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Old 06-24-2015, 11:06 PM   #1
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Trailer tire pressure vs. Heat

So I will begin with my question and then go into some back ground. I have always maxed my tire air pressure out when cold(as advised) however obviously pressure in the tire rises with elevation and temperature(usually temperature falls with elevation negating this effect). So knowing I fill my trailer tires to max and knowing they will get hot and gain pressure how much pressure is too much? I don't have a TPMS (i will soon!)
now the back ground: So a few days ago I set out across the country with my F350 fully loaded and my flatbed trailer with my wife's jeep on it. Total weight was 18.4k with the front axle at 4,800 lbs rear at 6,100 lbs. And the two trailer axles at 7,300lbs. Based on what I'm carrying I figured I have about 17% tongue weight (more than I wanted -but better than too little) with two 5k lb. Axles and 2500lb relatively new towMasters I thought I'd be alright. On the second day after maxing the tires out at 65# in the morning i had a front tire blow on the trailer. Now it was about 85-90degrees and I had gone from almost sea level to 8,000 feet and was on my way back down when it happened. When putting the spare back on I checked the other three tires and they were at 78 psi! Now I know they should be high because the directions on all tires ever is to fill when COLD but at some point it has to be too hot out not to let some air out right?! Anyway I left them and slowed down a little and have been alright since. Plan is to drive through death valley tomorrow and I am a little concerned. I have rearranged the trailer a little since in order to take some weight of the front trailer axel as I think it might be slightly over loaded. Anyway I haven't been able to find much good information on this. Maybe some of you guys with tire pressure monitoring systems (and have thousands of miles starring at them) have the data that will help me out. I wish I knew what the temperatures were but I don't have a system yet.

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Old 06-25-2015, 06:15 AM   #2
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Welcome to the forum.

I don't have the specific answers you're looking for but I can tell you what I think I know.

The tires with less air in them get hotter than the ones with more air. Having an IR/laser thermometer makes quick checks easy. If one of the tires is hotter than the others it's probably low on air.

I'm sure someone will be along to help more soon.

Good luck and stay safe!

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Old 06-25-2015, 07:43 AM   #3
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Originally Posted by Frdrcng97 View Post
relatively new towMasters I thought I'd be alright.

I think this is your real problem. If those are made by the same company as TowMax, they are awful tires. They change the name regularly because they have such a bad reputation. You may want to check.

It is normal for the pressure to go up as tires heat up. My 110psi tires will go up to about 117psi on a 85 - 95 degree day while traveling according to my TPMS.
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Old 06-25-2015, 07:47 AM   #4
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I air trailer tires to max on the sidewall and certainly don't air down because its summer. Manufactures factor in air temperature (I hope).

IR guns from Harbor Freight are inexpensive and work just fine. Be fun to have in Death Valley. Have plenty of drinking water with you.
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Old 06-25-2015, 08:14 AM   #5
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Maximum tire air pressure while professed by many people is not the correct pressure to use.

The recommended pressure is determined by the weight actually being carried by the tire and the tire manufactures inflation chart for that specific tire.

If you notice the original label on your trailer or car does not recommend maximum but instead something lower. This is because it was based on the specified weight and the original tire inflation chart.

While this is a Goodyear document, it does explain the correct way to determine your tire pressure.


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Old 06-25-2015, 08:36 AM   #6
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From Discount Tire:

  • Always inflate trailer tires to the maximum inflation indicated on the sidewall.
  • Check inflation when the tires are cool and have not been exposed to the sun.
  • If the tires are hot to the touch from operation, add three psi to the max inflation.
  • Underinflation is the number one cause of trailer tire failure.
Load Carrying Capacity

  • All tires must be identical in size for the tires to properly manage the weight of the trailer.
  • The combined capacity of the tires must equal or exceed the Gross Vehicle Weight (GVW) of the axle.
  • The combined capacity of all of the tires should exceed the loaded trailer weight by 20 percent.
  • If the actual weight is not available, use the trailer GVW. If a tire fails on a tandem axle trailer, you should replace both tires on that side. The remaining tire is likely to have been subjected to excessive loading.
  • If the tires are replaced with tires of larger diameter, the tongue height may need to be adjusted to maintain proper weight distribution.
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Old 06-25-2015, 09:16 AM   #7
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The Goodyear Tire download is from 2010. The 2014 is a bit different.
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Old 06-25-2015, 12:38 PM   #8
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How fast were you going? You mentioned slowing down and being ok afterwards. Centrifugal force builds heat in tires too. Most trailer tires are rated for 65 mph. What is the weight capacity of the tires? My trailer calls for load range D, but I payed extra and upgraded to load range E to have a cushion buffer instead of having a trailer loaded to the max of the load range D tires.
How old were the tires too? Older tires can't flex as well as new tires. There is a 4 digit code on the tires sidewall. Anything over 6 years is pushing the life expectancy of trailer tires.
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Old 06-25-2015, 02:19 PM   #9
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The high pressure when descending from mountains , can be because of the heat of the brakes, transported trough the rimms.
If you filled the 65 psi at sea level at 65degr F, the 78 psi would mean a temperature in the tire of 150 degrees, the hight does not have that much effect.
About normal warm inside tire temp is 110-115 degr F.
Incidentially the tire inside can get 212 degr F by that braking, yes thats boiling point of water at 14.5 psi outside pressure .

But I also have to know more about the tires of trailer and car.
You already gave the weights on axles and tongue weight of 17 % , wich is higher then allowed as far as I read because 15% maximum to law, but correct me if I am wrong, I am Dutch.

but lowering the pressure you did is totally wrong, this means more deflection for the temperature so more heat production of the tire itself by driving .

And how did you determine the weights , if this is by estimation , you will see that your estimation is to low if you realy weight the axles or better seperate wheels.

This could also have courced the damage to the tire wich gave blow out when extreme situation. Mayby even you should have used even higher cold pressure at 65 degr F then, what you think is maximum pressure.

The AT-pressure of yours 65 psi is not the maximum pressure of a tire.
The maximum cold pressure is 1.4 times the AT pressure so yours 91 psi cold . Warm this can get if realy 212 degr F , about 1.4 times as much so, 1.4 x 1.4= 2 times the AT pressure .

Tireman 9 or Capriracer once wrote that tires are tested to stand 2 to 3 times the AT-pressure . So dont worry about the high pressure at times, and even the valves are tested to can stand that higher presure, there are standards for that.
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Old 06-25-2015, 06:11 PM   #10
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Max pressure rating is a COLD rating, not an overall rating. So if it goes up with temp, that isn't an issue. Increased pressure due to the tire's temperature rising is factored in when the manufacturer sets the max COLD pressure rating. You're over thinking it...
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Old 06-25-2015, 06:51 PM   #11
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I set mine at max PSI cold. The tire mfg allows for PSI change due to heat.
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Old 06-25-2015, 08:07 PM   #12
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Goodyear Tire and Rubber .... weighing RVs
Special Considerations

** Unless trying to resolve poor ride quality problems with an RV trailer, it is recommended that trailer tires be inflated to the pressure indicated on the sidewall of the tire. Trailer tires experience significant lateral (side-to-side) loads due to vehicle sway from uneven roads or passing vehicles. Using the inflation pressure engraved on the sidewall will provide optimum load carrying capacity and minimize heat build-up.**

I've seen my LT235/85-16 E tires on many of my fully loaded GN equipment trailers go up to the 94-96 psi on a 100 degree day running at 65-70 mph.

Any thing you need to know about tires on a trailer or tires on another RV check out tireman9 tire blog. Day and days of reading from a actual tire engineer. He knows some thing about tires for trailers other than the usual tire company blather.

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Old 06-26-2015, 12:25 AM   #13
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Wow really appreciate the responses guys! first to answer a few questions The max weight for the trailer tires is 2540lbs at 65 psi and the axle weights are exact(from CAT scales) except I have no way of knowing how the weight is dispersed on the two trailer axles but I'm pretty sure there is more on the front based on how it is sitting and sidewall flex. Also I was going 70 when the third went but had not been for very long, I potentially had been doing significant breaking by dropping several thousand feet in only a dozen miles or so which might explain excessive heat.
I am glad to hear that the build up of excessive pressure is not a problem and that tires are made to handle it. Also very interested in the Goodyear charts as I have never actually seen one of those before. However can it really be better to inflate to that exact specification rather than maxing out? Are you only improving ride quality?
Also I still find the COLD specification a bit vague... As I know tomorrow my trailer tires cold at 8 am. In death valley will likely be at 70 psi because it will be about 95 degrees while yesterday COLD they were 65 at 8 a.m. in Sequoia national forest because it was much colder than 95 degrees... So when I get up tomorrow and they are 70 do I leave them? Sorry I know I'm splitting hairs here but I know these small differences compound over the course of a long hot trip. So I guess my question is, is COLD based on abient temperature of where u are currently driving? Again I'm probably over thinking it as some of you have suggested especially since from the sound of it over inflation is rarely if ever the problem...seems heat is. I really need a TPMS. Is there a 'fail' temperature that you guys look to stay under or is that tire specific? And where do u find that information?
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Old 06-26-2015, 12:42 AM   #14
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Alright I've collected my thoughts:

Person A and B have identical rigs max psi is 65 COLD:

Person A: max's out his tires at 65 psi 200 miles from death valley at an early morning temperature of 65 degrees. He then drives to death valley and pulls over and let's his tires cool completely. Unfortunately his tires come to equilibrium at 75psi COLD because it is 115 degrees where he is at

Person B: wakes up fills his tires to 65 psi in death valley then starts driving

Now we potentially have two people driveing the same rig at the same location at the same time and they both did it right from what I can tell and yet, person A is actually running 10 psi more pressure in his tires? Who is right? Better yet what if person A goes 200 miles to where person B started? Now he is running under inflated tires? He won't know it until the next moring when he checks COLD right? Because whatever pressure he is reading at the gas station is based on artificial heat build up from running. Should person A have over inflated his tires knowing he was going to a colder climate?

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heat, tire pressure

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