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2020 Forester Sport
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Discussion Starter #1
I set my cold tire pressures to 36psi front and 34psi rear. I drove around our housing development so I could check the tire pressure display. It showed 33psi for the fronts and 31psi for the rear tires, which is 3 psi less than what I set them. How accurate is the direct TPMS on the 2020 Forester?
 

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2019 Touring CVT
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258 Posts
My 2019 touring Foresters both are within about 1 pound of my fills. I use a digital gauge when filling. Gauges vary a lot in accuracy.
 

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2020 Forester Sport
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Discussion Starter #3
Thanks. Good to know. The gauge I use is analog, but is within 1 psi of my other tire pressure gauges, including the digital one I have. That older analog gauge comes out about in the middle, so I've stuck with it for years. Maybe when I drive the Forester farther it will display pressures closer to what I show with the gauge.
 

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2019 3.6R & 98 Forester Atlanta, GA
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2019 Forester Limited
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376 Posts
My TPMS reads within 0.5 PSI true pressure on all 4 tires, which is surprisingly good and probably not the norm. I'm fortunate to have access to a calibrated pressure source to check my gauge. I've had Autozone gauges that deviated from true pressure by +-2 psi. Agree with @SuperRu that Longacre makes a decent gauge.
 

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2019 Forester Touring CVT7
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144 Posts
TPMS is fixed to Sea Level ... most external gauges display based on your Altitude...
at 10000ft is like 4.6 psi difference
 

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2020 Forester Sport
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Discussion Starter #8
My TPMS reads within 0.5 PSI true pressure on all 4 tires, which is surprisingly good and probably not the norm. I'm fortunate to have access to a calibrated pressure source to check my gauge. I've had Autozone gauges that deviated from true pressure by +-2 psi. Agree with @SuperRu that Longacre makes a decent gauge.
That would be great to have. Where could I get access to a calibrated pressure source?
 

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2020 Forester Sport
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Discussion Starter #9
My TPMS reads within 0.5 PSI true pressure on all 4 tires, which is surprisingly good and probably not the norm. I'm fortunate to have access to a calibrated pressure source to check my gauge. I've had Autozone gauges that deviated from true pressure by +-2 psi. Agree with @SuperRu that Longacre makes a decent gauge.
That would be great to have. Where could I get access to a calibrated pressure source?
 

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2020 Forester Sport
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16 Posts
Discussion Starter #10
TPMS is fixed to Sea Level ... most external gauges display based on your Altitude...
at 10000ft is like 4.6 psi difference
We're at 2800 feet. Maybe that's the issue. I'll check more on that. Thanks.
 

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2019 Forester Limited
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376 Posts
That would be great to have. Where could I get access to a calibrated pressure source?
Where I worked had a calibration lab. Most decent sized cities will have a calibration business. Just google "pressure gauge calibration". No idea what the cost would be though. I did mine because I could, not because I thought it was critical.
 

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2019 Forester Limited
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376 Posts
TPMS is fixed to Sea Level ... most external gauges display based on your Altitude...
at 10000ft is like 4.6 psi difference
Being a sea level flatlander, I'd never thought about that.

So if fill my tires to 35 and then drive to Denver, my TPMS readout will still show 35 PSI, but my hand held pressure gauge will show around 37.
 

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2011 Forester 2.5X Automatic
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109 Posts
IMHO, this is simply more needless "technological" ******** car makers ...including Subaru ...are foisting onto the "technological cognoscenti" ...in other words, younger buyers who apparently decide how to buy a car by how much "essential" and "wow-wee" technical crap is loaded onto the car. Cup holders where a lot less expensive. This TPMS is a perfect example. In the old days people bought a tire gauge ....a good tire gauge. And they used the gauge to regularly check the pressures in their tires. They bent down, unscrewed the valve cap and mashed the gauge on the valve stem ...times four ....maybe five if they checked the spare.
And you know what?
It always worked.
And it still does today.
And it was always accurate ...or at least consistent and reliable.
But not today. Oh no ...we have "technology" to do this "dirty job" of checking our tire pressures. Except it doesn't work ....reliably and accurately. But trendy buyers can't live without this worthless garbage that does nothing but raise the price of the vehicle, make it that much more expensive to maintain and fix and make it immensely easier to total the vehicle if it's involved in an accident.
The solution to your problem?
Get a decent tire gauge and check your tires yourself and to heck with the "direct TPMS".
 

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2020 Forester Sport
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16 Posts
Discussion Starter #15

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2020 Forester Sport
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Discussion Starter #16
IMHO, this is simply more needless "technological" **** car makers ...including Subaru ...are foisting onto the "technological cognoscenti" ...in other words, younger buyers who apparently decide how to buy a car by how much "essential" and "wow-wee" technical crap is loaded onto the car. Cup holders where a lot less expensive. This TPMS is a perfect example. In the old days people bought a tire gauge ....a good tire gauge. And they used the gauge to regularly check the pressures in their tires. They bent down, unscrewed the valve cap and mashed the gauge on the valve stem ...times four ....maybe five if they checked the spare.
And you know what?
It always worked.
And it still does today.
And it was always accurate ...or at least consistent and reliable.
But not today. Oh no ...we have "technology" to do this "dirty job" of checking our tire pressures. Except it doesn't work ....reliably and accurately. But trendy buyers can't live without this worthless garbage that does nothing but raise the price of the vehicle, make it that much more expensive to maintain and fix and make it immensely easier to total the vehicle if it's involved in an accident.
The solution to your problem?
Get a decent tire gauge and check your tires yourself and to heck with the "direct TPMS".
I have neighbors who don't check their own tire pressures. For people like that, direct TPMS readings might get them to pump up the tires when they normally wouldn't .
 

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2019 Forester Limited
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376 Posts
Do you know if a liquid filled pressure gauge is affected by atmospheric pressure? If not, I think it might be worth the extra expense to get one, so that the pressure reading would be the same at any altitude.
All hand held pressure gauges, including liquid filled, are affected by atmospheric pressure. That's a good thing. They read the difference between internal tire pressure and the local atmospheric pressure. That's why a tire filled at sea level will read a higher pressure at 10,000 feet. That's a good thing, because it's the difference between the two pressures (internal and atmospheric) that dictate how firm or soft your tires are.

The liquid's purpose is to damp/slow the movement of the mechanism, protecting it against sudden shocks when you press it to the tire's valve, or hit the air bleed button.
 

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2020 Forester Sport
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Discussion Starter #18
All hand held pressure gauges, including liquid filled, are affected by atmospheric pressure. That's a good thing. They read the difference between internal tire pressure and the local atmospheric pressure. That's why a tire filled at sea level will read a higher pressure at 10,000 feet. That's a good thing, because it's the difference between the two pressures (internal and atmospheric) that dictate how firm or soft your tires are.

The liquid's purpose is to damp/slow the movement of the mechanism, protecting it against sudden shocks when you press it to the tire's valve, or hit the air bleed button.
Thanks for the info. I guess where I'm confused then, is how to know what pressure to set your tires at when you're above sea level. Are the OEM cold pressure recommendations only for at sea level, so you need to add the increase in PSI for above sea level in order to set the tires to their recommended pressure? If that makes sense.
 

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2019 Forester Limited
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376 Posts
The hand held gauge will always be correct, regardless of altitude. If you set your tires to 35 in LA and then drive to Denver, the gauge will correctly show the tire pressure as 37 (approximate). Let some air out until they’re back at 35.
 

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2020 Forester Sport
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Discussion Starter #20
The hand held gauge will always be correct, regardless of altitude. If you set your tires to 35 in LA and then drive to Denver, the gauge will correctly show the tire pressure as 37 (approximate). Let some air out until they’re back at 35.
In your example, wouldn’t you need to leave the pressure at 37 psi, if the OEM pressure is supposed to be 35?
 
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