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Old 11-07-2018, 06:33 PM   #1
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Proper PSI

I asked this question in the Flying Cloud section, but perhaps it’s best asked here.

I have a 2018 Flying Cloud 19’ with 15” ST225/75R15 Goodyear Endurance tires. The maximum recommended inflation given in the Airstream manual is 80 psi. The Load / Inflation chart given by Goodyear for the tire is indeed 80psi but if I am reading the chart right, that is with 2830 lbs per tire (2830 x 2 = 5660). If so, the max GVWR for the 19’ is 4500 and again, if I am reading Goodyear’s chart correctly, would 55 psi for 2270 (2270 x 2 =4540) be a more correct psi for my trailer?

https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
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Old 11-07-2018, 08:22 PM   #2
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Originally Posted by tjwoods1 View Post
I asked this question in the Flying Cloud section, but perhaps it’s best asked here.

I have a 2018 Flying Cloud 19’ with 15” ST225/75R15 Goodyear Endurance tires. The maximum recommended inflation given in the Airstream manual is 80 psi. The Load / Inflation chart given by Goodyear for the tire is indeed 80psi but if I am reading the chart right, that is with 2830 lbs per tire (2830 x 2 = 5660). If so, the max GVWR for the 19’ is 4500 and again, if I am reading Goodyear’s chart correctly, would 55 psi for 2270 (2270 x 2 =4540) be a more correct psi for my trailer?

https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
You're going to get two opinions on that. Many run the pressures on the load and inflation charts plus about 10% to allow for uneven loading, however resident tire expert Tireman9 (Roger Marble) is now recommending that trailer tires be inflated to their maximum sidewall markings. Lower pressure will give the trailer a softer ride but due to the shear placed on trailer tires Roger is now recommending full pressure. He does however still recommend using the tables for the tow vehicle tires.
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Old 11-08-2018, 05:53 AM   #3
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Originally Posted by ITSNO60 View Post
You're going to get two opinions on that. Many run the pressures on the load and inflation charts plus about 10% to allow for uneven loading, however resident tire expert Tireman9 (Roger Marble) is now recommending that trailer tires be inflated to their maximum sidewall markings. Lower pressure will give the trailer a softer ride but due to the shear placed on trailer tires Roger is now recommending full pressure. He does however still recommend using the tables for the tow vehicle tires.
A 19', single axle Bambi doesn't experience the same 'tire shear' that a multi-axle trailer does, so IMO maximum PSI is definitely not required.
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Old 11-08-2018, 06:18 AM   #4
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Originally Posted by tjwoods1 View Post
I asked this question in the Flying Cloud section, but perhaps it’s best asked here.

I have a 2018 Flying Cloud 19’ with 15” ST225/75R15 Goodyear Endurance tires. The maximum recommended inflation given in the Airstream manual is 80 psi. The Load / Inflation chart given by Goodyear for the tire is indeed 80psi but if I am reading the chart right, that is with 2830 lbs per tire (2830 x 2 = 5660). If so, the max GVWR for the 19’ is 4500 and again, if I am reading Goodyear’s chart correctly, would 55 psi for 2270 (2270 x 2 =4540) be a more correct psi for my trailer?

https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

Already answered HERE.
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Old 11-08-2018, 06:51 AM   #5
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Parallel threads, which Tireman has already linked:

http://www.airforums.com/forums/f542...-a-189156.html
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Old 11-08-2018, 08:34 AM   #6
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I don't know how I made it through life without ever hearing "interply shear", and now I hear it every day. I love a good term.

You'll drive yourself nuts trying to understand and use inflation charts.
I settled on 65 psi, and watching the TPMS, I did not experience much heat buildup while on the road.
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Old 11-08-2018, 10:36 AM   #7
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Originally Posted by tjwoods1 View Post
I asked this question in the Flying Cloud section, but perhaps it’s best asked here.

I have a 2018 Flying Cloud 19’ with 15” ST225/75R15 Goodyear Endurance tires. The maximum recommended inflation given in the Airstream manual is 80 psi. The Load / Inflation chart given by Goodyear for the tire is indeed 80psi but if I am reading the chart right, that is with 2830 lbs per tire (2830 x 2 = 5660). If so, the max GVWR for the 19’ is 4500 and again, if I am reading Goodyear’s chart correctly, would 55 psi for 2270 (2270 x 2 =4540) be a more correct psi for my trailer?

https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
You have posted a bunch of data that is mostly available on the internet. The one piece that you didn't post is the actual load. (The weight by wheel) Sure the trailer could handle the max GVWR. The question would be is this your actual load? Or is it possible you would load your trailer to the max GVWR?

Once known, you don't want to inflate the tire to meet the greatest load you expect, you want to inflate to exceed that load. By at least 10 to 15 percent. Riding in the edge is an OK thing in some arenas. Just not in the tire capacity arena. If the tires have the ability to handle 10 or 15 percent more, the tire has a better chance of surviving at the place where the rubber meets the road.

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Old 11-08-2018, 03:10 PM   #8
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So I would weigh the trailer - add 15% to that - and then look at the tire manufacturer chart for that inflation recommendation?
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Old 11-08-2018, 03:23 PM   #9
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I’m no tire engineer, but I run my GYEs at 75 on my 27 ft FC. they have been running cool and the trailer pulls smoothly.

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Old 11-08-2018, 03:29 PM   #10
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So I would weigh the trailer - add 15% to that - and then look at the tire manufacturer chart for that inflation recommendation?
Yes -
If you use a P rated tire (versus a ST tire) you will have to degrade the capacity of the tire by 10%.

And you would want to use the heaviest wheel position for the weight as most travel trailers are un-equally loaded.

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Old 11-08-2018, 03:42 PM   #11
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When I got my FC 19’, the label for tire pressure from Airstream says that the recommended pressure is 80 psi, which corresponds to the max tire pressure labeled on the tire. In My 50 plus years as a tire consumer, I have never seen this. Most often, the recommended pressure is in the vicinity of 30% under the max listed on the tire. Mechanics tend to fill tires to the max rating on the sidewall. That pressure usually results in over inflation and excess wear at the center tread. Given the data listed on Goodyear’s inflation/load chart. Why would I not experience over inflation wear if I use Airstream’s 80 psi inflation recommendation.
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Old 11-09-2018, 10:03 AM   #12
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I don't know how I made it through life without ever hearing "interply shear", and now I hear it every day. I love a good term.

You'll drive yourself nuts trying to understand and use inflation charts.
I settled on 65 psi, and watching the TPMS, I did not experience much heat buildup while on the road.

Interply Shear has always been there in radial tires but wasn't anything the operator could do about it till I put the technical term together with a chance observation of a large 5th wheel making a 180° turn in freshly smoothed gravel
PLUS had access to the two different computer programs that helped me understand why the tire path on the trailer was different than the path from non-towed vehicles.
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Old 11-09-2018, 10:07 AM   #13
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So I would weigh the trailer - add 15% to that - and then look at the tire manufacturer chart for that inflation recommendation?

That is the recommendation for motorhomes. My recommendation as a tire engineer for trailers is to inflate to the inflation shown on the tire sidewall (which is also probably the number on your certification lable) and run that inflation. To get better tire life you ALSO need to confirm your actual load is no more than 85% of the load capacity of the tire bases on the inflation you use.


I do cover this in detail in my RV tire blog.


Sorry but I can not post a hot link here.
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Old 11-09-2018, 10:09 AM   #14
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When I got my FC 19’, the label for tire pressure from Airstream says that the recommended pressure is 80 psi, which corresponds to the max tire pressure labeled on the tire. In My 50 plus years as a tire consumer, I have never seen this. Most often, the recommended pressure is in the vicinity of 30% under the max listed on the tire. Mechanics tend to fill tires to the max rating on the sidewall. That pressure usually results in over inflation and excess wear at the center tread. Given the data listed on Goodyear’s inflation/load chart. Why would I not experience over inflation wear if I use Airstream’s 80 psi inflation recommendation.

The center wear was more likely with bias tires. Radial treads do not respond to the same level as bias to inflation.
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Old 11-09-2018, 10:10 AM   #15
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I’m no tire engineer, but I run my GYEs at 75 on my 27 ft FC. they have been running cool and the trailer pulls smoothly.

Mike

And the actual load is what percentage of the tire capacity ar 75 psi?
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Old 11-09-2018, 10:33 AM   #16
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And the actual load is what percentage of the tire capacity ar 75 psi?


I’m not caffeinated but I want to play along as I’m considering the GYEs for spring. On the scales loaded for camping and WD applied, my axles combined see 6000#. Running the GYEs at 65 PSI would provide 2540#/tire or 10,160# total load carrying capacity so the actual load would be 59% of the tires’ capacity at 65 PSI. Am I seeing that correctly??

If so, is there any reason not to run at 65 PSI instead of 80?

Thanks!
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Old 11-09-2018, 10:50 AM   #17
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The recommended tire pressure for my tires is 80psi cold. Once on the road traveling that PSI is going to go up by about 10 to 15%. I think messing around with the tire pressure based upon load is getting just a bit ridiculous and you are asking for trouble. Fill it to the recommended PSI cold and leave it. That means in cooler weather putting more air in and in the summer putting less air in.
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Old 11-09-2018, 11:40 AM   #18
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I’m not caffeinated but I want to play along as I’m considering the GYEs for spring. On the scales loaded for camping and WD applied, my axles combined see 6000#. Running the GYEs at 65 PSI would provide 2540#/tire or 10,160# total load carrying capacity so the actual load would be 59% of the tires’ capacity at 65 PSI. Am I seeing that correctly??

If so, is there any reason not to run at 65 PSI instead of 80?

Thanks!
There may be a flaw. The above assumes all tires are loaded equally. For a TV usually the loading from side to side is pretty close to being equal. The front back or axle load usually differs measurably.

On a travel trailer the loading may be very unequal from side to side and front to back. If all of the tires average 59% there could be one that is 70%. It is an unknown. Sizing tire capacity to the tire position that has the greatest load would be desired.

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Old 11-09-2018, 01:12 PM   #19
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So how does it pull at 80 psi? Does it bounce around a lot? That much pressure would bother me. There is no addtional shear on a 1 axle trailer. So the picture of the 5 th wheel dragging is irrelevant.

I have not idea that there is even a "proper" inflation by definition in this case. I also would try 65 and then go down or up depending upon the results I got.
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Old 11-09-2018, 01:26 PM   #20
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And the actual load is what percentage of the tire capacity ar 75 psi?
I’ll have to find out next spring. 🤔

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