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Old 03-02-2024, 11:05 PM   #1
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THOR #23246
Tire Pressure Variation

I recently took my RV out for an exercise drive and noted that the TPMS on one of the tires was reading higher than the others, though they were all within a degree when cold. The difference was about 5-6 psi (101 vs 96 on the corresponding position on the other side of the axle) and it was on the driver side, inside dually position. PSI was measured by TPMS system in motion.

Pressure being a function of temperature, that tire is warmer than the rest. I am wondering why that might be. The exhaust pipe makes a bend in front of the dualies on that side, so that might explain it, but only the inside is higher.

Anyway, I would appreciate the forum's experience and thoughts on whether this psi increase is significant or not and if the exhaust bend there would explain it.

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Old 03-02-2024, 11:15 PM   #2
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First did you compare the TPMS readings to a stick guage?

What TPMS system, some are good and others are crap.

If your TPMS is not throwing an over pressure or over temp alarm donít worry. The tires will not raise temp or pressure at the same rates.
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Old 03-02-2024, 11:37 PM   #3
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Quote:
Originally Posted by CactusJuice View Post
I recently took my RV out for an exercise drive and noted that the TPMS on one of the tires was reading higher than the others, though they were all within a degree when cold. The difference was about 5-6 psi (101 vs 96 on the corresponding position on the other side of the axle) and it was on the driver side, inside dually position. PSI was measured by TPMS system in motion.

Pressure being a function of temperature, that tire is warmer than the rest. I am wondering why that might be. The exhaust pipe makes a bend in front of the dualies on that side, so that might explain it, but only the inside is higher.

Anyway, I would appreciate the forum's experience and thoughts on whether this psi increase is significant or not and if the exhaust bend there would explain it.
You gotta take aftermarket end-of-valve stem TPMS senor temperature readings with a grain of salt. Think about where the temperature is monitored vs the bulk of tire air. They're more likely to measure ambient and direct sun temperatures than the temperature in the tire itself.
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Old 03-02-2024, 11:54 PM   #4
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Originally Posted by CactusJuice View Post
I recently took my RV out for an exercise drive and noted that the TPMS on one of the tires was reading higher than the others, though they were all within a degree when cold. The difference was about 5-6 psi (101 vs 96 on the corresponding position on the other side of the axle) and it was on the driver side, inside dually position. PSI was measured by TPMS system in motion.

Pressure being a function of temperature, that tire is warmer than the rest. I am wondering why that might be. The exhaust pipe makes a bend in front of the dualies on that side, so that might explain it, but only the inside is higher.

Anyway, I would appreciate the forum's experience and thoughts on whether this psi increase is significant or not and if the exhaust bend there would explain it.
Even though I set the tires to the same pressure by gage and the TPMS on all 6 tires as I drive the tires will read different pressures because they heat up differently. This is because:
  1. The tires do not have the same load no matter how carefully to try to balance the load. On my coach the Right front carries about 300# more weight than the Left front. Because of this the right tends to show a higher pressure
  2. Because of the lower air flow around the inside dually those tires tend to show a higher pressure.
  3. Tires that are exposed to sunlight will tend to show a higher pressure. So, if you are driving west the Left side tires, left front and outside rear tires will tend to show a higher pressure. this is the reason you should check pressure first thing in the morning before the sun warms the tires.
  4. Finally, the heat from the radiator and exhaust system will affect the tire pressures causing the inside rear tires to gain more pressure. On my coach the exhaust runs on the right side of the frame but crosses over the frame just ahead of the rear axle and exits just in front of the left rear tire. This will heat the Right inside tire to heat more and the left outside tire to heat more.

Having the pressure increase at different rates on each of the tires is normal. On my coach the tires can increase pressure by as much as 25psi as I drive. This is normal, the tire manufacturers take this into account in the tire design.

The temperature readings from Valve stem mounts TPMS sensors is useless IMHO. This is simply because the sensors are floating out in the airflow and not directly in contact with the tire or wheel. I once observed a 150 degree reading from one of my sensors while the coach was parked for at least two days. I think this was caused by sunlight reflected from the stainless wheel liners in much the same way a magnifying glass focuses the light to a single point.
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Old 03-03-2024, 12:38 AM   #5
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Here is an example of pressure and temperature variations. I set these to 84 PSI at a 30-degree air temperature. Outside temperature is now about 75 here in Mesa AZ where I am camped. Although the tires are now in shade the right-side tires receive much more sunlight.
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Old 03-03-2024, 10:30 AM   #6
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Quote:
Originally Posted by CactusJuice View Post
I recently took my RV out for an exercise drive and noted that the TPMS on one of the tires was reading higher than the others, though they were all within a degree when cold. The difference was about 5-6 psi (101 vs 96 on the corresponding position on the other side of the axle) and it was on the driver side, inside dually position. PSI was measured by TPMS system in motion.

Pressure being a function of temperature, that tire is warmer than the rest. I am wondering why that might be. The exhaust pipe makes a bend in front of the dualies on that side, so that might explain it, but only the inside is higher.

Anyway, I would appreciate the forum's experience and thoughts on whether this psi increase is significant or not and if the exhaust bend there would explain it.
It is very common for tire pressures to vary. If you have a decent TPMS you should be able to see that the tires on the side of the RV where the sun is will have a slightly higher pressure than those on the other side. The cold tire pressure when you start the driving day will increase, especially in the summer. It is my opinion that folks get wrapped around the axle when it comes to tire pressure. When you decide on the tire pressure best for your application you should fill the tires to those pressure when the tires are cold and don't get concerned when they change during the driving day. One does need to check cold tire pressure about once a month to adjust for seasonal changes.

The main purpose for the TPMS is to warn you when a tire fails or has extremely low pressure. Driving on an extremely under pressured tire is a recipe for disaster.
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Old 03-03-2024, 03:27 PM   #7
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Originally Posted by Dan-sr@perra-us.net View Post
Here is an example of pressure and temperature variations. I set these to 84 PSI at a 30-degree air temperature. Outside temperature is now about 75 here in Mesa AZ where I am camped. Although the tires are now in shade the right-side tires receive much more sunlight.
I have the same TPMS. I get it about the sun, shade, inside, outside etc, but mine read going 70 mph down the road for the rear axle - (they all started same (+/- 1) before hitting the road).

94, 101,96,94.

If you saw that on the bottom row of the TPMS, would you just dismiss it as variance within tolerance due to benign factors or worry that there might be a problem with the high tire?
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Old 03-03-2024, 04:21 PM   #8
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I have the same TPMS. I get it about the sun, shade, inside, outside etc, but mine read going 70 mph down the road for the rear axle - (they all started same (+/- 1) before hitting the road).

94, 101,96,94.

If you saw that on the bottom row of the TPMS, would you just dismiss it as variance within tolerance due to benign factors or worry that there might be a problem with the high tire?
That falls in the normal range of variations. I would guess you may also have had a slight crosswind coming from the right side. I normally see the right inside rear tire with the highest pressure with all the tires starting at the same pressure. A lot depends on the chassis. For example, my F53 chassis has the cat and muffler located on the right side of the right frame rail with the tail pipe exiting on the left just in front of the rear tires. If you have an F53 chassis motorhome that is probably how yours is configured as well.
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Old 03-03-2024, 06:07 PM   #9
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Ok so far, the gist of what I get out of this thread is.
1: The tire temperature feature of the TPMS sensors is basically worthless
2: There are a lot of garbage TPMS systems out there
3: It is a known fact tire pressure will increase substantially over the course of a driving day
4: Tire pressure increase is variable based on corner weights and relative to sunlight exposure
5: The main reason for TPMS is to tell you a tire **failed while driving

** That IMHO is the most important benefit of TPMS to let the driver know what is going on with the toad's tires and inner dualies.
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Old 03-03-2024, 07:01 PM   #10
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Quote:
Originally Posted by CactusJuice View Post
I recently took my RV out for an exercise drive and noted that the TPMS on one of the tires was reading higher than the others, though they were all within a degree when cold. The difference was about 5-6 psi (101 vs 96 on the corresponding position on the other side of the axle) and it was on the driver side, inside dually position. PSI was measured by TPMS system in motion.

Pressure being a function of temperature, that tire is warmer than the rest. I am wondering why that might be. The exhaust pipe makes a bend in front of the dualies on that side, so that might explain it, but only the inside is higher.

Anyway, I would appreciate the forum's experience and thoughts on whether this psi increase is significant or not and if the exhaust bend there would explain it.
What model and year coach do you have. If you post that information perhaps someone with the same coach can lend their experience.
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Old 03-03-2024, 07:21 PM   #11
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Originally Posted by MJC62 View Post
Ok so far, the gist of what I get out of this thread is.
1: The tire temperature feature of the TPMS sensors is basically worthless
2: There are a lot of garbage TPMS systems out there
3: It is a known fact tire pressure will increase substantially over the course of a driving day
4: Tire pressure increase is variable based on corner weights and relative to sunlight exposure
5: The main reason for TPMS is to tell you a tire **failed while driving

** That IMHO is the most important benefit of TPMS to let the driver know what is going on with the toad's tires and inner dualies.
When the failure occurs on the coach, we would all know it without the benefit of a TPMS system. We have all herd the stories of a toad having a flat with the motorhome driver clueless about the problem. Actually, the main reason to have a TPMS is warn that a tire is losing air before it goes entirely flat so that an issue can be addressed before a catastrophic failure occurs. The point is to prevent a sudden tire failure occurring while driving 70 mph caused by improper low inflation.
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Old 03-03-2024, 08:59 PM   #12
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When the failure occurs on the coach, we would all know it without the benefit of a TPMS system. We have all herd the stories of a toad having a flat with the motorhome driver clueless about the problem. Actually, the main reason to have a TPMS is warn that a tire is losing air before it goes entirely flat so that an issue can be addressed before a catastrophic failure occurs. The point is to prevent a sudden tire failure occurring while driving 70 mph caused by improper low inflation.
There are different types of failures, not all are catastrphic blowouts.

A couple years ago we stayed at my Wife's Aunt's house for a couple of days. When we got ready to leave I noticed the RH inside dually was at 61 PSIinstead of the normal 82 PSI. Pumped it up before we left but noticed it getting low less than an hour down the road. Stopped and pumped it back up again. We were on a short leg that day to another friends house. When we got there I "leveled" that side off the ground and spun the tire to examine it. I found a finishing nail in the shoulder leaking slowly. The next day we nursed it home and was able to do this because of the TPMS.
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Old 03-04-2024, 01:29 AM   #13
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Are all tires the same model & size? Even tires of the same size but from different manufacturers will have slightly different rolling radius, construction, etc which would likely explain differences in pressure & temperature in use.

I was thankful for our TireMinder TPMS when we were towing a car trailer on I-95 in Connecticut. The TireMinder alerted me to a falling tire pressure in a trailer tire. I was then able to exit the highway & find a good spot to stop, inspect the tire and swap to the spare. (it was a leaking valve stem)
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Old 03-04-2024, 01:34 PM   #14
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Are all tires the same model & size? Even tires of the same size but from different manufacturers will have slightly different rolling radius, construction, etc which would likely explain differences in pressure & temperature in use.

I was thankful for our TireMinder TPMS when we were towing a car trailer on I-95 in Connecticut. The TireMinder alerted me to a falling tire pressure in a trailer tire. I was then able to exit the highway & find a good spot to stop, inspect the tire and swap to the spare. (it was a leaking valve stem)
All the same with respect to brand, size etc. But that is an area of concern for a different reason and maybe what is eating at me.

I had my RV aligned a while back when I noticed uneven wear on the front tires. Toe was way off spec causing the outer edge to wear. It was readily visible on one of the tires upon inspection. The tire was not worn down to the cords or anything not even to the wear bars, but the siping was gone on the outer tread "bands" to some extent relative to the others.

The shop rotated the tires and the one with the most uneven wear ended up on the very position that I am now concerned about with respect to heat/pressure. That might explain it. I have driven around with uneven wear on my cars at times for years and never had a problem. But then, I never had a TPMS before either.
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Old 03-04-2024, 03:18 PM   #15
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All the same with respect to brand, size etc. But that is an area of concern for a different reason and maybe what is eating at me.

I had my RV aligned a while back when I noticed uneven wear on the front tires. Toe was way off spec causing the outer edge to wear. It was readily visible on one of the tires upon inspection. The tire was not worn down to the cords or anything not even to the wear bars, but the siping was gone on the outer tread "bands" to some extent relative to the others.

The shop rotated the tires and the one with the most uneven wear ended up on the very position that I am now concerned about with respect to heat/pressure. That might explain it. I have driven around with uneven wear on my cars at times for years and never had a problem. But then, I never had a TPMS before either.
Now you are getting into questions that will receive better answers if you provide the following information.
  1. What model RV?
  2. What Year RV?
  3. What is the dot date on your tires? How old are the tires?

Certainly, if the tires are nearing 10-years old you should consider replacement.
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Old 03-09-2024, 08:27 PM   #16
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I had 6 new tires installed my 2016 Thor Gemini and I do have a what I feel an expensive TPMS system and the RR inner dually tire pressure always rises 8to8 degrees higher than the others but the tire temperature stays the same as the outer. I even changed the sensors around but this tire reads as it previously did. So it is not the sensor. I even moved it to a different location on the monitor, but no different. Ummm. I believe itís in the tires. All tires are not the same even though same Brad and all new. Thatís just the one out of six that raises at a higher rate.
I agree now the the TPMS. Systems are mainly for a quick tire release while driving.
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Old 03-10-2024, 02:25 AM   #17
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I had 6 new tires installed my 2016 Thor Gemini and I do have a what I feel an expensive TPMS system and the RR inner dually tire pressure always rises 8to8 degrees higher than the others but the tire temperature stays the same as the outer. I even changed the sensors around but this tire reads as it previously did. So it is not the sensor. I even moved it to a different location on the monitor, but no different. Ummm. I believe itís in the tires. All tires are not the same even though same Brad and all new. Thatís just the one out of six that raises at a higher rate.
I agree now the the TPMS. Systems are mainly for a quick tire release while driving.
Since the temperature sensor(s) on the rear tires are likely connected to some sort of extension, you are measuring the temperature of the air going past the outside tire. Unless the TPMS sensor is in contact with the tire in some manor it cannot measure the tire temperature. I just ignore any temperature readings because of this. The inner rear tires will gain more pressure because they are exposed to the exhaust system heat and the Radiator heat flowing under the RV. On my F53 chassis the muffler and cat are on the right side of the right frame rail. Because of this the right side inside rear tire alwayes runs a higher presure.
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Old 03-10-2024, 03:53 AM   #18
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Since the temperature sensor(s) on the rear tires are likely connected to some sort of extension, you are measuring the temperature of the air going past the outside tire. Unless the TPMS sensor is in contact with the tire in some manor it cannot measure the tire temperature. I just ignore any temperature readings because of this. The inner rear tires will gain more pressure because they are exposed to the exhaust system heat and the Radiator heat flowing under the RV. On my F53 chassis the muffler and cat are on the right side of the right frame rail. Because of this the right side inside rear tire alwayes runs a higher presure.
As I mentioned in post #3 of this thread. But hey: why read the entire thread?
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