Tire pressure and tire temperature questions

[Stewball]

We recently purchased a previously owned 2015 FC28 with 15" Goodyear Marathon D-rated tires. On our first trip (total newbies) we arrived at Canopener 2017 and installed our Forum-recommended TPMS only to find out we had towed our "new" AS from the Carolinas to the Florida panhandle with 40-41 pounds of air in each of our four 65 pound rated tires (confirmed by an accurate tire gauge). We immediately inflated them to the correct 65 pounds.
Question 1: the Goodyear RV tire brochure link in another thread says that tires that are 20% under inflated should be considered flat and should be inspected by a tire professional. Are we in danger? Our four tires were each 20+ pounds under inflated (definitely more than 20%).
Question 2: what should be the pressure and temperature at which we should become concerned as reported by the TPMS? In other words, how hot is considered normal and how low or high should normal pressure be on the road?
Thanks in advance for any responses to these questions or any other relevant advice you might have to offer.

[Boxite]

Boy, Oh Boy! Are you gonna be inundated with replies that tell you your Marathons were already in danger by pedigree from the moment they were mfr'd.

If you don't feel comfortable inspecting them yourself, air them up properly and take them by a tire store and have their technician look them over for signs of separation and scalloping. If they look OK... they probably are.
IMO.

[Naper]

Yes have them looked at by a professional. If these are the original tires they should be replaced. As for pleasure 65 is the maximum recommended, I ran my GYM's at 55 never had a problem.

[paiceman]

Stewball:

I would have them checked if they were mine.

The TST monitoring system we have on our trailer has a preset high temp warning and a low temp warning as well as pressure. When either is reached the display in the truck beeps. It's simple to adjust the settings to what you want and the instructions that came with the system explained at what temp most tire failures occur.

Bud

[GCinSC2]

Stewball,

Yup, hot topic. Studying this tire concern will be in order. Not sure how you inspect for this but if CapriRacer or Tireman9 answer, listen to them. They are tire experts by profession.

Greetings from Hartsville.

Gary

[Dexterpix]

To answer you question about pressure and temp.

I run the "deadly ST tires" that came with my 2014 FC25. When inflated to 65psi to start a day at highway speed I reach 70 -71 psi when the tire heats up. (this has been consistent from day 1) I also see a temp that runs 5-10 degrees over the ambient air temp. (sunny side closer to 10 degrees above, shaded side closer to 5). Rain will drop the temp down to almost ambient air temp. This has also been consistent from day 1.

I think knowing what is normal, based on your driving and loading of the trailer, is more important than an arbitrary number. Set you pressure as advised by the manufacturer and monitor the norms so you will see the little changes before they become a problem. I set my warning alarms at 75psi and 110 degrees for temp.

I have only hit the PSI alarm once after coming down from staying at 9500ft @ 35 degrees temp in Colorado, were I inflated to 65psi, but when I came down to less than 5000ft and 70 degrees my pressure started to climb up to 75psi across all 4 tires.

I have only seen 100+ degrees on the tires 1 or 2 times with ambient air at 95 degrees.

Safe Travels

Joe D

[CapriRacer]

First, we are talking about a fatigue situation - meaning, the damage you caused will not be apparent for quite some time.

Did you cause damage? Most assuredly!

Are you in immediate danger? No.

What you should do is inspect your tires BEFORE every tow. Run our GLOVED hand around the circumference of the tire and feel for bulges. Check the pressure BEFORE every tow.

On your next tow, check the pressure buildup - that is check the pressure before the tow at highway speeds (over 50 mph), and about 1 hour into the tow. If you have enough pressure, the buildup should be no more than 10%. If it is more, get more pressure in the tires, even if it means exceeding the max of 65 psi by as much as 10 psi. Alternatively, you could slow down!

Frankly, I think EVERY trailer owner ought to do these things, but in your case, Stewball, it is a way of being ahead of the pending failure.

Also, you should replace those tires early - say 4 or 5 years.

[overlander63]

Stew, I'd keep an eye on the tires. You're not in imminent danger of losing a tire, but watch them. I know they were inflated properly when we took that trailer in for resale, and it hasn't been that long (mid-November, IIRC). They will normally lose up to 2psi/month, plus rising and dropping temps will also raise or lower the pressure, as well. I've learned the outdoor temperature changes will also cause a tire to lose some pressure, as well.
We do get trailers in regularly with 30-35psi in the tires, and there are no problems after we inflate them to the proper pressure. They've gone on to the normal end of their service life without failure. "Normal" being a 5-6 year life span from date of manufacture stamped on the tire. There are several of us that can tell you how to check tire dates, but the short version is, there will be a four-digit number in an oval stamped in the sidewall of the tire, for example "0415". That would mean the tire was built during the 4th week of 2015.

I'll add the voice of experience to the above post. I learned very early in the era of steel-belted radial tires to not handle them without gloves. a steel cord you didn't see really hurts when you grab it with your bare hands.

[tvketchum]

My opinion, yes, have the inspected. Tread separation will be the primary concern. Also, have the tire shop show you how to identify the date code, as four years is the life expectancy of ST tires. Trailers will sit for extended periods, so the lack of tire rotation cause dry rot to accelerate. Moving down the road will churn the tire compounds, keeping them more pliant and flexible.

Hopefully, you are good. Our plan so far is working with our tires. Monitor system installed (set max pressure about 15% above the tire max pressure, temps can be 150 or so), low pressure alerts on those GYM should be 58 lbs to 55lbs), check with tire gauge, covered when parked more than 3 or 4 days (sunlight will rot tires which don't rotate for long periods), and a new pair every two years installed on the rear axle, with those rear axle tires moving to the front axle, and the better of those two being discarded goes to the spare. Of course, tire stores will not admit new tires are magnetic, so don't be surprised when a new tire picks up a nail and goes flat.....


Sent from my iPhone using Airstream Forums

Tom

[Alluminati]

We have irrational fear that over-inflated tires are going to *POP*. Unless they are way, way, way over-inflated, that will never happen.

Tire pressure numbers are always COLD. Bring your tires up to PSI BEFORE you drive. When your tires are warm, they should be well above the PSI they were when cold; well above your target pressure. This is correct. Do not let pressure out of warm tires. You will do more damage under inflating than you will with over inflated. Tires overheat when they are under inflated.

You don't have to pull out the pressure gauge at every stop, but sometimes a quick hand on the tread will alert you to a problem if one tire is hotter than others.

[Jacob D]

Originally Posted by Stewball

We recently purchased a previously owned 2015 FC28 with 15" Goodyear Marathon D-rated tires. On our first trip (total newbies) we arrived at Canopener 2017 and installed our Forum-recommended TPMS only to find out we had towed our "new" AS from the Carolinas to the Florida panhandle with 40-41 pounds of air in each of our four 65 pound rated tires (confirmed by an accurate tire gauge). We immediately inflated them to the correct 65 pounds.
Question 1: the Goodyear RV tire brochure link in another thread says that tires that are 20% under inflated should be considered flat and should be inspected by a tire professional. Are we in danger? Our four tires were each 20+ pounds under inflated (definitely more than 20%).
Question 2: what should be the pressure and temperature at which we should become concerned as reported by the TPMS? In other words, how hot is considered normal and how low or high should normal pressure be on the road?
Thanks in advance for any responses to these questions or any other relevant advice you might have to offer.

Welcome to Air Forums. There are numerous threads in Air Forums expressing a variety of opinions about tires for your Airstream. Some are thoughtful and well reasoned and some are just bunk. Consider the credentials of the person whose opinion you are reading. I am no expert but true tire experts have posted in some of the threads. My advice is consider the source and do your own homework.

I have lived and worked most of my life in South Carolina. My family has camped in the same '67 Airstream for about 50 years. I have run GYM's for 15 years and have gotten excellent service and performance running no higher air pressure than 45psi. There are some good reasons for running ST tires.

If you want to soften the ride your trailer is subject to you should weigh your rig to determine properly the correct air pressure. The GoodYear web site or any GY dealer can show you a chart that has the pressure your tires need to carry your load. There is never anything wrong with running the 65psi recommended pressure unless your load exceeds the maximum load capacity of the tire. If you need a higher pressure you will have to go to a higher load range tire. All the information you need to know about your tires is on the sidewall, though it is sometimes hard to read.

Most folks in the know about tires recommend replacing based on age. I didn't know that and ran my first set of GYM's for 13 years before I noticed some uneven wear on one tire. My second set will probably be replaced after 6 years.

[franklyfrank]

Originally Posted by Stewball

We recently purchased a previously owned 2015 FC28 with 15" Goodyear Marathon D-rated tires. On our first trip (total newbies) we arrived at Canopener 2017 and installed our Forum-recommended TPMS only to find out we had towed our "new" AS from the Carolinas to the Florida panhandle with 40-41 pounds of air in each of our four 65 pound rated tires (confirmed by an accurate tire gauge). We immediately inflated them to the correct 65 pounds.
Question 1: the Goodyear RV tire brochure link in another thread says that tires that are 20% under inflated should be considered flat and should be inspected by a tire professional. Are we in danger? Our four tires were each 20+ pounds under inflated (definitely more than 20%).
Question 2: what should be the pressure and temperature at which we should become concerned as reported by the TPMS? In other words, how hot is considered normal and how low or high should normal pressure be on the road?
Thanks in advance for any responses to these questions or any other relevant advice you might have to offer.

For your consideration:
TPMS doesn't help you in the event of a thread desperation.
It happens without warning, suddenly and will cause extensive damage.
It happens inspite of you maintaining pressure religiously before and during
a trip. I had TPMS and was obsessed about maintaining tire pressue.
My tire had one and a half seasons, no more than 10,000 miles on it.
I was in the middle lane on an Intersate going 65 MP mostly less.
By the time I was able to move off to the shoulder the trailer got damaged
to the tune of $ 9,400.00 not counting the tire replacement.
It took two round trips and 2 weeks to JC to get the trailer repaired.
Two days lost to get the tires replaced.
I could have avoided all this had I paid attention to all the horror stories, there was even a YouTube video I watched about GYM thread separation.
I thought 2 year old AS relatively new tires I should get at least one more year out of them. It didn't work out that way.
I could have avoided the entire nightmare by dumping the GYM right away and installed the Michelin LTX tires as soon as I read the first story instead of rationalizing it to my regret.
It is one less thing to have anxiety about while trailering.
I tried to attach the pictures but for the life of me I can't get it done.

[jadatis]

The question is if you had underinflated tires for the load on them.
I am able to calculate an advice pressure for your situation.
But need Gross axle weight ratings ( GAWR) of your vehicle ( is it traveltrailer or car?).
Then if for instance my calculated pressure is 40 psi , then you not even had to low pressure , and your tires are save.
So first determine the real needed pressure for your vehicle, and then we can see if you realy had to low pressure .

Need to know from tires 3 things.
1> maximum load or loadindex
2> Loadrange or AT-pressure.( you write D-load LRD so probably 65 psi)
3> speedcode of tire.(letter N = max 140km/87m/h , Q= max 160km/99m/h)
If you give exact sises of tire I can google but reading it from sidewall is more trusted.

Then if we determined the needed cold pressure , it is officially given for when ambiënt temp is 18-20 degr C/65-68 degr F, and I can give a list for what it then will be at lower and higher ambiënt temperature.
cold pressure is when inside tire temp = outside tire temp)

[wvstreamer]

It is so important to just be observant. Easy to feel tires and hubs when you pull in for fuel or at rest area. You'll notice a temp difference just by touch and it can tell you many things about bearings, brakes, and tires. A look and feel takes maybe 20 Seconds. When I drove 18 wheeler it was habit at every stop. It catches trouble before it bites you. Makes the drive much less stressful.
Dave ok

[Stewball]

Thanks so much to each of you for your valuable comments and suggestions. The Airstream community in general and these forums in particular just reinforce our opinion that the AS nation is the most giving and knowledgeable group of RV enthusiasts out there and we are proud to have become members. Our immediate goal is to closely monitor the TPMS and have the tires professionally inspected. One more question I have is: what does "ST" mean? Thanks again to each of you!

[overlander63]

Originally Posted by Stewball

One more question I have is: what does "ST" mean? Thanks again to each of you!

ST= Special Trailer.

[HiHoAgRV]

According to the Goodyear Marathon pressure chart, your tires at 40 psi, are rated to carry 1880 lbs each. As long as your trailer weighs less than 7200 lbs, you should be just fine.

[jadatis]

ST stands for Special Trailer .
And this is the "american " version of "for trailer use only".
ST is calculated in its maximum load for 65m/104km/h and so more deflection allowed , wich gives larger surface on the ground, so more load to carry with the same pressure as an LT-tire( USA) or C-Tyre( EUR).
Also often they have less thick profile to give less isolation to the parts that get the hottest , and because TT's mostly make lesser miles this still gives the tires a good livetime.

But that is why I lower the maximum load or loadindex before I put it in my made calculator for TT's ,to give it the same deflection an LT-tire would have.

"For trailer use only " is mostly N speedrated so maximum speed and the speed the maximum load is calculated for is 140km/86m/h.
They mostly have 2 Loadindex steps higher then same sise and loadrange/plyrated C-tyre.

This maximum load for speed thing I once sorted out in topic on this USA RV forum.

http://forums.goodsamclub.com/index....d/27477930.cfm

Sorted it out when writing so is in the beginning a bit confusing mayby.
Basics is that for every 10km/6.5m/h other speed , 1 loadindex step different as rule of thumb, for higher speed lower Loadindex, lower speed> higher loadindex.
So For ST tires wich are calculated in maxload for about 105 km = 55km lower then 160km/99m/h for wich most C/LT-tires are calculated, you have to substract 5.5 LI step to get the same deflection ( so heatproduction) as an LT /C-tyre would have.

[greghoro]

As far as temperature monitoring, if you have external (valve mounted) sensors, the temperature reported will be somewhat lower than the actual tire air temperature

See the following blog thread by Roger Marble (aka tireman9) for a more detailed explanation

Greg

[Jacob D]

Originally Posted by overlander63

ST= Special Trailer.

As a previous poster said, ST means "Special Trailer" or for trailer use only. The side walls of the tires are beefed up to be able to withstand torque or twisting pressure between the road and the wheel rim. This occurs when making sharp turns (esp when backing up) with dual or triple axle trailers, bouncing off and over curbs when turning sharp corners and on rough roads in general such as might be encountered when boondocking or traveling through construction areas. If you observe a dual axle trailer in a sharp turn you will notice that the trailing tire is actually dragged sideways hence the need for a stronger side wall. This, in my observation, is magnified when backing a trailer into a tight turn . Even the tires on a single axle trailer are subject to fairly substantial sideways pressure when backing into a turn.