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Old 12-04-2013, 10:26 AM   #1
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TST TPMS Question

I recently purchased a TST TPMS, mostly because of the recommendations I saw on this forum. I have one question about the operation, the correlation between the pressure and temperature increase of the tires.

After a several hour drive I had an average (I checked all the tires individually and averaged the results of the 6 tires to make comparison easier) pressure increase of 12 pounds and a temperature increase of 16 degrees on each tire. The TPMS temperature reading although increasing 16 degrees from that at time of departure was actually reading only 6 degrees higher then ambient temperature when checked hot leading me to believe that the TPMS is reading ambient and asphalt radiated temperature instead of internal air temperature. To further check, at the same time, I checked the actual inner sidewall temperature with a digital thermometer and the temperature was an average of 32 degrees higher then displayed on the TPMS.
I have been in contact with TST and returned the system to them to be checked and they advise that it is working correctly.

Have any of you with a TPMS system recorded pressure and temperature increases and any correlation between temperature and pressure increase that I can use for comparison? Thanks in advance.
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Old 12-04-2013, 11:35 AM   #2
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Don't forget that the outer sensors are flying around in the breeze. This is a useless feature and you can simply check yours at a stretch stop with a hand held IR device.

I gave up on my TST system after they had to get cut off the valve stems due to corrosion. I use a Dual Dynamics Cross fire, and IR gauge and a pressure gauge at every stop.
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Old 12-04-2013, 11:43 AM   #3
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"The TPMS temperature reading although increasing 16 degrees from that at time of departure was actually reading only 6 degrees" How did you verify that reading?
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Old 12-04-2013, 11:58 AM   #4
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I have stated this numerous times on a variety of TPMS threads that the temperature portion of the sensor should ONLY be used as a differential comparison between tires to alert you to one that is way above the others for whatever reason.

That should raise a flag to check why that one tire is higher than the rest.

There is NO way that a sensor flying around on the outside of the stem can report an accurate temperature of the tire sidewall, thread or for that matter any part of the tire.

Also, most TPMS's will not reflect the calibrated actual PSI you have in each tire as measure with an excellent calibrated PSI gauge. Again, it should only be used as comparison between other tires on the SAME side of the coach.

Get yourself a good PSI Gauge such as this one.

Amazon.com: Accutire MS-5515B Truck and RV Digital Tire Gauge with LED Light and Bleed Button: Automotive

And also have a good Laser Guided IR Temperature gun to measure the sidewall of each tire approximately 2-3 inches from the thread and also the measure the wheel hub to check the condition of the wheel bearings.

Mastercool MSC52224A Non-Contact Infrared Thermometer with Laser : Amazon.com : Automotive

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Old 12-04-2013, 12:23 PM   #5
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I disagree that the temp feature is useless if used as Dr4Film suggests. Tire comparison is the measurement I care about and it has worked very well the last 3yrs. After losing a front tire to a LARGE pothole this past trip the TST alerted me very quickly of the flat on the front of our toad. It is not measuring on a perfect scientific scale but alerting the operator to major fluctuations.
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Old 12-04-2013, 01:55 PM   #6
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Agree with the comments of readings from a TPMS should not be taken as gospel, rather comparative and for warning of major fluctuation indicative of pending failure. They work fine when used as intended and are a valuable addition to an RV setup.
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Old 12-04-2013, 02:07 PM   #7
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Coming down mountains out west last year my TST let me know that I was using the brakes too much with an overtemp alert.
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Old 12-07-2013, 09:36 PM   #8
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I am going to agree with DR4Film on this one. I don't really care what the temps or pressure readings are. I check the tires on a regular basis with a guage. I do not worry about the accuracy of the temp. I am of the opinion and if I am wrong I am sure someone will correct me. If you have a problem with a tire such as an internal crack or weak sidewall that the tire will flex more. The additional flexing will show up as a significant heat rise. I am monitoring the tires for significant differences of heat. The same for the pressure. I know what the tires are from the manual gauge. I know tire pressures go up as the tires heat up. I watch for tire pressures to go down. I had a tire that would lose about 5 pounds a week. I was on a trip and did not want to stop and get it fixed so I made sure to add air a couple of pounds a week. When I got home I had the tire shop that had installed my tires repair it. With the tpms system I could make sure that the leak did not increase on the trip. I believe if you want to have accurate tire measurements for pressure get one of the tpms systmes that mount inside the tire. I know the ones I have on automobiles are pretty accurate.
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Old 12-08-2013, 08:59 AM   #9
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One thing that has not been mentioned that is very important.

The TST monitor only receives info and does not transmit. The sensors send info about every two minutes to the monitor unless there is a radical change, then it will transmit the problem such as leaking etc.

But and this is a big but, what if the sensor malfunctions and does not transmit any more???

What happens is the monitor will display the last known reading and hold it until it receives another transmission from the sensor. In other words the reading on the display will not change until until it receives updated info.

My monitor will not alarm if it has not received a transmission from a tire in longer than 2 minute time frame. It simply displays last known info.

The way I found this out was after disconnecting the toad one day, DW drove to the store miles away and the toad readings remained frozen on the display. When she returned the frozen readings started updating again. Try it when you disconnect.

So because of this problem I monitor temps more closely because when everything is stable on the road such as speed and outside air temp the pressures don't change much but the sensor temps do. So if the monitor temps are not changing it could indicate that a sensor is not transmitting.

So bottom line, watch the changing temps.
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Old 12-08-2013, 09:15 AM   #10
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That's a very good point to keep in mind when choosing a TPMS.

My Tire SafeGuard TPMS does not operate that way.

It has an auto-drop-and-hook feature that if the car were to drive away the monitor recognizes that and it reports nothing for the car. And if the monitor were to be put into the car and again you drove the car somewhere, the monitor will not report anything for the coach.

Of course you can push some buttons and reprogram the screen to temporarily eliminate the vehicle that you have "dropped".

However, with everything attached and working, if it loses a signal for one sensor too long it will report that the signal has been lost or the sensor is gone.

Every TPMS is different so it's just a matter of finding one that works for you.

Dr4Film ----- Richard
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Old 12-08-2013, 09:21 AM   #11
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Quote:
Originally Posted by greystroke View Post
One thing that has not been mentioned that is very important.

The TST monitor only receives info and does not transmit. The sensors send info about every two minutes to the monitor unless there is a radical change, then it will transmit the problem such as leaking etc.

But and this is a big but, what if the sensor malfunctions and does not transmit any more???

What happens is the monitor will display the last known reading and hold it until it receives another transmission from the sensor. In other words the reading on the display will not change until until it receives updated info.

My monitor will not alarm if it has not received a transmission from a tire in longer than 2 minute time frame. It simply displays last known info.

The way I found this out was after disconnecting the toad one day, DW drove to the store miles away and the toad readings remained frozen on the display. When she returned the frozen readings started updating again. Try it when you disconnect.

So because of this problem I monitor temps more closely because when everything is stable on the road such as speed and outside air temp the pressures don't change much but the sensor temps do. So if the monitor temps are not changing it could indicate that a sensor is not transmitting.

So bottom line, watch the changing temps.
Our 507 system does not operate in this manner. A couple times we've disconnected the Jeep and been gone for some period of time. When we got back the monitor was beeping and flashing. It had realized the Jeep was out of range and was sending a warning.

Now we either shut it off when we leave with the Jeep or press the mode and _ buttons for 3 seconds so the system doesn't monitor the Jeep. The downside of eliminating the Jeep from the monitoring cycle is that you have to remember to activate it before hitting the road with the combination.
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Old 12-08-2013, 09:56 AM   #12
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Quote:
Originally Posted by Dr4Film View Post
That's a very good point to keep in mind when choosing a TPMS.

My Tire SafeGuard TPMS does not operate that way.

It has an auto-drop-and-hook feature that if the car were to drive away the monitor recognizes that and it reports nothing for the car. And if the monitor were to be put into the car and again you drove the car somewhere, the monitor will not report anything for the coach.

Of course you can push some buttons and reprogram the screen to temporarily eliminate the vehicle that you have "dropped".

However, with everything attached and working, if it loses a signal for one sensor too long it will report that the signal has been lost or the sensor is gone.

Every TPMS is different so it's just a matter of finding one that works for you.

Dr4Film ----- Richard
Good point. I wish I had an alarm for non-transmitting sensor. As it it only alarms like that on system startup. I have had one sensor do this to me but I caught it in time. So I watch my temps.
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Old 12-08-2013, 10:05 AM   #13
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Originally Posted by Hikerdogs View Post
Our 507 system does not operate in this manner. A couple times we've disconnected the Jeep and been gone for some period of time. When we got back the monitor was beeping and flashing. It had realized the Jeep was out of range and was sending a warning.

Now we either shut it off when we leave with the Jeep or press the mode and _ buttons for 3 seconds so the system doesn't monitor the Jeep. The downside of eliminating the Jeep from the monitoring cycle is that you have to remember to activate it before hitting the road with the combination.

Another good point. But my problem doesn't just concern the toad but any sensor that malfunctions and quits transmitting when it initially started up ok. I watch for this now by watching temps. I love this system but I can trust it to alarm if the sensor transmitter fails. It is what it is.
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Old 12-08-2013, 10:26 AM   #14
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My thoughts FWIW:

1. Yes...most any TPMS PSI reading is best used as a comparative tool.

2. Temp measurements are also best used as a comparative tool. Perhaps the only exception would be those with internal sensors.

The trick is to LEARN what is normal. After one installs a TPMS they should carefully set/monitor tire pressures and then make some mental notes on how they react under varying conditions. As an example I noted that my front right tire of my toad runs 6*-8* warmer than the rest. Any guess where my MH exhaust is? LOL So far that hasn't presented any temp alarms but if it did, I would probably tweak alarm parameters. I also have noted a 1-2 PSI difference in that tire compared to other toad tires but again, not enough to cause over pressure alarms and would be expected given the extra heat.

I tend to agree that the temps are closer to ambient than internal tire temps. I am a tad concerned that the minimum 158* F temp setting is too high given my observations. I would like to see either a lower minimum temp and/or a comparative temp based alarm.

All that being said, I don't think that any other TPMS has any particular advantage over TST and visa versa. I'm happy with TST costumer service and that is important.
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