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Old 09-03-2019, 03:04 PM   #1
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80 psi vs 65 psi - are both safe in this situation?

2018 Globtrotter
Goodyear Endurance 80 psi max cold pressure
Outside Temp 95+ degrees

With 80 psi cold inflation and the above temps my TPMS system has shown psi to go to 94-96 and tire temps to 115-119. At this psi I get thrown pillows and some popped rivers in my overhead cabinets.

With 65 psi cold inflation I have 14% margin for my load as weighed on the CAT scales. PSI goes to 79 and temps to 104-107. No thrown pillows or popped rivers and a smoother ride.

I figure if the 65 psi cold pressure doesnt exceed my 80 psi readings Im OK. Is this good logic or flawed?
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Old 09-03-2019, 03:32 PM   #2
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The endurance doesn't say "Inflate to 80 psi."
What it does say is, FOR MAXIMUM LOAD, inflate to80 psi."
I don't have maximum load so I use 65. Thinking of dropping to 60.
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Old 09-03-2019, 03:35 PM   #3
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I assume that when a tire manufacturer gives cold pressure guidance they assume the pressures will increase while running and that they factor relatively extreme surface temperatures in mind.

That said, I played with various tire pressures (same trailer, as you know) on my Alaska trip this summer and found cold pressures anywhere between 73 and 77 to be much better for the trailer, even on very, very rough roads. I’d use higher pressures when one or more tanks were full.

Around the Badlands, where temps were about 95 for a few days, I decreased to 71 and resulting running pressures were, if I remember correctly, above 90. I checked as often as I could and nothing seemed awry.

Cold pressures above 77 and things definitely shook around more in the trailer. I was planning on increasing to 80 when I got back to flat land but I haven’t gotten back to flat land yet, and frankly haven’t seen a need.

I am not a tire expert but have read the threads where the tire experts chime in and used that info + observation for my adjustments. This did well by me, I think.
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Old 09-03-2019, 04:46 PM   #4
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We have participating on Air forum at least three true experts -- two (Capri and Tireman) are retired tire engineers. The third is Andy Thomson, at CanAm RV. Andy has tons of actual experience picking up and delivering all sorts of RV's all over North America with a wide variety of tow vehicles, and he has installed thousands of tires on RV's and has experimented with differing tire pressures and their effects on tire longevity and trailer ride. Having read most of the tire posts, at least over the past four years, here's my synopsis:

The tire engineers suggest tire pressures for maximum load -- usually 80 psi. They're right. That pressure minimizes the risk of interply sheer and tire failure. BUT -- they have never commented (that I've seen) on the effect of that pressure on travel trailer ride, failed rivets, thrown pillows, etc. That doesn't seem to be their focus. Their focus is (I believe) tire strength, not ride quality, or even a combination of the two.

Andy Thomson, with enormous actual experience setting up trailers and experimenting with different tires and different pressures, seems to me to focus on ride quality AND enough tire pressure to assure no tire failures. So strong enough; not necessarily maximum strength.

Andy suggests 45psi for GY Endurance tires on 25' trailers and 55psi for those tires on longer trailers. With Michelin Defenders (his favored tire over the GYE), he suggests 44psi. Andy has had great experiences with the Michelin tires; and, so far, good experience with the Endurance, but they haven't been on the market long enough to conclusively recommend them.

So that's my summary of hundreds of posts. If I got it wrong I'm counting on others to correct me. Andy doesn't post a lot, but when he does it's worth paying careful attention to what he says.

As to owners on this Forum -- they seem to use tire pressures all over the place. You can take advantage of the preceding PLUS the tire manufacturers' tire pressure vs. load tables to form your own opinion. For me, I'm in the Andy Thomson camp. But there may be no wrong answer, so long as you are above (plus a reserve) the manufacturers' tire pressure charts, as are the pressures that Andy suggests.
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Old 09-03-2019, 04:52 PM   #5
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I assume that when a tire manufacturer gives cold pressure guidance they assume the pressures will increase while running and that they factor relatively extreme surface temperatures in mind.
Yes.

Before the vehicle is moved, check and adjust as needed the tire inflation pressures.
There is no spec given for inflation on a hot tire.
Adding or removing air on a hot tire is moving to the unknown.

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Old 09-03-2019, 05:07 PM   #6
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Originally Posted by Bob662 View Post
We have participating on Air forum at least three true experts -- two (Capri and Tireman) are retired tire engineers. The third is Andy Thomson, at CanAm RV. Andy has tons of actual experience picking up and delivering all sorts of RV's all over North America with a wide variety of tow vehicles, and he has installed thousands of tires on RV's and has experimented with differing tire pressures and their effects on tire longevity and trailer ride. Having read most of the tire posts, at least over the past four years, here's my synopsis:

The tire engineers suggest tire pressures for maximum load -- usually 80 psi. They're right. That pressure minimizes the risk of interply sheer and tire failure. BUT -- they have never commented (that I've seen) on the effect of that pressure on travel trailer ride, failed rivets, thrown pillows, etc. That doesn't seem to be their focus. Their focus is (I believe) tire strength, not ride quality, or even a combination of the two.

Andy Thomson, with enormous actual experience setting up trailers and experimenting with different tires and different pressures, seems to me to focus on ride quality AND enough tire pressure to assure no tire failures. So strong enough; not necessarily maximum strength.

Andy suggests 45psi for GY Endurance tires on 25' trailers and 55psi for those tires on longer trailers. With Michelin Defenders (his favored tire over the GYE), he suggests 44psi. Andy has had great experiences with the Michelin tires; and, so far, good experience with the Endurance, but they haven't been on the market long enough to conclusively recommend them.

So that's my summary of hundreds of posts. If I got it wrong I'm counting on others to correct me. Andy doesn't post a lot, but when he does it's worth paying careful attention to what he says.

As to owners on this Forum -- they seem to use tire pressures all over the place. You can take advantage of the preceding PLUS the tire manufacturers' tire pressure vs. load tables to form your own opinion. For me, I'm in the Andy Thomson camp. But there may be no wrong answer, so long as you are above (plus a reserve) the manufacturers' tire pressure charts, as are the pressures that Andy suggests.
^^^^^ X2.

I run at ~65 to max 70lbs cold pressure on the GYE on my 30' weighing 7,500 lbs on the axles hitched and wet / loaded. It's personal choice. That's where I personally feel comfortable balancing ride quality with maximum tire protection against interply sheer.
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Old 09-03-2019, 07:12 PM   #7
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Thanks everyone. This is what I was expecting- just wanted confirmation. I used to be on the max pressure camp but have found out towing a RV is a little different than towing a boat (more moving parts!). I feel that 80psi is not the answer and thanks to Wulfraat, Ive figured out the right tire pressure for my TV. Ive just been trying to dial in the RV side of it.

We are beginning a 2 month trip thru Texas and was wondering if any issues on the heat side of the equation. These responses give me comfort with the 65 psi for this trip. Its higher than 1) Andys 55 and 2) gives me 14% margin over the Mfg Load rating. 60 psi gives me 9% margin but with the heat, I will feel more comfortable with 65.

Ive replaced my OEM shocks with Bilstein. Between the shocks and lowering the air pressure, Ive noticed a big difference in the ride. My TV doesnt need the weight distribution as much as it needs sway control. I reduced my washers from 5 to 3 on the Equal-I-zer hitch in an attempt to soften the stiffness of the bars. I will hit the scales to see what difference that made or did not make and make further adjustments, if necessary.
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Old 09-03-2019, 07:29 PM   #8
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Mind those shocks. There are reports of broken mounts with non OEM shocks......
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Old 09-03-2019, 09:22 PM   #9
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i use 56 psi cold(20C) on as 22fb.
i have Michele 16" tires and only 1 axle
when driving the hot(35C) goes up to 65 psi

4500 lbs on 2 tires/1 axle needs each tire has to support 2250 lbs

if you have 2 axle, you can use less psi
7500 lbs on 4 tires/2 axle needs each tire support 1875 lbs

if you have 3 axle, you can use less psi
9000 lbs on 6 tires/3 axle needs each tire support 1500 lbs
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Old 09-04-2019, 06:15 AM   #10
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Quote:
Originally Posted by GOUSC View Post
2018 Globtrotter
Goodyear Endurance 80 psi max cold pressure
Outside Temp 95+ degrees

With 80 psi cold inflation and the above temps my TPMS system has shown psi to go to 94-96 and tire temps to 115-119. At this psi I get thrown pillows and some popped rivers in my overhead cabinets.

With 65 psi cold inflation I have 14% margin for my load as weighed on the CAT scales. PSI goes to 79 and temps to 104-107. No thrown pillows or popped rivers and a smoother ride.

I figure if the 65 psi cold pressure doesnt exceed my 80 psi readings Im OK. Is this good logic or flawed?
There are a few things that bother me.

1) A pressure buildup from 80 psi to 95 psi is almost 20%. The rule of thumb says not to exceed 10% and anything over 15% is dangerous.

2) But using the Ideal Gas Law, a pressure buildup from 80 to 95 psi starting at 95F would NOT result in a temperature of 105F. It would result in 183F - which is way, way too high.

So one of those is wrong. I suspect it is the pressure value as the load carrying capacity at 65 psi results in a 14% reserve.

So plugging that back in to the Ideal Gas Law formula, I get a pressure rise from 80 to 82 psi results in 107F - and that doesn't seem right either.

And that makes me think there is something wrong with ALL those numbers.
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Old 09-04-2019, 06:48 AM   #11
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There are a few things that bother me.

1) A pressure buildup from 80 psi to 95 psi is almost 20%. The rule of thumb says not to exceed 10% and anything over 15% is dangerous.

2) But using the Ideal Gas Law, a pressure buildup from 80 to 95 psi starting at 95F would NOT result in a temperature of 105F. It would result in 183F - which is way, way too high.

So one of those is wrong. I suspect it is the pressure value as the load carrying capacity at 65 psi results in a 14% reserve.

So plugging that back in to the Ideal Gas Law formula, I get a pressure rise from 80 to 82 psi results in 107F - and that doesn't seem right either.

And that makes me think there is something wrong with ALL those numbers.
The original post states 95 degrees ambient temperature. Was the ambient temperature the same 95 degrees when the cold pressure was set and when he towed? Maybe the 95 degrees was the temperature when he was towing, but set the cold inflation psi at a different temp.

For instance, the last time I added air to my tires was done at 68 degrees ambient temperature, 70 psi. By the middle of the day, while towing, it was 93 degrees ambient temperature and 81 psi. More than the 10%, but I assume the 23 degree difference in ambient temp was causing it?
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Old 09-04-2019, 07:12 AM   #12
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Originally Posted by waninae39 View Post
4500 lbs on 2 tires/1 axle needs each tire has to support 2250 lbs

if you have 2 axle, you can use less psi
7500 lbs on 4 tires/2 axle needs each tire support 1875 lbs

if you have 3 axle, you can use less psi
9000 lbs on 6 tires/3 axle needs each tire support 1500 lbs
That's all great. Until you consult the Good Year Inflation chart and it tells you to run at 25 psi.
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Old 09-04-2019, 07:52 AM   #13
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To hopefully clarify, I set the 65 and 80 psi 1st thing in the morning, tire cold. On this trip the 65 psi was at around 66-70 degree temp.

I use the EezTire TPMS. It has a psi and temperature reading. I feel the TPMS is correct as I set the pressure with a high quality air gauge and it is confirmed by the TPMS. That TPMS suggests a high pressure alarm at 20% above the cold pressure. In this case 65 psi + 20% = 78 psi. 2 of the tires hit a high of 79 / 1 hit 78 and the last 77 so I got an alarm on 3 of the 4 tires but it was only 1 psi above the alarm.

I have no way to know if the temp is correct but the temp is is the ballpark of the outside temp when I set it. The outside temp got up to 97 yesterday driving. This morning the tire pressure is at 68 psi cold with outside temp of 75. IMO the psi is a little higher at rest today because the outside temp is about 10 degrees warmer.

I set my TV tires in similar manner re load / etc. they did not exceed the 20% threshold in the same environment. Rear tires were set at 65 and reached a max of 75. Front tires at 60 and reached 70.

One year ago With the RV I was using 80 psi cold and the temps hit 100 degrees. Max psi was 94 but did not cross the 96 psi 20% alarm. 115 degrees was the tire temp as I seem to recall. This was the first time I got an alarm.

I will admit Im not an expert. If I set the tires at max pressure cold, 80 psi, and the tires rise above the 20%, I would think I would be getting close to exceeding the tires capacity. However, if I set at 65 psi and the psi rises to 79 it would appear to still be within the tires capacity.

In cooler weather the tires may rise 6-8 psi max.
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Old 09-04-2019, 08:01 AM   #14
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That TPMS suggests a high pressure alarm at 20% above the cold pressure. In this case 65 psi + 20% = 78 psi. 2 of the tires hit a high of 79 / 1 hit 78 and the last 77 so I got an alarm on 3 of the 4 tires but it was only 1 psi above the alarm.

I have no way to know if the temp is correct but the temp is is the ballpark of the outside temp when I set it.
That's odd. I set my tires at 65 and while driving I see pressures about +9 or 74. I've seen the temperatures to reach 110f. but the pressure doesn't go up much more. The temp actually rises when I stop for gas, which seems counter-intuitive, but I guess the tires stay cooler while rolling.
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Old 09-04-2019, 08:11 AM   #15
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That's odd. I set my tires at 65 and while driving I see pressures about +9 or 74. I've seen the temperatures to reach 110f. but the pressure doesn't go up much more. The temp actually rises when I stop for gas, which seems counter-intuitive, but I guess the tires stay cooler while rolling.
TPMS sensors inside wheel or stem mounted? Mine are stem mounted. When I stop moving the heat transfers from the rim to the stem to the sensor and there is much less moving air to cool it down.
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Old 09-04-2019, 08:46 AM   #16
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Originally Posted by GOUSC View Post
To hopefully clarify, I set the 65 and 80 psi 1st thing in the morning, tire cold. On this trip the 65 psi was at around 66-70 degree temp.

I use the EezTire TPMS. It has a psi and temperature reading. I feel the TPMS is correct as I set the pressure with a high quality air gauge and it is confirmed by the TPMS. That TPMS suggests a high pressure alarm at 20% above the cold pressure. In this case 65 psi + 20% = 78 psi. 2 of the tires hit a high of 79 / 1 hit 78 and the last 77 so I got an alarm on 3 of the 4 tires but it was only 1 psi above the alarm.

I have no way to know if the temp is correct but the temp is is the ballpark of the outside temp when I set it. The outside temp got up to 97 yesterday driving. This morning the tire pressure is at 68 psi cold with outside temp of 75. IMO the psi is a little higher at rest today because the outside temp is about 10 degrees warmer.

I set my TV tires in similar manner re load / etc. they did not exceed the 20% threshold in the same environment. Rear tires were set at 65 and reached a max of 75. Front tires at 60 and reached 70.

One year ago With the RV I was using 80 psi cold and the temps hit 100 degrees. Max psi was 94 but did not cross the 96 psi 20% alarm. 115 degrees was the tire temp as I seem to recall. This was the first time I got an alarm.

I will admit Im not an expert. If I set the tires at max pressure cold, 80 psi, and the tires rise above the 20%, I would think I would be getting close to exceeding the tires capacity. However, if I set at 65 psi and the psi rises to 79 it would appear to still be within the tires capacity.

In cooler weather the tires may rise 6-8 psi max.
What is the tire's capacity? The sidewall stated limit is for cold tire pressure; that does not mean that if it is at 85 hot, you have exceeded any limits. I am sure there is an expert here who can tell you an absolute pressure limit, independent of temperature.
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Old 09-04-2019, 09:49 AM   #17
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I use the EezTire TPMS also on my as 22FB

most times, the pressure/temp is higher on the road side.

i guess that the road side is heavier as that is where the heavy items inside the trailer are located
when i add new addl batteries, i will move them to the right side to balance L R weight
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Old 09-04-2019, 09:58 AM   #18
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According to the Goodyear Endurance chart we run 'Blue Streak' at 65lb -
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Old 09-04-2019, 10:04 AM   #19
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Quote:
Originally Posted by GOUSC View Post
2018 Globtrotter
Goodyear Endurance 80 psi max cold pressure
Outside Temp 95+ degrees

With 80 psi cold inflation and the above temps my TPMS system has shown psi to go to 94-96 and tire temps to 115-119. At this psi I get thrown pillows and some popped rivers in my overhead cabinets.

With 65 psi cold inflation I have 14% margin for my load as weighed on the CAT scales. PSI goes to 79 and temps to 104-107. No thrown pillows or popped rivers and a smoother ride.

I figure if the 65 psi cold pressure doesnt exceed my 80 psi readings Im OK. Is this good logic or flawed?
Here is the tire pressure chart from Goodyear for their Endurance trailer tires - of various sizes of tires and trailer weights, PER TIRE. As I understand it, my 4000 lb, single axle trailer should have around 45psi in each ST225/75R15 tire. Sound right? https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
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Old 09-04-2019, 10:18 AM   #20
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Here is the tire pressure chart from Goodyear for their Endurance trailer tires - of various sizes of tires and trailer weights, PER TIRE. As I understand it, my 4000 lb, single axle trailer should have around 45psi in each ST225/75R15 tire. Sound right? https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
What that chart tells you is that the absolute MINIMUM pressure you should run, IF your loaded trailer weighs 4000 lbs. AND is perfectly balanced side to side, is 45 psi. Since most of us don't weight each wheel independently adding 15% to the actual weight of the trailer gives a good margin of safety. Now at 4600 lbs. the recommendation is 60 psi. Then, if you can run higher psi without causing your trailer any problems, it's not a bad idea.
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