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Old 08-10-2019, 05:06 AM   #1
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Tire pressure question

So, I should be grown up enough to know this stuff, but I could use a bit of wise counsel.

"Fortune Cookie" (2014 23D) is fitted with Michelin LTX M/S2 tires (now just into their 4th season).

Another forum member has the same trailer and tires as ours and he runs his tires at 44 PSI. I've been doing the same following his recommendation.

So, getting ready for our annual trip to the Durango, Colorado area, I have all 4 tires at 42 PSI @ 100-degrees F. Since we will be driving over the scorched earth of Texas and New Mexico, I'm think it is probably good to leave those pressures as-is; my thinking is that as the tires heat from rolling resistance, they will soon have higher pressures than the current 42 PSI... and the Switz-recommended 44 PSI.

By the way, the load limit per sidewall is 2,183 pounds @ 50 PSI. The trailer's CAT scale weight (hooked up and packed up) is 4,680.

So, what should I do.

Gratzi!
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Old 08-10-2019, 05:29 AM   #2
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Tire engineers/designers say "always fill tires on towable trailers to the max cold pressure listed on the tire".



I'd put 50 psi in them.
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Old 08-10-2019, 05:33 AM   #3
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Rob,
As you know it to have the same trailer and tires. I also run 44-45psi in them.
I think 42psi will be fine to run in all that heat.

You are waaaaay ahead of the curve having a TPMS system. I would suggest you not over think it and run the 42psi and just monitor tire temp and psi. If the tires are running a little hot add a couple of psi to reduce rolling resistance.
For every 10 degree increase of ambient temperature change a trailer tire's inflation pressure will increase by about one psi.
With that said. Rolling at 42 psi in 120 degree West, TX heat will be the equivalent of rolling at 46 psi on a nice 80 degree East, AL day.
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Old 08-10-2019, 07:50 AM   #4
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My first observation is that Michelin doesn't make trailer tires.
So the inflation chart is questionable.
My advice after reading hundreds of tire advice threads?
Do what you think best.
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Old 08-10-2019, 07:58 AM   #5
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My $0.02 - I used those same tires on my 27FB which saw about 6000# on the trailer axles according to the CAT scales.

Because they’re P(assenger) tires, you need to divide by 1.1 to calculate usable load capacity for them on a trailer application so you actually have about 1985#/tire capacity (or about 7940# for your trailer). I’m sure your 23D sees less than the 6000# my 27FB does so I’m sure you have plenty of load capacity.

Having said that, I always ran the Michelins at 50PSI cold for max towing capacity and even on the hottest roads, they never went more than 30* above ambient temperature and 10-12% above cold PSI (60-62 PSI) according to TST internal wheel TPMS system.

Rode like a pillow.

I’ve recently swapped them out (after 5 years) for the GYE ST tires that have a much better reputation than the GYMs (which was my reason for going with Michelins in the first place).

While I’m happy with the GYEs, I miss the soft, pillowy feel of the Michelins (even at max cold PSI).

All that to say - the Michelins served me VERY well even at max PSI with no ill effects on the trailer. I don’t think there’s a world of difference between 42 and 44 PSI but it seems a long way from 50 to 42 (16% reduction). I understand temps will increase at a higher percentage from lower cold PSI than they would from higher PSI. And they’re meant to take the increase. I’d go with 50.

Happy camping!
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Old 08-10-2019, 09:01 AM   #6
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Just remember that the true expert on this forum, Andy Thomson of CanAm RV, recommends 44 psi for Michelins XL's and he doesn't second guess outside temperatures or road heat. As an aside, he suggests 45 psi for Goodyear Endurance tires on a 25' trailer -- probably the same for your 23 footer.
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Old 08-11-2019, 09:19 AM   #7
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My trailer placard calls for 60 pounds cold on ST tires. The tires are rated 65 psi max on the sidewall. I’m going with GYE this time. Replacing some aged-out cheap trailer tires that were put on by my son after yet another GYM failure several years ago.

I do note the placard calls for load range ‘C’, but all I can get with the GYE tire is load range “D” which should give me some extra margin at 60 psi. If I can believe the ratings, I’m looking at 8800 pound tire capacity for a 6900 pound trailer. Lots of margin there.

Will have to watch for tire temperature and trailer vibration and rough ride on the next trip and adjust from the 60 psi placard value as I see how it rides.
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Old 08-11-2019, 03:02 PM   #8
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In case of 1 axle and your tiresto be LT, 54 PSI.
In case of tandemaxle and LT , only 25 psi.
In case of tandem and ST tires 31 psi.
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Old 08-11-2019, 11:52 PM   #9
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My answer was meanth for topicstarter, but looks like answer to topic above of rmkrum

For above , you better stick to 65 psi.
6900 to 8800 looks a large margin, but because of ST tires you can go verry high in pressure before bumping begins.

Calculated it with my extra safe system , and came to 60 psi, wich is maximum reserve without bumping.
For that lowered the 2205 lbs maxload a tire , LI 108 by 6 steps to LI102/ 1875 lbs, to give it the minimum deflection without bumping.
Further , 6900lbs total weight of TT , 65 psi pressure, 4 tires on the road,
If I dont lower maxload so 108 LI filled in 50psi would have been the outcome, but then combination of, yust a little more speed then 65 mph, or lower pressure because of inacurate reading, or a bit more weigt on axles then 6900- 690lbs, and overheating of 1 or more tires.
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Old 08-12-2019, 12:24 AM   #10
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Tire pressure question

I made a slight error. The Airstream tire placard says 50 psi. That said, I typically ran 65 psi because it’s a dual axle trailer, and yeah, it does not seem to pop rivets or scramble stuff. So 60 psi seems reasonable...Click image for larger version

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Old 08-12-2019, 02:15 AM   #11
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Can you also give picture of plate beside of that , it probably gives GAWR, GVWR. And do you use a weightdistribution hitch, that would give more.weigt on the axles, and would yustifi an even higher pressure.
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Old 08-12-2019, 04:02 AM   #12
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Saw that plate on other topic pressure geek.
GVWR 5600, GAWR 2800 EACH.
So not the 6900 lbs you gave. You probably added the 1300 lbs payload to GVWR, but yust need to substract it to give the empty weight of 4300lbs.

So I recalculated for GAWRs max used, for instance when WDH used.

Gave 54 psi, with all the reserves, did not mention I also first add 11,1% to axleweigt to make 90% of loadcapacity used , belonging to the pressure.
This covers unequall load R/ L on the axles, and still no bumping.

So check again ,to comfirm if I now have the right data.

But then you still did not reached bumpingborder, you did not löose rivets , you wrote.
Mayby in time, I can even highen up that border, if I see more of this . Now set it to 80% of loadcapacity, belonging to pressure, wher bumping begins, mayby even 70% would still give no rivets lost.
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Old 08-12-2019, 05:23 AM   #13
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So, back to my original question...

We left home with 44 PSI in the Michelins. We drove our "usual" 190 miles to get out of the Fort Worth area on Sunday afternoon so as to miss the Monday morning traffic.

It was darned hot. Much of the way the ambient temp was between 105 and 107. The TPMS reported tire pressures building to 48 to 49, with a couple of brief pressures of 50.

Tire temps never exceeded 111.

I'd say we did good.

Off to Santa Fe today.
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Old 08-12-2019, 05:37 AM   #14
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Quote:
Originally Posted by RFP View Post
So, back to my original question...

We left home with 44 PSI in the Michelins. We drove our "usual" 190 miles to get out of the Fort Worth area on Sunday afternoon so as to miss the Monday morning traffic.

It was darned hot. Much of the way the ambient temp was between 105 and 107. The TPMS reported tire pressures building to 48 to 49, with a couple of brief pressures of 50.

Tire temps never exceeded 111.

I'd say we did good.

Off to Santa Fe today.
Safe travels Rob. Enjoy the trip!
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Old 08-12-2019, 05:40 AM   #15
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Safe travels Rob. Enjoy the trip!
Thanks, Ronnie ! So far, real good...
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Old 08-12-2019, 05:46 AM   #16
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Quote:
Originally Posted by RFP View Post
So, back to my original question...

We left home with 44 PSI in the Michelins. We drove our "usual" 190 miles to get out of the Fort Worth area on Sunday afternoon so as to miss the Monday morning traffic.

It was darned hot. Much of the way the ambient temp was between 105 and 107. The TPMS reported tire pressures building to 48 to 49, with a couple of brief pressures of 50.

Tire temps never exceeded 111.

Id say we did good.

Off to Santa Fe today.
Yes, you did good.

I've been using the Michelins on our '72 since '12 I believe. I'm on a second set. Great tires with no issues. In any case, there is a long thread about the Michelin LTX MS2 (now Defender LTX I think) and a tire engineer, Capri Racer, explained about maximum load carrying capacity being reached at 41psi on "Extra Load" tires, so I've been running mine at 42 PSI.

Also, I do believe the recommendation is to INCREASE cold inflation pressure in high ambient temperature or high speed use.

If you want some good information on tires, Capri Racer's website "Barry's Tire Tech" is a wonderful resource.
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Old 08-12-2019, 06:38 AM   #17
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Why I run the TP I do....🤓

Dual axle trailers=sidewall TP pressure.👍

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Old 08-12-2019, 07:18 AM   #18
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Quote:
Originally Posted by RFP View Post
So, I should be grown up enough to know this stuff, but I could use a bit of wise counsel.

"Fortune Cookie" (2014 23D) is fitted with Michelin LTX M/S2 tires (now just into their 4th season).

Another forum member has the same trailer and tires as ours and he runs his tires at 44 PSI. I've been doing the same following his recommendation.

So, getting ready for our annual trip to the Durango, Colorado area, I have all 4 tires at 42 PSI @ 100-degrees F. Since we will be driving over the scorched earth of Texas and New Mexico, I'm think it is probably good to leave those pressures as-is; my thinking is that as the tires heat from rolling resistance, they will soon have higher pressures than the current 42 PSI... and the Switz-recommended 44 PSI.

By the way, the load limit per sidewall is 2,183 pounds @ 50 PSI. The trailer's CAT scale weight (hooked up and packed up) is 4,680.

So, what should I do.

Gratzi!

1. Have you confirmed the load is evenly split between the four tires? I bet they are not, so you can't simply devide by 4


2. People need to stop being conserned about the HOT pressure or depending on tire heat to increase the pressure to what is needed at a minimum to support the load. The ONLY inflation number people should be talking about or considering is the "COLD" pressure. This is the pressure in the tires when they have not been driven on or in direct sunlight for the previous two hours.
3. Have you read and understood THIS post?
4. There are a couple of blogs, on the Internet written by actual tire engineers on RV Tire Safety and RV tire Technical info. I bet few on the AS thread have read many or any of that information.
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Old 08-12-2019, 07:26 AM   #19
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Yes, you did good.

I've been using the Michelins on our '72 since '12 I believe. I'm on a second set. Great tires with no issues. In any case, there is a long thread about the Michelin LTX MS2 (now Defender LTX I think) and a tire engineer, Capri Racer, explained about maximum load carrying capacity being reached at 41psi on "Extra Load" tires, so I've been running mine at 42 PSI.

Also, I do believe the recommendation is to INCREASE cold inflation pressure in high ambient temperature or high speed use.

If you want some good information on tires, Capri Racer's website "Barry's Tire Tech" is a wonderful resource.

From the other tire engineer:


Yes Capri has great info, even if he worked for a different tire Co 😊


tire pressure needs to be set when tires are at AMBIENT temperature (not warmed up). That is the proper "cold" inflation.


Now it is possible to increase the cold number a bit if you are planning on running in extreme heat BUT if you are doing that then it is possible that your"cold" inflation number isn't as high as it could/should be in normal temperature situation.


What you do not want to ever do is to bleed off the hot pressure. Tires are designed to tolerate the higher pressure as long as the cold pressure is set correctly.
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