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Al F

TPMS Limitations? Opinions??

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While I am driving I periodically cycle through my TPMS monitor and view the pressure in all my tires.

I look for 2 things.  First that none of the tires are somewhat lower than what I expect their pressure to be.  The other is that the pressure is not somewhat higher than what I expect it to be.

The reasoning behind this is:

The following numbers are not intended to be exact, but used for operational representation.  If your TPMS triggers at 12% or 15% loss in pressure, then use those figures. 

--  If I start out the day with the air temperature at 65-70 degrees and my tire pressure at 90 psi,(and my TPMS sensor is set to the 90psi level) in the afternoon with the air temp now at 90 degrees or higher, the pressure will be in the range of 105 psi.  To me this means my proper operating pressure is 105psi.  If I now have a leak and loose 10% of the pressure my tire pressure will be 94.5psi.  This pressure drop will not trigger the TPMS (my assumption) since my TPMS is set to trigger the alarm at a 10% drop from the 90psi starting point. That is it won't trigger until the pressure drops to 81psi.  If I wait until the 81psi point, my tires will have been running at up to about 23% below the proper operating pressure.  The 23% below proper pressure is a very significant reduction in tire pressure. 

Any thoughts or opinions about the above statement??

--  The other thing I look for is an unexpected increase in the pressure in a tire.  I believe if I see an unaccounted for increase in pressure, then there may be something wrong with the tire, such as a slipped belt or dragging brake causing the tire temperature and pressure to increase. 

 

I am aware that the inside tire on a dually will have higher temperature and therefore a little higher pressure than the outside tire.  Also tires on the sunny side will have a slightly higher pressure/temperature.

 

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My TST 507 TPMS allows me to set the pressure and temp trigger points wherever I want them. I typically set the pressures at 10% low and 15% high with the temps left at the default 158 deg. F.

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This amateur TPMS user does not agree with your statement. If your low pressure alarm is set at 81psi cold, a warm tire does not change that. You have determined 90psi is your minimum air pressure for your actual tire load, it doesn't matter if the tire is cold or hot. FWIW, a tire 20% lower than the minimum for your actual tire load is considered "run flat", and should be removed and inspected by a professional prior to re-use.

Forget about the pressure rise while driving unless your high alarm triggers, just like you did before a TPMS was invented.

 

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You are applying dynamic temperature changes to static load pressure settings.

The load rating you set your pressure for are for a "cold", meaning not moved more than a mile, tire.  It has nothing to do with the ambient temperature. The changes in pressure from moving and ambient temperature changes are built into the tire ratings.

Thus at 81 psi, you are withing the load pressure rating of the tire.

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8 hours ago, Ray,IN said:

This amateur TPMS user does not agree with your statement. If your low pressure alarm is set at 81psi cold, a warm tire does not change that. You have determined 90psi is your minimum air pressure for your actual tire load, it doesn't matter if the tire is cold or hot. FWIW, a tire 20% lower than the minimum for your actual tire load is considered "run flat", and should be removed and inspected by a professional prior to re-use.

Forget about the pressure rise while driving unless your high alarm triggers, just like you did before a TPMS was invented.

 

 

1 hour ago, Mark and Dale Bruss said:

You are applying dynamic temperature changes to static load pressure settings.

The load rating you set your pressure for are for a "cold", meaning not moved more than a mile, tire.  It has nothing to do with the ambient temperature. The changes in pressure from moving and ambient temperature changes are built into the tire ratings.

Thus at 81 psi, you are withing the load pressure rating of the tire.

I think both of you are missing my point. 

The point being, the TPMS alert/alarm will not trigger until the tire pressure reaches 81psi (cold pressure being 90psi).  However since my premise is that I am driving at 60mph in 90-95 degree or higher air temperature and the pressure in the tire has risen to 105psi due to the heat of the road, the flexing of the tire and the outside air temperature, IF I was to wait until the TPMS alarmed at 81psi that tire would be seriously under inflated.  Additionally the tire that alarmed at 81psi, if it was allowed to cool to the "cold" temperature, its pressure would probably be in the mid to upper 60's psi instead of the 90psi it should be.   On the other hand if I was to periodically visually monitor the pressure in all my tires and see that one tire is at 97psi while all the others are in the 105psi range, I would have an early detection of a problem, probably a slow leak, in that tire.

There is no dispute or question that the "cold" tire pressure should be set based on the tire load tables and the actual weight the RV is placing on the tire, as determined by a 4 corner weighting of the RV.  Nor is there any question that the increase in tire pressure due to flexing of the tire, heat from the asphalt, and the outside air temperature is built into the design of the tire. 

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My TST TPMS monitor scrolls through the tire locations constantly showing pressure and temperature. Each location shows for several seconds and then the display switches to the next location. If a tire's readings change rapidly, that location is displayed immediately. I have the monitor located on a flat spot in the dash right under the speedometer so that it is easy to see and check on a frequent basis. If I notice a change in pressure or temperature from what I expect or one tire reading is significantly different from the others, I get off the road and check things out. If a tire's pressure drops by more than a couple of psi while running at highway speed, I will stop as soon as possible to check things out. I have discovered two leaks from nails/screws in a tire before the tire lost too much air and was damaged needing to be replaced using this system. 

Edited by trailertraveler

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I don't inflate my tires to the minimum required for the required weight rating. With my tires inflated about 10% above the minimum or about 90 PSI for my coach, my 10% low TPMS trigger point means the tires are still within weight specs when the alarm sounds due to a pressure loss.

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What Dutch said.  If you follow his example you are fine setting the low press alarm like you do 10% below your cold set press. 

It’s a good idea to set pressures one or possibly two chart ratings above min rating   This will also allow for dynamic loading changes or actual load changes in nominal amounts  

Don’t suggest to go over max rated sidewall marked pressure for cold set press  

Set the high alarm 15% or more above set press. You may have to tinker a bit with these settings to stop nuisance alarms on very cold mornings and very hot driving days. 

 

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If what you are doing  works for you then keep it up..We have our TPMS 507  set at factory levels for years. we set the  our Rv tires psi at 110psi. the mps rotated through all the tires displaying psi and temp. There are many variables speed, out side temp, temp of the roadway, which side of the Rv is exposed t o the sun.We do watch for a drop before anything alarms . We have never changed the TPMS settings and never will. The only thing any TPMS will not do is alert to a blowout that is a sudden and catastrophic failure .

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The pressure pro and TST do alert immediately to sudden loss of total pressure. 

I can attest to that with a blowout bang and alarm same time.  They are designed for that. 

They do check the pressure and transmit revised readings about every two minutes. Enough time for a slower leak to notify. 

TST does have to be set up for alarm settings there are no factory settings as all press are going to be different for different users. . Only setting that is set up is high temp that is ok to leave along. 

So you have to set them on install. 

When I install these for folks I set them up for them. 

They are a great tool to have on our rigs.  Wouldn’t be without one. 

Edited by billr

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We prefer the PressurePro System where the lower and upper limits are set automatically when the sensor pressure is set by screwing the sensor on.  No programming other than to say I am putting a sensor on this wheel and putting the sensor on the wheel.

We also prefer the LED display which should all the wheel at once for alerts with a digital readout for the exact error.  Big deal when the toad wheel took a hit from road shrapnel and we got to the side of the road with 10 psi still in the tire.  The alarm went off and we immediately knew which wheel by its LED indicator.

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2 hours ago, billr said:

The pressure pro and TST do alert immediately to sudden loss of total pressure. 

Yes it  does but it has already happened... bang ..alarm..it can not alert you that you are going to have a blowout a blow out is a sudden and catastrophic failure .

2 hours ago, billr said:

I can attest to that with a blowout bang and alarm same time.  They are designed for that. 

They do check the pressure and transmit revised readings about every two minutes. Enough time for a slower leak to notify. 

TST does have to be set up for alarm settings there are no factory settings as all press are going to be different for different users. . Only setting that is set up is high temp that is ok to leave along. 

So you have to set them on install. 

When I install these for folks I set them up for them. 

They are a great tool to have on our rigs.  Wouldn’t be without one. 

 

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5 hours ago, Mark and Dale Bruss said:

Not missing what you are saying.  But you are on the wrong path of thinking and you ignore those who say you are.

Why?  Are you saying a tire with normal cold PSI of 90 is ok to run at 60mph on a hot sunny day with air temp at 95 degrees with the pressure at 85psi which is 4psi above what will cause the TPMS to alarm?  Note the air pressure is at 85psi because of a slow leak.

What am I ignoring? 

I am missing something here. 

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As the OP for this topic I totally agree with several of the statements/recommendations already given. 

--  If you can inflate your tires at 10% or 10psi over the cold psi for the weight you have determined is on the tire w/o exceeding the max pressure found on the sidewall of the tire, that is excellent.  And it is what I do.  That is also why, when I bought my current Class A, I upgraded to load range H instead of the load range G tires  that were on the RV when I bought. (also G tires are noted on the plack inside the RV) It needed new tires, the tires on the rig were original from 2006 and I bought the rig in 2014.

-- If you have a programmable TPMS then adjusting the alarm as suggested is a good idea.  I have Pressure Pro which cannot be programmed.  They are like what Mark and Dale said, screw them on and the high/low pressure is set based on the pressure the tire is at when you screw the sensor on the valve stem.

 

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OK, since you are all talking about TPMS (not PMS, right?)- I have a 5 yr old PP system, and now it needs a few sensors. It works, has several little idiosyncrasies I've learned to live with. But at 5 yrs old, is there anything better out there now? I have 14 sensors, and at $40-50 a pop it could get to the break point of a new system very suddenly. What's everybody using now?

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29 minutes ago, ARGO said:

OK, since you are all talking about TPMS (not PMS, right?)- I have a 5 yr old PP system, and now it needs a few sensors. It works, has several little idiosyncrasies I've learned to live with. But at 5 yrs old, is there anything better out there now? I have 14 sensors, and at $40-50 a pop it could get to the break point of a new system very suddenly. What's everybody using now?

I've been hearing good things about TST.  It has been mentioned earlier in this topic.  My PP is about 10 years old and a couple or 3 of the sensors are original.  Thinking of replacing the system as well.

I do suggest you start a new topic with your question though.  You will get a lot more responses from a new topic rather than adding on to an existing topic with a new issue or question.

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3 hours ago, richfaa said:

Yes it  does but it has already happened... bang ..alarm..it can not alert you that you are going to have a blowout a blow out is a sudden and catastrophic failure .

 

Yup I agree. It would not. 

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4 hours ago, richfaa said:

Yes it  does but it has already happened... bang ..alarm..it can not alert you that you are going to have a blowout a blow out is a sudden and catastrophic failure .

 

Since most blowouts are the result of overheating due to under inflation, a TPMS can be a valuable tool in avoiding catastrophic  tire failures. It can't, of course, alert you to that chunk of sharp steel scrap laying in the roadway just ahead though.

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Just my opinion but what most folks call a blowout was really a slow loss of PSI undetected if one does not have a TPMS .Once the psi dr opes to level that the tire comes off the rim the results can be the same as  blowout lots of noise, Rv damage , etc.I have seen it happen right in front of us .  We have been using TPMS for 11 years and it has saved us damage more than once.

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6 hours ago, Al F said:

Why?  Are you saying a tire with normal cold PSI of 90 is ok to run at 60mph on a hot sunny day with air temp at 95 degrees with the pressure at 85psi which is 4psi above what will cause the TPMS to alarm?  Note the air pressure is at 85psi because of a slow leak.

What am I ignoring? 

I am missing something here. 

Tire settings are determined from the "cold" (unmoved) position.   That is where the 10% under limit is determined. 

If the ambient temperature rises, or the flex action of the tire raises the tire air temperature, that does not change the base pressure for the tire load.  If anything, you will have a higher pressure so you are farther from the base low limit.

The tire load ratings are designed with the understanding that the temperature and pressure of the tire air will increase as the tire is used.

With your thinking, you could stop every half mile and adjust the tire pressure and kept the pressure within range.  But that is the absolute worst thing to do because you will be reducing the volume of air inside the tire and you will be under inflated when the temperatures recede.

The typical 25% upper limit usually covers any pressure increases from ambient temperature and tire usage.

 

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For the past 8 months we've been guinea pigs for the Tire Patrol system by RViBrake. We have put the system through rough roads, high and low temps and altitudes over 10,000 feet. We've hit the sensors with lateral and centrifugal stresses and I would be less  than honest if I didn't mention we're on probably our fourth full set of 10 sensors having discovered several different issues.  This new TPMS system uses a consolidated or unifying control center in conjunction with an android tablet to display the status of paired sub-systems. Our other tests involved the control center hub with placement, receiving sensitivity and yep, we found some issues with that as well and are on our third unit. The only part of the system we haven't had replaced is the android tablet though again, I would be less than honest if I didn't mention it could use a faster CPU and perhaps more memory (techno geek here).

Bottom line? I'm now pretty confident the system offers the versatility, reliability and ruggedness I can be happy with.  Now, to answer the OP question and the reason I had to explain this so much. This system displays all 10 sensors on one screen with the default as PSI and quickly selectable between it,  temp, or sensor signal strength. On the morning of our travel day my routine is to start the engine to air up and when I do, I turn on the system and check the display. The pressures shown are my cold temp pressures and I take the lowest displayed and use it as my trigger point for  low pressure. My high PSI trigger is usually set for 20lbs higher than the manufacturer's weight/operating pressure and I've kept the high temp trigger at 135 for front and rear axles on the motorhome (everything is obviously different for the toad).

I won't fully endorse the system yet as we've only got about 1000 miles without a hitch but I've been assured by the  designer and owner of RViBrake, Dan Decker, that we've pretty much chased the gremlins away. I will say I really like the concept of a consolidated system that will not only do the TPMS but the braking system and leveling of the rig - just for starters. Its a good system so far.

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10 hours ago, Mark and Dale Bruss said:

Tire settings are determined from the "cold" (unmoved) position.   That is where the 10% under limit is determined. 

If the ambient temperature rises, or the flex action of the tire raises the tire air temperature, that does not change the base pressure for the tire load.  If anything, you will have a higher pressure so you are farther from the base low limit.

The tire load ratings are designed with the understanding that the temperature and pressure of the tire air will increase as the tire is used.

With your thinking, you could stop every half mile and adjust the tire pressure and kept the pressure within range.  But that is the absolute worst thing to do because you will be reducing the volume of air inside the tire and you will be under inflated when the temperatures recede.

The typical 25% upper limit usually covers any pressure increases from ambient temperature and tire usage.

 

Other than your statement seeming to say I am advocating anything at all about changing air pressure as we drive, we are in agreement.  I just don't see anything in my wording about adding or reducing air pressure because the pressure increases as we drive.

My reason for starting this topic is to discuss the possibility that some TPMS systems could alarm way to late for low pressure in a tire.

For example:  assume both steer tires have proper cold inflation of 90psi for the weight of the RV.  Now while driving on a hot day that pressure increases to 105psi (which is normal for the conditions).  However if one of the steer tires develops a slow leak the TPMS won't alarm until the pressure drops to 81psi (10% below the 90psi cold pressure).  That 81psi, given the driving conditions, as far as everything I have ever read about proper pressures, is way, way to low and the tire is likely to be rendered unsafe to drive on, even it it looks OK on the outside of the tire. 

Please reply with the reasons you may believe my above example is incorrect.

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For the third time, you are assuming that the volume of air in the tire is not adequate as the ambient and operating temperature increases.  The volume of air necessary to support the tire load that is set when "cold" is what is needed through the operating temperature range of the tire.

A tire is not a balloon.  It is a fixed sized container.  The low level of internal air pressure is what keeps the tire from collapsing, overflexing the cord bodies.  That does not change because the outside temperature nor the internal temperature increases.  The pressure reading increases with heat but the volume of air remains the same.

The standard of using "cold" psi settings is a lot easier than determining if you have enough air mass with varying density air as the temperature changes.  Psi is an easier metric to follow but it is not an exact representation of what is happening inside the tire.

It isn't some TPMS systems, all TPMS systems have fixed lower limits.  Some let you program the lower limit, some do it for you but they all start with a fixed lower limit.  TPMS is not new, I have had a system for almost 12 years now. 

If this logic was invalid, someone would have come out with a different technology by now.  All the technology changes in the TPMS world have centered around being cheaper and adding questionable added readings like internal air temperature.  Questionable because the sensor is not inside but out in the air stream and increasing air pressure is the same as increasing temperature.  But gadgets sell.

You are just overthinking this.

 

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24 minutes ago, Mark and Dale Bruss said:

For the third time, you are assuming that the volume of air in the tire is not adequate as the ambient and operating temperature increases.  The volume of air necessary to support the tire load that is set when "cold" is what is needed through the operating temperature range of the tire.

A tire is not a balloon.  It is a fixed sized container.  The low level of internal air pressure is what keeps the tire from collapsing, overflexing the cord bodies.  That does not change because the outside temperature nor the internal temperature increases.  The pressure reading increases with heat but the volume of air remains the same.

The standard of using "cold" psi settings is a lot easier than determining if you have enough air mass with varying density air as the temperature changes.  Psi is an easier metric to follow but it is not an exact representation of what is happening inside the tire.

It isn't some TPMS systems, all TPMS systems have fixed lower limits.  Some let you program the lower limit, some do it for you but they all start with a fixed lower limit.  TPMS is not new, I have had a system for almost 12 years now. 

If this logic was invalid, someone would have come out with a different technology by now.  All the technology changes in the TPMS world have centered around being cheaper and adding questionable added readings like internal air temperature.  Questionable because the sensor is not inside but out in the air stream and increasing air pressure is the same as increasing temperature.  But gadgets sell.

You are just overthinking this.

 

You didn't respond to my example.  That's OK.  Other than your first sentence ("For the third time, you are assuming that the volume of air in the tire is not adequate as the ambient and operating temperature increases")  I am in agreement with what you just wrote and have been aware of that for a number of years.

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