I would really like some help with something that is driving me absolutely crazy. It's essentially two related questions.
I use an after market TPMS for the tires on my truck and my 5er. I want to set the alarm thresholds on the TPMS for low and high pressure for all the tires, and I know what the cold pressure is supposed to be for each set of tires, but I have no way of reading the tire pressure on the tires that I can trust. I have 4 different pressure gauges in addition to the TPMs, and every one of them gives me a different pressure reading from each other, and some of the variances are as much as 10psi. None of the gauges have any kind of calibration option, but even if I picked just one of them and was willing to do the math in my head, I still need to know by how many psi that particular gauge is wrong.
This is maddening. So my first question is, how does anyone know if the tool they are using to measure psi is accurate? The TPMS has a feature that allows me to calibrate it to compensate, but I need a starting point I can trust in order to do that.
And the second question (which supposes I can solve this first problem) is, how much spread should there be between the low and high pressure alarms on the TPMS? I am routinely seeing a 30+ psi change between cold pressure in the morning before I start driving, and later in the afternoon. That seems pretty high, but I don't know for sure. I'm sure it's due to the fact that if I start out cold and it's 34° and at 4pm it's 80°, but I'd like to know for sure that that's OK. When we were weighed we were told what the cold psi should be, but not what an acceptable hot psi is. The same goes for temperature. I have no idea what the high temp warning setting should be. At the moment, the alarms are going off pretty much all the time, and I want to correct this before I get in the habit of just ignoring the TPMS, which sort of defeats the purpose of having it in the first place.
Lee
-- Edited by Camper Chronicles on Tuesday 20th of September 2016 10:02:21 AM
RonC said
10:32 AM Sep 20, 2016
I have a Viair RV air compressor which has a trigger handle with a gauge ... which is what I use and assume that it's accurate ... but certainly not guaranteed. It does agree with my TST 507 TPMS so at least they validate each other. TST recommends the alarms be set at 10 psi below and 20 psi above the cold pressure settings. So a 30 psi rise would cause a pressure alarm, assuming you start out at the correct cold pressure setting. When you start out at 34 degrees ambient, is your cold pressure set correctly? I ask, because if you start out under inflated then you will generate additional heat and pressure. I typically see tire pressures running about 15 psi over my cold pressure. My tires are set at 105 psi cold so I see 120 or so during the heat of the day at highway speeds. With regard to your questions about tire temperature ... TST recommends setting the alarm at 158 degrees. They say that temperature related blow outs occur between 180 and 200 degrees. My tires seldom see any thing higher than 20 degrees over outside temperature, but have occasionally gone up to 25 or 30 if the sun is shining hard on one side. I have never had a temperature or pressure alarm using these settings.
-- Edited by RonC on Wednesday 21st of September 2016 04:14:15 PM
Clay L said
11:28 AM Sep 21, 2016
At a rally Michelin had a big tire/wheel filled with air and a tire gauge that was calibrated and certified. They would check your gauge against the tire. The problem is getting access to a calibrated/certified gauge. Suspect they are expensive. I found this one HERE and as you can see it is expensive - $299.
-- Edited by Clay L on Wednesday 21st of September 2016 11:28:56 AM
RonC said
04:16 PM Sep 21, 2016
That's a pretty expensive tire gauge alright. I doubt I'll ever own one of those.
Rickl said
11:01 PM Sep 21, 2016
Most quality tire shops have a "master" gauge and would check your gauge for accuracy. If your present shop doesn't have one I would run! The other thing you can do is check your gauges pressure reading against 3-4 others on the same tire. A large truck tire will suffice as opposed to a smaller tire with less volume. If all 3-4 are within 1psi then you can safely assume the accuracy.
MarkS said
01:32 AM Sep 22, 2016
Accuracy is always nice and I would look for a way to confirm the accuracy of my gauge but, I wouldn't loose any sleep in the meantime. If you are within 10 pounds and checking with a gauge you are already doing more than most. Do the best you can, set up your TPMS, continue to look for a way to check your gauge for calibration. You deserve a medal for caring in the first place.
CJSX2fromCT said
02:17 AM Sep 22, 2016
Great question Lee, I do 2 things. I set my air compressor gauge (output) to 80 lbs for the truck and 100 lbs(G114's) for the trl. I then check with only one air pressure gauge. (Heavy Duty Straight Foot Dual Head) I "use" to check it with multiple gauges and like you got different readings. My left rear trl tire runs higher pressure and hotter then the other 3 I have noticed, so what I do is I drop that one down 5psi knowing it will gain it back and it does while running. I believe it is on account that is the side our kitchen is on. I have my monitor set at 100psi for low and 125psi for high, at this time I am only running sensors on the trl. Hope this helps you. Safe travels ahead.
Rickl said
12:29 PM Sep 22, 2016
10 psi can mean a significant amount of carrying capacity depending on the size of the tire. Be cautious. Also, you should always set tire pressures when the tire is "cold". That means that the tire hasn't been run and is sitting at ambient air temperature. Once set leave the pressure alone during the day. Yes you may see an increase as the temp warms up and depending on the static load the tire/wheel assembly is being asked to haul.
That is why it is so important to KNOW your individual wheel position weights. Don't panic if you get an increase in pressure that stabilizes. However if you are driving and the pressure spikes it is a good indication that you probably overloaded as a result of loss of pressure.
When you get a leak the pressure will drop obviously, but continued driving heats the tire up increasing the pressure. At that point two things can occur, first a "blowout" as the pressure generated finally exceeds the limit of the tire of your tire is so hot it starts to delaminate. Delamination is essentially reversing the vulcanizing process of the tire. Those are the pieces you see on the side of the highway.
I would really like some help with something that is driving me absolutely crazy. It's essentially two related questions.
I use an after market TPMS for the tires on my truck and my 5er. I want to set the alarm thresholds on the TPMS for low and high pressure for all the tires, and I know what the cold pressure is supposed to be for each set of tires, but I have no way of reading the tire pressure on the tires that I can trust. I have 4 different pressure gauges in addition to the TPMs, and every one of them gives me a different pressure reading from each other, and some of the variances are as much as 10psi. None of the gauges have any kind of calibration option, but even if I picked just one of them and was willing to do the math in my head, I still need to know by how many psi that particular gauge is wrong.
This is maddening. So my first question is, how does anyone know if the tool they are using to measure psi is accurate? The TPMS has a feature that allows me to calibrate it to compensate, but I need a starting point I can trust in order to do that.
And the second question (which supposes I can solve this first problem) is, how much spread should there be between the low and high pressure alarms on the TPMS? I am routinely seeing a 30+ psi change between cold pressure in the morning before I start driving, and later in the afternoon. That seems pretty high, but I don't know for sure. I'm sure it's due to the fact that if I start out cold and it's 34° and at 4pm it's 80°, but I'd like to know for sure that that's OK. When we were weighed we were told what the cold psi should be, but not what an acceptable hot psi is. The same goes for temperature. I have no idea what the high temp warning setting should be. At the moment, the alarms are going off pretty much all the time, and I want to correct this before I get in the habit of just ignoring the TPMS, which sort of defeats the purpose of having it in the first place.
Lee
-- Edited by Camper Chronicles on Tuesday 20th of September 2016 10:02:21 AM
I have a Viair RV air compressor which has a trigger handle with a gauge ... which is what I use and assume that it's accurate ... but certainly not guaranteed. It does agree with my TST 507 TPMS so at least they validate each other. TST recommends the alarms be set at 10 psi below and 20 psi above the cold pressure settings. So a 30 psi rise would cause a pressure alarm, assuming you start out at the correct cold pressure setting. When you start out at 34 degrees ambient, is your cold pressure set correctly? I ask, because if you start out under inflated then you will generate additional heat and pressure. I typically see tire pressures running about 15 psi over my cold pressure. My tires are set at 105 psi cold so I see 120 or so during the heat of the day at highway speeds. With regard to your questions about tire temperature ... TST recommends setting the alarm at 158 degrees. They say that temperature related blow outs occur between 180 and 200 degrees. My tires seldom see any thing higher than 20 degrees over outside temperature, but have occasionally gone up to 25 or 30 if the sun is shining hard on one side. I have never had a temperature or pressure alarm using these settings.
-- Edited by RonC on Wednesday 21st of September 2016 04:14:15 PM
At a rally Michelin had a big tire/wheel filled with air and a tire gauge that was calibrated and certified. They would check your gauge against the tire. The problem is getting access to a calibrated/certified gauge. Suspect they are expensive.
I found this one HERE and as you can see it is expensive - $299.
-- Edited by Clay L on Wednesday 21st of September 2016 11:28:56 AM
That is why it is so important to KNOW your individual wheel position weights. Don't panic if you get an increase in pressure that stabilizes. However if you are driving and the pressure spikes it is a good indication that you probably overloaded as a result of loss of pressure.
When you get a leak the pressure will drop obviously, but continued driving heats the tire up increasing the pressure. At that point two things can occur, first a "blowout" as the pressure generated finally exceeds the limit of the tire of your tire is so hot it starts to delaminate. Delamination is essentially reversing the vulcanizing process of the tire. Those are the pieces you see on the side of the highway.