TPMS alerted to a broken brake system.

 Saw this post that confirms what I have suggested as a possible additional benefit to running TPMS. 

Sensors mounted on metal, bolt in valve stems are more likely to sense the temperature of the metal wheel which will transfer the heat from wheel bearing or brake drag and failure better than they can report the heat generated in the shoulder of a radial tire.

 On a trip I noted that one tire was 20F more than the others.   When fueling the temperature alarm went off at 160F.  The wheel and hub was very hot.   We were 90 miles from the next town, I found a shop that supported Dexter.  They pulled the wheel and drum and one of the brake pads with broken springs fell out.  There was minimum scoring of the drum and they had the replacement brake assembly … it took an hour to fix.  I would not have known this if it wasn’t for the temperature monitor.  And it could have real bad on I-10 in West Texas.

People need to realize that rubber is really a good insulator to heat transfer so the heat generated internal to the tire structure. The hottest spot in radials is at the belt edge which is about 3/8 to 5/8 deep in the tire structure. The color thermographic picture in THIS post shows the location of the hottest spot.

The heat generated by the tire in the shoulder can not be directly sensed or reported by your TPMS.

 

##RVT1011

TPMS Comparison TireTraker external vs TST 507 internal. Summary and my opinion

Since March I have been conducting a comparison test of two different TPM systems. When I started in March the Ambients were down near freezing. I completed my comparison at the end of July with the ambient temperature above 90°F.
I started by checking the accuracy of the various sensor pressure readings. The summary of that post indicated there was no meaningful difference between the systems for pressure readings for the 12 sensors I tested.

In THIS post I confirmed the temperature readings were also essentially the same by comparing the morning readings after a night long temperature soak.

The next step was to see what the systems reported for the hot running temperatures. I expected that the numbers from the internal system would be higher than the numbers from the external sensors. The reason for this is that the external sensor is actually reading the temperature of the outer end of the metal valve stem that is wiping around in outside air being cooled. The small collum of hot air inside the valve stem just can't transfer enough heat as fast as the metal (brass) valve stems is being cooled off. Here are the numbers. But I had to wonder if the cold ambients might somehow be skewing the data so, knowing I was planning to travel to Indiana in April, Michigan in June and  Wyoming in July I was hoping that the ambient temperature on one or more of these trips would be significantly warmer than my March trip.

In June I posted my opinion on the value or lack thereof of temperature readings from TPMS. This opinion was not based on any specific results from my testing but just from some serious contemplation to tire temperature recording I had been involved with when working on Indianapolis race car tires and my observations in test laboratories while I worked as a tire design engineer.

Back in May 2012, I posted some actual running temperature images recorded by some high priced laboratory instruments. You can see the results here. Clearly using a handheld IR gun after you come to a stop or depending on the temperature of the air inside the tire, which is obviously an "average" of the hot and cooler areas of a tire, is not going to give you a reading of the hottest part of a running tire. 
If we are concerned about the advanced warning of a tire failure, tire temperature numbers from a TPMS is not going to be sufficiently precise to identify the temperature of the hot spot. While high temperature can lead to a tire failure, the failure will most likely occur at the hottest spot which is not the "average" of the internal surface of a tire. Also, extended periods of time at elevated temperature can contribute to the degradation of rubber which could eventually lead to a failure like a belt separation while never being hot enough to set off the high-temperature alarm.

Finally, in July, I could review the results of my readings with higher ambients of the different readings observed with the internal TST 507 system vs the external Tire Traker system.

In mid-Aug I posted the test results of the external Traker system vs the internal TST system.

OK, so what is the bottom line?

IMO the performance of the two different systems is similar enough to make recommending one over the other impossible.

There is a cost penalty with the internal system of a little over $100 plus any purchase price difference. Looking at the two different web sites I find the 6 sensor Tire Traker system with booster available at $398.  The Truck System Technology 6 sensor internal system with the booster is listed at $599. You will need to figure there will be an extra charge to pay for the dismount, mount, and balance of the internal system. I had the TST system installed locally for $109.07 which would bring my total to $708. 
To answer the question some of you may have. I purchased and use a Tire Traker TPMS in 2009 befroe I started this blog and plan on continuing with that system for the foreseeable future.

The advertisement you see on this blog does not involve me as it is between any advertiser and RVTravel.com

Internal vs External TPMS test results

Previously I posted the test results for my comparison of internal vs external sensor TPM systems. The weather was cool to cold back in March. Now I can report the results with the ambient in the upper 80's.

All temperatures are in °F
Internal System.
RF 102   LF  104    RRO  104   RRI  111   LRI   111   LRO  102

External System
RF  73   LF  75   RRO  71   RRI   71   LRI  82   LRO   80

I was driving 65 mph with cruse on a level stretch of Interstate. The Sun was fully on the left side of the RV.

Difference  Internal - External
 RF  29   LF  29   RRO  33   RRI   40   LRI  29   LRO   22

These results tend to match the previous runs with the internal reporting about 30F hotter than the external sensors.

Again I do not consider the results of a comparison between the temperature readings to be "meaningful" in the sense that the internal sensor numbers are useless.

Suggestion:  If you have an external sensor TPMS I would continue to use that system. Just be aware that the temperature readings are probably in the range of 27 to 40 F cooler than the temperature readings your friend would be getting with their internal sensor system. If you are concerned you could change your High-Temperature warning level with your external sensor system from the factory 158°F to about 145°F.  Just be aware that if in Phoenix or Death Valley or other location where the Ambient exceeds 120°F  you may get a high temp warning. If you do just pay attention to the pressure readings to be sure you are not losing any air pressure.

Since tire temperature is also a function of load and speed you might bump up the High-Pressure warning level 5°F till you are not getting a warning simply because it is hot outside.  Of course, it might also help to slow down a bit as that will also result in lower tire temperature.

Bottom Line:
There is a difference between temperature readings based on sensor location. BUT this does not automatically make one type of system better or worse than another. As I said in THIS post I am not a fan of TPMS temperature readings no matter which type sensor you run.

More on TPMS Temperature reporting

Continuing my series on TPMS.  Last time I covered temperature reports when it was moderate to just cool outside. This report is different. On my way South to GA from OH it got downright cold.
 

I stopped for the night in KY and in the morning I obtained these readings.

Internal System.
RF 30   LF  32    RRO 32    RRI  32    LRI   30  LRO  32

External System
RF  32   LF  32   RRO  32   RRI  32   LRI  32   LRO   32

As expected the temperature numbers were essentially the same. To me this confirms that the sensors can report ambient temperature if given sufficient time to cool to ambient temp.

After about an hour running down I-75 I observed these temperatures when the outside temperature was in the 40's.

Internal System.
RF 86   LF  83    RRO  85    RRI  86    LRI   80   LRO  80

External System
RF  48   LF  48   RRO  46   RRI   44   LRI  57   LRO   55


These numbers clearly show that the external sensors are reporting significantly cooler temperatures than the internal sensors. With cooler ambient the difference internal to external is greater than when the temperatures were warmer. I previously suggested that people running external semsor TPMS might consider adjusting theit high temperature warning level down by 10°F to 15°F.  While the above might suggest lowering from 158°F to maybe 135°F I am not sure if this would be too cool for people that are traveling when the abmient is above 85°F.

For now you might just want to be aware of this difference. I am hoping that later this summer when I am traveling I will be able to get measurements when the ambient is above 85°F.

How accurate is your TPMS - Part two

Last week I posted on the question of "How Accurate was your TPMS".  This week I am continuing on my close examination of TPM systems.

We saw that the variation in pressure readings were Measurable but that IMO the differences were not meaningful.

I recently traveled from Akron, Ohio, to a large (2700+) RV Convention held by Family Motor Coach Association (FMCA) in Perry, GA. There was a large variation in ambient temperature during the trip with a low of 26°F to a midday high of 78°F observed. I felt that this trip was a good opportunity to take a first look at the temperature numbers reported by an internal TPMS vs. an external TPMS.

To start out let's look at the morning temperatures in GA before I started driving home.
 All temperatures are in °F
Internal System.
RF 61   LF  61    RRO  61    RRI  61    LRI   63   LRO  61

External System
RF  60   LF  62   RRO  60   RRI   60   LRI  62   LRO   62

I feel it is reasonable to say that for all intents and purposes the temperature readings are the same.

After heading out on my trip North  I stopped a couple times and recorded the readings.
The ambient temperature was 74.0°F
Internal System.
RF 108   LF  106    RRO  111    RRI  115    LRI   111   LRO  108

External System
RF  80   LF  84   RRO  84   RRI   84   LRI  88   LRO   85

I made a second stop and this time was able to learn the ambient temperature was 60.9°F
Internal System.
RF 95   LF  90    RRO  93    RRI  99    LRI   100   LRO  91

External System
RF  62   LF  68   RRO  66   RRI   66   LRI  73  LRO   71


I consider the above temperature differences to be both measurable and meaningful.

All the above data provides some interesting information.  All along I have thought and said that I felt that the temperature reading from external TPM would be affected and cooled by the outside temperature and rapid air movement around the sensor. Thinking about the heat flow the heat is generated in the outer edges of the belts under the tread in the radial tires. While some of this heat flows out through the tire sidewall the insulating properties slows this heat flow. Most of the heat energy flows into the air chamber where it is transferred to the metal wheel and then to outside air.

An internal sensor mounted on the wheel will be measuring the temperature of the air on the inside of the tire but since the sensor is in contact with the wheel it will be cooler than the hottest part of the tire.
An external sensor is depending on the heat to transfer from the wheel to the brass valve stem and then to the metal base of the sensor and finally to the thermocouple inside the sensor to report the temperature. But along the way heat is being lost to the outside air from the wheel outer surface and through the brass valve stem and from the brass sensor base to the cooler outside air.

BOTTOM LINE
I believe that the default high temperature warning for all or most TPMS is 158°F ( 70°C). With this initial data I plan on suggesting that the high temperature warning for external sensor TPMS be lowered by 10°F to 15°F.   I will be repeating this temperature comparison later this summer when I travel from Akron to Yellowstone. I will be looking for the numbers when ambient is in the 85°F to 95°F range to see if external sensors continue to be cooled as much at these higher ambient temperatures.