges. Our dealer told us there was bulletin stating had to run 40 psi and was going to give us a hard copy of it, then backed out. Same for our hard brake. Subby CS says no bulletin and playing phone tag to pursue further.

Anyone at or near sea level and have problems? Verify sea level cars can run 30 and 32 psi per door jamb and manual?

My gravel roads and high pressure hammer the car and we slide around in snow noticeable more compared to our 03 forester with same blizzaks, both 16 inch.
 

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2015 Highlander AWD XLE 6AT
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I had my "sea level" '09 Forester up to 11K feet in Colorado without any TPMS issues; the tires were likely set at 34 psi at near-sea level at the beginning of the trip.

HTH,
Jim / crewzer
 

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2013 Forester Limited auto
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41 Posts
Think of it like this:
- tire pressure is recommended to be set at 32 psi to handle the weight of the car at sea level
- a tire gauge measures pressure inside of the tire RELATIVE TO air pressure outside of tire
- air pressure decreases with altitude
- weight of car remains the same at a higher altitude

so, as measured by tire gauge, you need to run a higher tire pressure at altitude for the tire to properly handle the weight of the car as it would at sea level.:icon_confused:

In other words, if you want to run the tire pressure recommended by the manufacturer, you would inflate your tires to 32psi at sea level and then drive to 10,000 ft elevation. Then, check the tire pressure. It would read 37psi (or something close to that). So, at 10,000 ft elevation, 37psi is actually the recommended pressure.

I hope I'm right, but I think I have the right idea.
 

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My10 Forester Diesel
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To maintain the stiffness of the tire you would need to let pressure out as you increased in height and re inflate as you descended. Most applications and altitude changes are not that extreme that this matters.
 
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