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Old 09-25-2022, 10:17 AM   #1
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Tire Pressure Monitoring Systems – Peace of Mind or POS?

At the insistence of my co-pilot, we installed a (EEZ) TPMS for “peace of mind” on our next long road trip which we are on now. My experience has been a bit frustrating with it and I was looking for insight on your experiences. If you don’t want to read the entire preamble, please go directly to the numbered questions below. Thoughts on any of it would be appreciated. Thanks!!

We are running Micheline 275/80R22.5 XZE2 tires on a 2018 Tiffan 33AA. After weighing it, determined cold inflation should be 90psi front and 95psi rear based on Micheline chart (+10% for interior load). Towing a 2003 Ford Ranger, which got the TPMS installed too.

The configuration, programming and installation was very easy. The instructions say to set the high/low pressure alarms at 20% above and 10% below the tire pressure (cold I assume) which is where we set them initially. So, we set alarms to 108/81 psi for the front and 114/86 psi for rear. We left high temp alarm at default of 158F.

I found it difficult to get stable pressure readings. I am a (retired) mechanical engineer so probably get a bit obsessed about instrumentation readings and maybe I expect too much. I kept futzing with pressure trying to get them to read the same cold pressure prior to the trip. I would bleed air out and the reading on the TPMS would not change. More iterations. Next thing I know, it’s reading 3 psi lower. Anyway, finally dialed it in till they read within 1F of each other. I noted that the TPMS read 1-2 psi above the gauge I was using for the RV tires and right on for the (lower pressure) gauge I was using for the toad. This is to be expected given there is no assurance of standardization/calibration on my gauges.

On the first day we hit the high pressure alarm on the DS rear inner going to 116psi and PS front going to 108psi. So we raised the Alarm to 110 front and 116 rear. Also, the next morning I let a bit of air out of the DS rear wheels as they both read a little high so we could start out more even.

On the second day (with higher alarm points) we hit the high pressure alarm on PS front, PS rear both and DS rear inner (112, 116, 119, 118 psi respectively). Note, I normally drive at 63-65mph. On this day when reaching these pressures, we exceeded 70mph coasting on long straight runs out of the mountains which I know causes more heat. The ambient temperature was also about 10F higher than previous day.

The manual says to expect 1psi expansion per 10F of temperature rise. I recorded all the data and based on the TPMS pressure and temperature readings we were experiencing about 7psi per 10F on the RV and 2 psi per 10F on the toad. So I suspect the data they are giving is NOT for large motorhome tires.

Questions:
1. Are others experiencing pressure increases from cold exceeding 20% on their RV tires?
2. It seems to me that the huge pressure increase makes the low pressure alarm less useful. If the pressure goes up 20% and you are set 10% low from cold, that is a 30% drop that needs to occur before the low pressure alarm goes off. At a nominal 100psi inflation, that is a 30psi drop required. I think I will set the low pressure alarm at 1-2 psi below cold inflation pressure rather than 10% low as recommended. Thoughts?
3. The user manual says the sensors measure the air temperature in the tire. With long valve stems and no air flow through the sensor, how can that be? The sensor is whipping through the wind so it would seem the temperature would be more influenced by ambient temperature and wind speed. Except when you are stopped, just ambient. The rear inners read hotter as one would expect so there is at least some relative relationship. Usefulness of the temperature reading??
4. Does a TPMS really offer peace of mind for large tires or is it just another gadget to potentially annoy and fail?
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Old 09-25-2022, 10:30 AM   #2
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Tire Pressure Monitoring Systems – Peace of Mind or POS?

I also have the Eez tire system with 12 cap sensors for 3 years now. I think you are over thinking this.

Set the tire pressures with an accurate gauge before screwing on the sensors, then DON’T mess around with them. Yes, the sensors all have a variance, and will not read the same, but don’t worry about it unless they are off by 5psi or more from what you know you set them to.

Tires in the sun will heat up and show pressure increases higher than ones in the shade.

Your toad vehicle tire directly behind motorhome exhaust will show higher pressure and temperature than other 3 tires.

If your tires are heating up excessively, it may be because they are under inflated, and the sidewalls flexing is creating heat.

My 315/80 22.5 front tires are inflated to 120psi cold but will increase to 133 while driving. The drive and tax axle tires increase less per tire…. Maybe 7psi

I would not drive without my system. Any slow leak will report before the tire experiences a blow out.
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Old 09-25-2022, 11:23 AM   #3
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TPMS systems have prevented me from starting out with a very underinflated tire three times.

My current and previous system had a stated psi accuracy of +/- 3%. When inflated to 110psi with a known-good guage, that's a fairly large spread.

The point of a TPMS is not to act as a tire guage. It's purpose is to sound an alarm if pressure is way low or way high, and more importantly to alarm on rapid decrease in pressure or increase in temperature.
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Old 09-25-2022, 11:25 AM   #4
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Your way overthinking this. For a few hundred dollars you are NOT going to get the precision you are trying to achieve and that is not what these monitors are designed to do. We have had this system for 6 years and it has saved us a few times. Fill you tires using a good tire gauge and leave them alone. Note the readings on the display and use those readings as your baseline. Cold temps will increase on each tire based on amount of time driving, which side of the rig is in the sun and whether you are driving on concrete or asphalt surfaces. So if you use minimal numbers you will get lots of false alarms. These monitors will tell you of sudden loss in tire pressure and sudden overheat situations immediately instead of after the fact and while you are cruising down the road. That's it and it helps tremendously. It saved our bacon a couple of times and saved us big expense. I check air pressure with my gauge before each trip, for us that means removing sensors, and as long as the display shows each tire, I use whatever pressure that it shows and being OK unless it is really strange. Can't remember offhand what temp limits we use but the sensor on the toad saved us when the Brake Buddy breakaway switch pulled out on the highway and all of the brakes we locked. The temp Alarm saved us. It doesn't have to be at the lowest setting, just high enough to let you know there is a problem. Our temps increase anywhere from 10 to 25 degrees, depending on all the factors I mentioned. So I would never use 25 degrees over the cold temps as a limit. And cold temps can vary from day to day and which side of the RV is sitting in the sun. Are you going to adjust tire pressure every hour and which side faces the sun? Will you adjust limits based on your daily or hourly adjustment? Will you ever get out of your parking space? Unless we sit for a few weeks or more, we make no adjustments to anything and when we do, it's only to tire pressure IF NEEDED. We have an older version of the same unit you have. Chuck
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Old 09-25-2022, 12:30 PM   #5
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I have the same TPMS. I just use the ‘trend is your friend’ method where I found tires on the sunny side can be 2 degrees higher starting out. As you founn, the inner duals run warmer and the towed vehicle runs warmer due to exhaust location.

On my tire pressures I added what amounts to a 13% safety margin. (Michelin RV chart says 95, I run 110 etc.)

Drove into NC mountains from Florida temp in the morning went from 75 to mountains 55. I checked the TPMS once but all tires were trending low. I decided to monitor as they warmed up and they were all close.

Don’t know why your alarms were going off unless it is needing a safety margin inflation. I’d rather be a little high than a little low.

You can also contact EEZ, they are very responsive and may have some ideas.
Hope this helps
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Old 09-25-2022, 01:08 PM   #6
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1. Are others experiencing pressure increases from cold exceeding 20% on their RV tires? No
2. I think I will set the low pressure alarm at 1-2 psi below cold inflation pressure rather than 10% low as recommended. I follow the TT-600 recommendation.
3. Usefulness of the temperature reading?? High temp warning but the pressure is OK, then your sensor has detected high temp from metal components that transfer heat faster than rubber. This might indicate a bearing or brake problem which should be checked as soon as possible.
4. Does a TPMS really offer peace of mind for large tires or is it just another gadget to potentially annoy and fail? Yes.......cheap insurance. I monitor 10 tires each on my tow vehicle/trailer and motorhome/toad. They provide a good check pror to a trip.
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Old 09-25-2022, 06:14 PM   #7
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My canned thoughts on the settings of the TPMS system for a motorhome:

- Motorhome tires should have their MINIMUM pressures set by the actual "as weighed" weight from the tire manufacturer's manual, also called the inflation chart.

- If you have never had the motorhome weighed, start with the pressures on the inside sticker. Those pressures, by law, are the MINIMUM pressure needed to fully support the design weight rating of each axle, its GAWR (gross axle weight rating) when using the tires installed by the motorhome manufacturer.

- If you are using an axle weigh, such as a CAT Scale, the generally-accepted wisdom is to add 5% to the total axle weight before looking up the inflation chart. The load inflation charts assume an even weight distribution left-to-right and that's a good assumption for a car or a truck, but not an RV.

RV's can have as much as a 10% difference in weight between the driver side and the passenger side. If you use the load inflation charts with the real axle weights you can be under-inflating one tire, the heavier side. On ours that could be a 5 PSI under-inflation and if the weights were shifted a bit it could be a 10 PSI under-inflation on the heavier side tire.

- NEVER try to extrapolate the load inflation chart numbers. Always use the next higher weight in the chart if you're between two.

I actually add an extra 10% over the inflation chart to accommodate for day-to-day temperature variations without having to "chase" the tire pressures. I only have to add air maybe once a year on our Class A.

For example, before we leave Florida in early April I'll have the tires at about 100 PSI even though my sticker pressure is 90 PSI. When I get to northern Ohio a week later with temps in the mid-30's the tire pressures will be in the low 90's for all tires. I will not need to adjust the tire pressures until we leave in November, maybe not even then.

- The pressure molded into the sidewall of a tire is a constant source of confusion. It is NOT the maximum pressure the tire should ever see. It NEVER is.

That molded pressure is the MINIMUM air pressure needed in the tire to safely support the MAXIMUM weight that the tire is designed for when cold. That's it; nothing more.

NEVER let air out of a hot tire even if the pressure is higher than the molded sidewall pressure. The pressure will drop as the tire cools. DO NOT exceed the pressure on the sidewall when inflating the tire cold either.

- LOW PRESSURE ALARM - This is the critical alarm. A tire that is 20% below the required pressure is considered flat and subject to hidden damage.

The LOW PRESSURE alarm should be set to no lower than 10% below the required cold pressure to give you an adequate amount of time to get pulled over, add air to get to a tire shop, or whatever is needed.

For example, if your tires are supposed to be set cold to 90 PSI to handle the weight they're carrying, then the Low Pressure alarm should be set to alarm at no lower than 81 PSI and 72 PSI is considered flat.

So is "cold" a specific temperature or what? No. It simply means "Whatever today's temperature is before the tires are driven on and before the direct sun touches the tires."

- HIGH PRESSURE ALARM - As long as the cold pressure is set appropriately for the actual weight of the motorhome axles (or corners), the pressure increase while traveling is pretty much irrelevant.

Why? Because the tires are designed to easily handle those pressure increases as long as the tires are not overloaded. The pressure increases are normal and they are expected. Again, NEVER let air out of a hot tire. Never.

- HIGH TEMPERATURE ALARM - On a motorhome it's pretty much useless as long as the tires are not underinflated or overloaded. That's why the default is set so high, close to 160 degrees F. I leave mine set to the default. It's the temperature of the layers of tread that's important, not the temperature of the air in the valve stem.

That large metal wheel also acts as a heat sink. Unlike a trailer with smaller wheels and tires, the large wheels and tires can dissipate some heat from a bad wheel bearing or a dragging brake. That makes a TPMS "high temperature" alarm less useful on a motorhome for detecting mechanical failures.

- A TPMS, while driving, should be considered more of a trend monitor.

In other words, if all of the tires are behaving essentially the same and all of the tires are behaving essentially as you know they have in the past, the absolute numbers are not that important.

- Separate TPMS display or a phone app for the display? Do you really want a critical safety feature dependent on a phone being charged or on some phone update breaking the TPMS functionality? Not me but perhaps you are OK with that.

Make sense?

Ray
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Old 09-25-2022, 06:39 PM   #8
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Quote:
Originally Posted by johnhicks View Post
TPMS systems have prevented me from starting out with a very underinflated tire three times.

My current and previous system had a stated psi accuracy of +/- 3%. When inflated to 110psi with a known-good guage, that's a fairly large spread.

The point of a TPMS is not to act as a tire guage. It's purpose is to sound an alarm if pressure is way low or way high, and more importantly to alarm on rapid decrease in pressure or increase in temperature.
X2 on the above......If you keep messing with adjustments, you'll go crazy. Over about a years' time, I had to change my temp alarms twice to get to where it didn't unnecessarily alarm in hot weather. Mine also set off the alarm on the toad right front tire while hill climbing into Vegas. That was caused by the exhaust on the RV.
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Old 09-25-2022, 07:49 PM   #9
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My tire psi are set at 80/85.
Not uncommon to see more than 100psi during the drive.
I checked /adjusted tire psi 3 weeks ago before leaving on a trip to Yellowstone while at home with temps in 80's. Using the EEZ recommendation of setting the high pressure, I was getting the alarm so often, I just raised the high limit way up to basically 'disable' the high press alarm.
While in YS and leaving in the morning with temps in the 40's, my tire psi's were as low as 65. After a short drive, tire psi's were back up to reading normal as before.
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Old 09-25-2022, 09:28 PM   #10
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Thanks. Issue was not with high temperature. Just trying to understand what to expect with high pressures.

Agreed. Just set it and don't mess with it. I will just run the high pressure alarm points up.

Your point about the exhaust affecting the toad tire is a good one. I did notice it running hotter. Thanks.
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Old 09-25-2022, 09:31 PM   #11
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Thanks. I will be sharing your attitude as trend friend. I was mostly surprised at how much pressure they gained from cold.
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Old 09-25-2022, 09:32 PM   #12
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Thanks. Have already considered the canned thoughts. In preamble to questions I laid out my approach of weighing etc. Thanks for feedback.
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Old 09-25-2022, 09:33 PM   #13
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Well, I went crazy years ago so the TPMS won't drive me any further!

Your point about the exhaust affecting the toad tire is a good one. I did notice it running hotter. Thanks.
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Old 09-25-2022, 09:36 PM   #14
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Thank you. This was the response I was looking for. You are getting a very healthy pressure rise and have raised the high limit to accomodate. This is what I have done as well. My one "concern" again is that the low pressure alarm will take a while to hit the low state when tire pressure goes so high. But as others have implied: look at it from the macro point of view, not the micro. And watch the trends.
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