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Old 01-12-2016, 06:44 AM   #1
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Tire pressure

Just replaced my old Goodyear ST tires (6 ply, D rating) with new LT (10 ply, E rating). On the old ST tires, the sticker on the 5er said to inflate to 65 pounds, which was the max pressure for those tires. The maximum pressure on the new tires are 80 pounds. Should I be running the new ones at 80 or something less?

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Old 01-12-2016, 07:19 AM   #2
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I've always heard to inflate to the max pressure which gives you max load capacity. Goodyear probably has a chart that will tell you the load capacity at various pressures.
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Old 01-12-2016, 07:22 AM   #3
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I would run them at the Cold pressure stamped on the sidewall. If you look at the load carrying capacity for comparable LT/ST tire, you find that the LT is de-rated a little less than the same ST.

The sidewall LCC stamped into the tire is computed on the Cold pressure. If you run it at a lower pressure, it reduces that load carrying capacity.

Usually these charts are found on the tire makers website.
Also remember when you change to a higher rated tire, the sticker on your camper that states size, LCC and pressure are no longer relevant.
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Old 01-12-2016, 08:15 AM   #4
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I didn't see the trailer wheel maximum air pressure mentioned by anyone yet.

@ krsmitty Did you check your trailer wheels? Is 80psi OK for them?
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Old 01-12-2016, 01:56 PM   #5
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Quote:
Originally Posted by krsmitty View Post
Just replaced my old Goodyear ST tires (6 ply, D rating) with new LT (10 ply, E rating). On the old ST tires, the sticker on the 5er said to inflate to 65 pounds, which was the max pressure for those tires. The maximum pressure on the new tires are 80 pounds. Should I be running the new ones at 80 or something less?

Thanks,
Hi krsmitty,

I agree with oldmanAZ, first check to see if your wheels are rated for 80PSI. The max rating is typically stamped on the inside of the wheel so you may have to crawl under the trailer to see. My 80PSI rims are stamped with "3,580# MaxRating"

If your wheels are rated for 80PSI, there's no problem setting the tires a 80PSI cold setting. That'll give you the max load capacity of the tire.

However, as norty1 mentioned, it probably would be good to download the inflation table for your tires, to make sure you have the right pressure that will give you the load rating that is right for your trailer & axles.

Hope this helps.
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Old 01-13-2016, 05:38 AM   #6
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First the 65 psi on your ST tires is not the maximum allowed cold pressure.
Even Goodyear nowadays still allowes 10 psi more and adviced it in the past for the same maximum load when driving 75m/120km/h.

ST tires are calculated in their maximum load for more deflection allowed at the lower speed of 65 m/104km/h , but better would be to calculate the pressure of the maximum load they would have if they calculated them for 160km/99m/h. This would give the same deflection an LT tire of same sises and AT-pressure would have, so lesser heatproduction and so saver tires and longer live time of tires.
Probably like this pressure-advice calculated would give higher then 75 psi ( 65+10) and so higher then the tiremaker allowes as cold pressure.
And probably this would mean that your new tires , because about same sises, need that 80 psi ( or even 10 psi above that wich is allowed) to be save with still no unacceptable bumping.

Made a topic about the maxspeed/maxload relation on RV forum , read it and aply it on your old and new tires to see if your replacement was usefull.
RV.Net Open Roads Forum: How to compare tires for replacement and needed pressure

But also I am willing do the calculation for you if you give me all the needed details here.
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Old 01-13-2016, 05:44 AM   #7
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...
Even Goodyear nowadays still allowes 10 psi more and adviced it in the past for the same maximum load when driving 75m/120km/h.
...
jadatis

I didn't know this. Does Goodyear post this info any place on their web site?
If you have a link to where Goodyear states this I would be interested in seeing it.

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Old 01-13-2016, 06:21 AM   #8
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Here the link to PDF of Goodyear.
End of first page and whole second page is about that psi+10 and even for truck tires 20 psi extra allowed.
Mind that this is old information and Goodyear chanched their view about it lately.

https://www.goodyeartrucktires.com/p...dinflation.pdf

But already in the beginning of my tirepressure-story I got a PDF of Semperit/Continental in wich standing still the tire is allowed to have a pressure of 1.4 times AT-pressure ( again not max pressure) to give it 2 times the maximum load.
This would mean for 50 psi C-load 70 psi and for E-load 80 psi = 112 psi cold.
When this 1.4 times AT pressure filled at freesing point of water ( 0 degr C/32 F) and incidentally by the heat of brakes the tire inside temp rises to boiling point of water ( 100 C/ 212 F) the warm pressure inside tire would be about 2 times AT-pressure.

Once read that tires are tested to be able to stand a pressure of 2 to 3 times AT pressure before they blow. So even filled that high and warmed up its still save.

A already damaged tire by to much heatproduction ,so to low pressure for the load, will blow sooner if filled to that high pressure.

Edit: reading back your first comment here about not to exeed the rimms maximum pressure, this also is sayd in the pdf of goodyear.
If rimm says 80 psi max pressure , realise this is also given cold, so when inside tire temp is outside tire temp , and about 18degr C/65F to 20C/68F.
so again then the rimms are tested for the pressure rising to probably 212F/100C.
Sometimes only maximum load on rimms is given.

my idea of reason for this is next.
When max pressure of rimm, then to high pressure pushes the rimm edges that hold the tire apart or bend them .
When to much load on rimm, the rimm is deformed by the weight on it, or goes leaking air troug it.

I would rather risk a rimm deformation then a tire blow out.
Most likely the pressure given on rimm is already conservative so cold pressure can even be a bit higher before damage to it. Also counts for weight.
When rimm would leak it is slowly and mostly gives time to notice it and handle to it.
But when tire damages by driving, you dont notice it that easy , and when it blows it can even cource accident.
I know this is a dangerous conclusion of mine, but yudge for yourselfes.
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Old 01-13-2016, 06:28 AM   #9
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Correction: In my original post I said that the new tires were LT's. They are ST's.

I checked on the rims for some kind of max pressure. I did see where it mentioned max weight, but did not see anything about max pressure. Since the sticker on the 5er said to use 65 pounds with the old tires I assume the rims are good to at least 65 pounds. So, decided to go with 70 pounds for now.
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Old 01-13-2016, 06:46 AM   #10
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... I did see where it mentioned max weight, but did not see anything about max pressure. ...
krsmitty,

What was the max weight rating stamped on your rims?

What type of new ST tires did you get?

What max weight rating are your trailer axles?

This information will help in identifying what your optimum tire pressure is for your trailer and to make sure you're not under pressurizing your tires. Tires with low pressure below load is were the risk of blow outs increase.

Thanks.
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