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Old 08-23-2016, 03:05 PM   #1
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Tpms accuracy

I have the TST 507 TPMS. When I set it up I aired the tires to 65 psi. I did this at noon because this is when we usually leave on a trip. In checking the PSI's today I have two tires at 65, one @ 66, and one@ 63. I checked the two giving different reading with two brand new gauges and the 63 is @ 66 on the gauge and the 66 is @ 70 PSI. I'm very picky about tire pressures and wonder if this is normal. The book says 1.5 +,-. I understand ambient temps will cause increases and decrease's. My concern is that the sensors and my gauges are that far off.
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Old 08-23-2016, 08:41 PM   #2
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I, like you, notice fluctuations in most tire gages. I have used digital and moving rod pressure gages, they all read differently sometimes. Some are way off, and I toss those in the round file. I account for ambient air temps, and sunlight beaming on the tires that will elevate the readings.
Now I just measure them in the AM when its cool, use the TPMS as the baseline for accuracy, and not worry about it anymore. As your tires travel down the road, the pressures can go up 5-6 degrees.
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Old 08-24-2016, 07:15 AM   #3
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All four of my 507 sensors were nearly perfect using a good digital gage. When I needed to replace a broken sensor, the new one reads 2 pounds lower. Not a big deal, just write down error and sensor number for reference.
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Old 08-24-2016, 07:26 AM   #4
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Remember, if your TPMS is off 1-2 lbs. in one direction and your gauge is off 1-2 lbs. in the other, it's a total of 2-4 lbs. difference. The TPMS is a "monitoring" system and used to warn of a major impending situation possibly upcoming. A sudden loss of pressure or slow leak which shows a 15-20 psi loss over time.
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Old 08-24-2016, 07:49 AM   #5
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TPMS systems are not for individuals with persnickety personalities. It will usually drive them crazy!

TPMS systems are to warn you of slow or fast leaks in your tires. It is NOT used to give you the precise psi readings that an expensive calibrated tire pressure gauge is designed and used for accomplishing that task.

Under-inflation of a tire is DEATH to that tire. That's why the LOW PSI alarm setting is SO important versus the over-inflation alarm setting.

But it is still only a relative setting versus actual.

Your tire pressure gauge is what should be used to set the actual CIP settings, not your TPMS.

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Old 08-24-2016, 07:51 AM   #6
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A tire expert's blog on gauge accuracy.
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Old 08-24-2016, 10:21 AM   #7
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Thanks guy's. I get the idea. Worry more about the gauge as opposed to the TPMS. It makes sense. As far as driving me crazy? Very short drive. More of a casual walk. Thanks again. Getting ready to head out for the weekend. Gonna be a hot one.
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Old 08-24-2016, 11:33 AM   #8
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Use the TPMS system more as an alert to loss of pressure during the trip, and not a scientific measurement of your tire pressure. What really matters is that if the pressure drops below a certain pressure, or loses air fast, you need to know that, not exactly what your tire pressure is when you hook up in the morning or if the pressures on your gauge exactly match up with the TPMS, which I check with a stick gauge before driving off anyways.
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Old 08-24-2016, 11:54 AM   #9
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Quote:
Originally Posted by stormrider15 View Post
My concern is that the sensors and my gauges are that far off.
I agree with the others, "A man with one watch always knows what time it is. A man with two watches is never sure."

Other TPMS idiosyncrasies:
1) Temperature sent from the external sensors is much different than the temperature sent by the in-tire sensors.
2) If you unhook your trailer the monitor in the motorhome doesn't notice it is missing for 10 minutes or more.
3) Why does the TPMS say the right side of the coach is warmer than the left? This occurs even when it's in the shade. But not when parked.
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Old 08-24-2016, 12:58 PM   #10
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Does reading the pressure through a flow-through sensor of a TPMS impact the accuracy of the reading? Or do I need to remove the TPMS sensor to get a true reading?
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Old 08-24-2016, 02:52 PM   #11
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I don't like or use them as they are too large and cumbersome to use.

Someone that's owns them and has experience with taking psi readings with and without them will have to chime in as to your question.

I use small CAP sensor on all of my vehicles.

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Old 08-24-2016, 03:54 PM   #12
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Quote:
Originally Posted by stormrider15 View Post
I have the TST 507 TPMS. When I set it up I aired the tires to 65 psi. I did this at noon because this is when we usually leave on a trip. In checking the PSI's today I have two tires at 65, one @ 66, and one@ 63. I checked the two giving different reading with two brand new gauges and the 63 is @ 66 on the gauge and the 66 is @ 70 PSI. I'm very picky about tire pressures and wonder if this is normal. The book says 1.5 +,-. I understand ambient temps will cause increases and decrease's. My concern is that the sensors and my gauges are that far off.
In the factory we knew gage accuracy as GRR. Gage reliability and repeatability. To qualify a gage for manufacturing was a long drawn out process consisting of specific trials and tests. To start with, the gage had to be capable of reading 1/10 of the characteristics tolerance. And then, 3 operators had to do the same measurement 30 times and get the same readings (statically speaking) or the gage was no good. I am not sure that a tire gage that meets that criteria exists.

So what is the tolerance on tire air pressure? plus or minus a tenth? a pound?

So you fill your tires to 95 psi and the next day they are all different by 2 pounds. It can not really matter to the tire. Within the tolerance they are all the same. Tire monitors are to let you know if anything really bad is happening to the tire not as a "accurate pressure" device.
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Old 08-24-2016, 04:10 PM   #13
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Anyone have a good tire gauge they could recommend? My current analog dial gauge only goes to 60 psi which works for my current C rated tires at 50psi, however I plan on upgrading next season to D's with 65 psi. I don't care for the pen style gauges and most of the digital gauges I see on Amazon are clearly made by the same company (exact same design with just different colors and labels) and appear to be cheap Chinese quality as they have pretty spotty reviews. Majority of the good reviews appear to be people using them a couple times a year on their 35psi passenger car tires so I take those reviews with a grain of salt.
I prefer an analog dial gauge but willing to go digital if someone has one they've had good luck with.
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Old 08-24-2016, 04:31 PM   #14
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Anyone have a good tire gauge they could recommend?

I prefer an analog dial gauge but willing to go digital if someone has one they've had good luck with.
I own THIS digital Tire Gauge and will not use anything else. It comes in its own case so it doesn't get banged around and has always been right on when checked at the local truck tire shop with their calibrated gauge.

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