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Old 07-09-2014, 10:58 AM   #1
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Tire Operating Temperatures

Ok, this is just for informational purposes, and is not intended to rekindle the ST v. LT tire debate, or anything of the sort.

We just concluded a 900 mile round trip from San Antonio, Texas to Marfa, Texas. Our Airstream is a 2014 Sport 22FB, single axle, with the factory Goodyear Marathon tires.

I religiously checked the tire pressure, and kept it set at the factory recommended 65 lbs. I drove no faster than 60 mph. Really. We drove out on IH 10, and returned on state highway 90. This provided a mix of freeway driving, and state highway driving on lesser quality roads. The outside temperature ranged from 88 degrees to close to 100 degrees. the time between stops was usually about 2.5 hours.

At each stop, I measured the sidewall temperature with an infrared thermometer. The measurement was taken at the center point of the sidewall in 2-3 different places.

The range of readings I obtained was from 118 degrees to 127 degrees. Rarely did it exceed 130 degrees. The hub temperature, measured on the outside "dust cap" was typically around 108 degrees.

Given my understanding of the temperatures at which tire failure occurs, it seems that my readings are well within those ranges.

Again, this is for informational purposes only. Your results may vary.
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Old 07-09-2014, 07:27 PM   #2
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http://www.airforums.com/forums/f438...nt-119498.html

Hi - I started a thread on this recently and got some helpful info.

One reply there discusses the difference between internal and external tire temperatures.

Bottom line, using a TPMS, I've been seeing a very consistent 30 degree internal rise in temperature and a 10% rise above cold pressures. In a recent 2 hour drive in 80 degree weather, my tires ranged from 108-112 degrees and 55-56 PSI (from 50 PSI cold).

My TPMS manufacturer says tires fail at 180 degrees and they recommend keeping the TPMS temp alarm at 157 (or 154? ) as an early warning. So long as I'm not driving in 125 degree weather, I should be good. :-)

Good luck!
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Old 07-10-2014, 06:45 AM   #3
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Just some more info for discussion:

The rule of thumb for decades has been that tires should experience no more than a 10% pressure buildup. That means that the temperature of the air chamber would be about 30F to 40F higher than ambient.

As part of this rule of thumb, 15% is considered the point where action needs to be taken immediately. That's a temperature build up of 50F to 60F.

But the important temperature is inside the tire itself and can not be measure (unless you install a thermocouple in the tire structure - which has been done for experimental purposes). Put another way, measuring tire surface temperatures hasn't been researched enough to develop a correlation to this internal to the tire temperature, so use that with caution.

But the real problem isn't so much the immediate temperature, but its long term effects. While a tire will fail when it reaches 180F, the rubber degrades over time according to the Arrhenius rule: Reactions take place twice as fast for every 10C (18F) increase in temperature. That's why the 10% rule works for the long haul. It limits the affect of temperature over time.
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Old 07-10-2014, 07:08 AM   #4
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I have found every tire manufacture that I have contacted to be very helpful answering questions I have had concerning tires. A source not to be overlooked.
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Old 07-14-2014, 06:07 PM   #5
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To add just a bit more heat on to this ...... pun intended.

I am from Arizona. Ambient temps from 105 to 110 are the norm in the early to mid afternoon and if it doesn't rain (called moonsoon) those temps will hang there for many hours. The interstate and local highways in the area will see surface temps of 130 +. (may be higher) I would assume tires in contact with the road way would pick up some of that heat and it would be difficult to shed that heat. Plus the movement of the tires on the road would generate more heat in addition to the roadway heat that is already there.

Wouldn't that ambient and roadway heat negatively impact tire life?

If ambient heat is 105, I would guess tire temps could be 150 to 160. I have never measured sidewall and do not have the ability to create an internal measurement. And 110 is not anywhere near a record for this part of the planet. Highs would have to be in the 122+ to be considered a record around here.

If that is correct what would be a good remedy for a user in that situation?

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Old 07-15-2014, 01:11 AM   #6
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Quoting from the Goodyear Recreational Vehicle Tire & Care Guide here: http://www.goodyearrvtires.com/pdfs/tire-care-guide.pdf

On page 5, it says the following, among other things:
  • Tire pressure should be checked when your tires are cold and havent been driven more than one mile. The load capacity for a given cold inflation pressure is based on ambient outside temperatures. The pressure in a hot tire may be as much as 10 to 15 psi higher than the cold tire pressure. That means youll only get an accurate reading when you check your tires when theyre cold.
  • Do NOT bleed air from hot tires.
So, I guess if I get worried about my tire temperature and pressure, the best answer might be to take a nice break for a couple of hours to see what the temperatures and pressures look like based on current ambient temps? It's not clear to me how long I have to let my rig sit quietly before I can once again consider the tires to be "cold" (e.g. matching the current ambient conditions). I suppose, empirically, that I could compare the TPMS temps with the ambient temps though that would probably only work if the tires were in the shade.
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Old 07-15-2014, 05:04 AM   #7
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I also live in the Phoenix sauna area.

It would seem logical that faster speeds equals more heat build up in a tire, so perhaps reducing speed to 55 mph on really hot time periods of the day would help keep the tires in one piece.

I vaguely remember that track temperatures on the Indianapolis Motor Speedway on race day in the Midwest reach 130+ degrees with ambient temperatures usually in the 80s. So when the air temps in the Southwest are above 110 degrees, even with the Dill TPMS, I think slower speeds would be wise. Especially if there were a tire failure, slower speeds should result in less damage as it will take less time to stop the flailing.
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Old 07-15-2014, 05:25 AM   #8
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Quote:
Originally Posted by Action View Post
To add just a bit more heat on to this ...... pun intended......
Pun accepted!

Quote:
Originally Posted by Action View Post
.......Wouldn't that ambient and roadway heat negatively impact tire life?.....
And indeed it does. It is well known that AZ is the worst state for tire failures.

Quote:
Originally Posted by Action View Post
.......I have never measured sidewall and do not have the ability to create an internal measurement.....
In a way you do. Pressure buildup. That's where the 10% Rule comes in.

Quote:
Originally Posted by Action View Post
.......If that is correct what would be a good remedy for a user in that situation?

>>>>>>>>>>>>>Action
First, do what you can. Maintain good inflation pressures. Inspect the tires before every tow. Replace the tires regularly. (Needless to say, tires operating in AZ should be replaced sooner than tires operating in, say, MN!)

Second, check to make sure you have properly sized and inflated your tires. The 10% Rule works here: You want no more than a 10% pressure buildup.

And lastly, Speed. Be very aware that speed generates heat in tires.

If you want a more detailed action plan (See what I did there?), let me know. I'll write one up.
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Old 07-15-2014, 08:25 AM   #9
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Capri, I have noted and studied my pressures with TPMS on the TV as well as the AS. I had always lived by the 10% rule and accepted it at face value. The TVs (many of them) all are well within the 10% rule when pressured according to load.

However, on the AS (Michelin LTX MS) it doesn't matter whether I have 70psi, or 75psi, or 80 psi in the tires, I am always between 10% and 12% pressure rise. Last scale reading I was right at 4100 - 4200# per axle.

Speed makes a difference, but I can't figure why pressure seems not to. TPMS accuracy? But it is consistent day to day.

Infra red temps taken at edge of tread at side wall as well as in between tread blocks never gets above 123* or so....even in AZ last summer.

What gives?
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Old 07-15-2014, 08:49 AM   #10
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On a recent trip where I had an LT tire fail on the trailer, my tire pressures were normal (with a 75lb cold, pressures did not rise above 80 measured by TPMS), however I started taking temps with infrared on the side wall of the tires just to check on things after the failure, and I found my TPMS was not accurate. I was seeing a 10 degree temp rise with the TPMS above ambient(external screw-on sending units), but the tires measured on the side wall were going 20 degrees above ambient. And, much to my surprise, the TV tires were going even hotter (25-30degrees), and that with cold temps at 70 PSI. I've since raised the cold pressure in the TV tires to 75 cold.

These temps were taken after hours of driving at 65 +,- MPH interstate. I sure don't want another tire blowout.
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Old 07-15-2014, 09:00 AM   #11
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Hey, I know some of you are serious tire guys, so how about a citation from a tire manufacturer that explains their take on the 10% rule? I'm looking and looking, but all I can find is more stuff in various forums around the Internet. Not a single tire manufacturer so far. Maybe I'm not looking in the right place. So, can we have a citation, please? Thanks!
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Old 07-15-2014, 10:36 AM   #12
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Found a couple of relevant citations talking about expected tire pressure change for every 10 degrees in temp change (e.g. "A good rule of thumb is that for every 10 degrees Fahrenheit temperature change, tire pressure changes about 1 psi.") but still nothing about a "10% rule":
Finally found something that looks useful and mentions a 10% rule, though it's also not a tire manufacturer's site. Again, since it's not from a tire manufacturer, I put the following citation in the "somebody's opinion" category vs. the "documented fact" category:
Would love to see proper citation from a tire manufacturer on this 10% thing.

As I've monitored my TPMS while driving, I've seen it claim that pressures go up by nearly 10 PSI as tire temps climbed, though I never checked to see whether the temp/pressure change matched 10 degrees for each 1 PSI increase. If not, it might mean my TPMS isn't quite monitoring tire temps...given it's out on the end of the stem, it's likely the TPMS sensor reports a combination of tire, ambient and sun-heated temps.

All four trailer tires move up and down the scale together. The sunny side is of course hotter and higher pressure than the shady side, and at a rest stop, they cool off with resulting lower pressures, etc. The spare is always cooler and at a lower pressure (e.g. ambient shady temps) than the operating tires, so I guess I could use it as a control if I focused more on ensuring it is at the same cold pressure as the other tires when I start the day. That might be an interesting experiment.
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Old 07-15-2014, 12:30 PM   #13
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I have an TPMS that measures psi and temp. Last time we were out, one tire was reading low pressure (15 psi low which triggers the alarm), but 100˚ temp. Ambient temp was mid 90's. The other 3 tires were upper 90's to 100˚ and pressure was up about 5 psi. I checked the tire with a regular tire gauge and pressure was up about 5 psi, or about 20 psi more than the Tire Minder was reporting. The tires are 16" Michelin LT's.

One lesson—TPMS may be wrong.

Second lesson—tire gauge may be wrong.

Maybe I need to change the sensor batteries although it appears the tire sensor in question was reporting psi wrong and temp correctly. It could also be dirt in the sensor or I had it too loose or too tight. The sensors are pretty particular about that. I'm wondering if the sensor just reports psi and converts that to a probable temp reading—probably not, but wondering. Also, it appears the sensor measures temp internally, sort of. It is probably more accurate than using an infrared sensor to check the sidewall. Will the tire temp differ from the air temp inside? My guess is the tire will be hotter, but I would not call that an "educated guess".

Third lesson—TPMS systems help, but are not without fault.

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Old 07-15-2014, 01:27 PM   #14
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I had all kinds of electronic navigation aids in my plane, but when all went south, needle ball and airspeed and a compass would save the day. It was important to practice such flight on occasion with a check pilot to be sure I was current in these very basic instrument flying skills.

The Dill TPMS 1506-453 system is great. But the digital temp gage and the digital tire pressure gage are great backups to verify the Dill information at the next stop......
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