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Old 02-03-2018, 07:45 PM   #29
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Originally Posted by Cowpie1 View Post
Actually, the true industry experts suggest tire cold pressure should be per the tire maker's specs based on the actual load on the tires. Only if they are at maximum loading should they be run at the maximum pressure on the sidewall.
The fallacy in that theory - from the commercial side of the house - is sort of self evident. Do you verify the “load carried” on your tires for every trip? How accurate is your tire inflation gauge? A 1 PSI loss of inflation pressure equates to about a 1.6% loss of load capacity.
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Old 02-04-2018, 07:16 AM   #30
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Originally Posted by FastEagle View Post
The fallacy in that theory - from the commercial side of the house - is sort of self evident. Do you verify the “load carried” on your tires for every trip? How accurate is your tire inflation gauge? A 1 PSI loss of inflation pressure equates to about a 1.6% loss of load capacity.
I use the same tire gauge for all my needs. I have it calibrated occasionally at my commercial tire dealer shop. For a travel trailer, the load would be within a given range that is similar each time. Not like I would be varying the load more than 500 lb, which would be about 125 lb a tire. So the weight of the loaded trailer I established initially would be a good starting point. I have never had a trailer loaded to full GVWR. And I check the tire pressures cold before every trip. Even every morning during a trip if there are major ambient temperature variations. Sure a lot easier than checking all the tires on my commercial trucks, which I do in a similar manner.
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Old 02-04-2018, 09:16 AM   #31
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FastEagle, I do have to agree with Cowpie1. From the Goodyear Endurance pressure vs loading chart for ST205/75R14 tires, @ 50 psi the total load is 7,040 lbs and @ 65 lbs the total load is 8160 lbs. Our trailer has a 3,780 dry weight with a 7,000 GVWR. We probably never exceed 5,000 lbs fully loaded for a trip. We just don't carry that much stuff. That being said, since we never come close to the GVWR, 50 psi is enough according to the chart. However, I feel a little more comfortable airing to 55-60 psi, just me. A real advantage to the Endurance tires is that they have a pretty wide safe pressure rating as long as the pressure is well above the actual load. Of course, all tires should be equal in pressure.

One thing that does concern me is on a light trailer loaded to 5,000 lbs and tires @ 65 lbs, does the hard tire not have as much friction with the road for stopping as well as a tire @ 50 lbs? Does it make any difference?
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Old 02-04-2018, 10:44 AM   #32
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Answer to above.
I would not bother to much about friction for stopping.
More important is that your tires wont overheat.
To give the tire a still acceptable gripp ( and comfort) you can add 10% to the weighed load on it, and calculate the pressure for 160km/ 99m/h. This will give maximum reserve with stiil acceptable gripp.
So your example 7000 lbs +10%= 7700 lbs / 4 tires= 1925lbs .
The tire 215/75R 14 has in LT sort 1820 lbs maxload.
This would EUR calculate a pressure of 69.72 psi rounded 70 psi.
Mayby thats the reason why trailermakers advice max pressure of in this case 65 psi.
Also calculated it for you assumed real weight of 5000+10%=5500
Gave 45.78 psi rounded 46 psi.
So then 50 psi would be OK.

I agree that a traveltrailer once weighed fully loaded , will not chanche in weigt in time.
If so , you will be aware of it, because you added things like a moover with battery or solarpower with battery.
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Old 02-04-2018, 02:31 PM   #33
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Mind that if you do something else then what the vehicle maker prescribes with the pressure, that you yourselfes are responcible.

I am googling dayly for tire-pressure, and recently read that in Norway you now can get penalty points on your drivers-licence, if you go from the prescribed pressure of your vehicle.

I think that a bad development.
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Old 02-04-2018, 05:55 PM   #34
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Originally Posted by Cowpie1 View Post
I use the same tire gauge for all my needs. I have it calibrated occasionally at my commercial tire dealer shop. For a travel trailer, the load would be within a given range that is similar each time. Not like I would be varying the load more than 500 lb, which would be about 125 lb a tire. So the weight of the loaded trailer I established initially would be a good starting point. I have never had a trailer loaded to full GVWR. And I check the tire pressures cold before every trip. Even every morning during a trip if there are major ambient temperature variations. Sure a lot easier than checking all the tires on my commercial trucks, which I do in a similar manner.
I’m just going to add another caveat to this and then I’m out of thread, because your procedures are not standard when compared with tire industry standards.

Statistics from government and private industry sources reveal one consistent fact. Weight across RV trailer axles are almost always different from side to side. To counter that, they recommend balancing the cargo to even out the weight on each end of individual axles. Then, inflate the tires on each axle to the weight of the heaviest end.

Bottom line, if you’re inflating to the basic load carried you probably have at least one tire overloaded. Of course that could happen even when using the vehicle manufacturer’s recommendations when the trailer is nearly overloaded.
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Old 02-04-2018, 08:37 PM   #35
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Good point FastEagle. Minimum tire pressures isn't the best idea here.
Lots of new folks to the trailer world haven't learned the disadvantages of de rating a tire on a trailer with close spaced axles....or the advantage of max sidewall pressures. What ever you know about a car/truck/van/etc with tires at the corners simply doesn't work with close spaced axles.

The biggie is ply shear as the tire side scrubs around a corner or backing up. More pressure helps hold the tire shape = less stress on the carcass plies. As suggested Roger Marble (a tire engineer) rvtiresafety has several articles with all this and more.

While quoting Goodyear lets look at all they say about tire pressures for a trailer:https://www.goodyearrvtires.com/weighing-your-rv.aspx
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..

Now for those that have chosen too much tire for their trailers axle rating I like this from ;
rvsafety.com

Tire Load and Inflation Ratings

Note: Towable – Travel Trailer/ 5th Wheel owners Due to the severe use conditions experienced by tires when axles are very close together – tire industry experts recommend maximum (sidewall) inflation pressure for towable tires unless this causes a sever over-inflation situation (20psi+), often referred to as the ‘basketball effect’. If this is your situation allow a 10 – 15psi safety margin above the minimum required inflation pressure.

Several other website safety blogs have much the same on best pressures for a tire on a trailer.
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Old 02-05-2018, 12:09 AM   #36
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I’m just going to add another caveat to this and then I’m out of thread, because your procedures are not standard when compared with tire industry standards.

Statistics from government and private industry sources reveal one consistent fact. Weight across RV trailer axles are almost always different from side to side. To counter that, they recommend balancing the cargo to even out the weight on each end of individual axles. Then, inflate the tires on each axle to the weight of the heaviest end.

Bottom line, if you’re inflating to the basic load carried you probably have at least one tire overloaded. Of course that could happen even when using the vehicle manufacturer’s recommendations when the trailer is nearly overloaded.
But those industry "standards' are based on the lowest common denominator.... the average idiot who can't think his way out of a 55 gallon drum. This is why we also have so many mandated things on vehicles now. Because folks don't take the time to learn how to do things properly.

But then, in all those millions of miles of commercial trucking under my seat, i have learned a little about how to properly load anything from my pickup, trailers, on up thru my commercial trucks. Balancing loads both fore and aft and side to side is something I have been doing for decades and am very proficient at. only with bulk items like gravel, dirt, etc in dump trailers does balancing not work out so nice all the time. But that depends on who is loading the trailer.

No one is hurting my feelings if they choose to go their own way on this. Since it is not my money that is in play, frankly I am not worried in the least what pressure anyone else runs their tires at. I do know, however, what I have learned from the tire makers themselves and how that plays out in the real world, I will not be swayed to change the procedures I use regarding this.

So we all win!!! We each do what we think is best and live with the results.
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