Calling all tire pressure geeks...

[Tireman9]

Originally Posted by rmkrum

Placard on the side of my trailer calls for 60 psi on the tires. The original GYM tires are marked as 65 psi max. They were load range ‘C’. They were cause of a destructive tread separation and $4,000 insured damage.

New GYEs are load range ‘D’ and 65 psi sidewall max. I’ll go to 60 then check the table once I get across a CAT scale fully loaded for camping.

Well it seems there was something wrong.
LR-C tires would normally show 50 psi
LR-D show 65 and LR--E show 80.


If you had a LR-C that said 65 psi those tires should have been reported to NHTSA and recalled.



Nothing against rmkrum but I think a mistake was made in his notes.

[rmkrum]

No mistake. Photos, not notes, mental or on paper.

Original GYM tires were marked 65 psi max cold pressure. Replacements were also 65 psi cold max. Ditto the GYEs coming soon, but they are load range D. Still 215/75R14 size.

Tire placard follows:



Note it states LRC as the end of the tire data. Recommended pressure is 50 psi per the placard...I read it wrong.

I ran 65psi cold as marked on the old tires. The GYMs might have been Load Range D, but they are long gone, thank heavens. I don’t see the sense of a LRC tire on this rig. 6900 gross weight as well. Hard to se in this pic.

[r carl]

Originally Posted by Tireman9

NO


Inflation for trailers is different that for the TV. This is because of the Interply Shear in trailer application that is trying to tear the tire belts off.


I suggest you ALL review THIS post on why tires fail.


If you don't know what Interply Shear is then maybe you don't really understand why trailer tires fail.


FYI on my blog you will see that Goodyear agrees with my advice on proper trailer tire inflation.

Yes , just go with the GY Endurance load / pressure table above. I would not be concerned with interply sheer with GY Endurance tires but I would be with china st tires.

[wulfraat]

Originally Posted by Tireman9

NO


Inflation for trailers is different that for the TV. This is because of the Interply Shear in trailer application that is trying to tear the tire belts off.


I suggest you ALL review THIS post on why tires fail.


If you don't know what Interply Shear is then maybe you don't really understand why trailer tires fail.


FYI on my blog you will see that Goodyear agrees with my advice on proper trailer tire inflation.

I stand corrected.

In the above linked post:

"Running a margin of at least 15% between capacity and measured load is a good first step."

I do run above recommended pressure per the GYE chart. My rig weighs out at 7,500lbs on the axles when hitched. That's 1875lbs per tire. Front tires carry more load as we all know, so perhaps 10%+ shift to the front axle - call it 2062lbs / tire on the front.

Chart says 45-50lbs for that weight. Call it 50. I run at 65lbs - that's 30% higher than manufacturer recommended tire pressure.

I felt comfortable with 30% overhead. Perhaps that is not enough?

[nryn]

I’ve assumed that tire pressures should be read with weight distribution applied. Is this correct?

[jadatis]

Originally Posted by nryn

I’ve assumed that tire pressures should be read with weight distribution applied. Is this correct?

No , you can even measure it when tire off the ground, and you will measure the same pressure, as when max weight on tire.

Once tested it, and it prooved that way.

I sended topicstarter a PM , because he has not reacted after his first post. Maybe he has his mailmessage turned off, so is not notified of new messages.

[ROBERT CROSS]

Why I run the TP I do... GYE@70psi cold.

Dual axles=sidewall flex, low TP, more flex...not good.🤓

TETO

Bob
🇺🇸

[Bob662]

Originally Posted by wulfraat

My rig weighs out at 7,500lbs on the axles when hitched. That's 1875lbs per tire.

I suggest this calculation may be incorrect. You should deduct hitch weight from total weight, unless the 7,500 lbs. is from a Cat scale ticket with the trailer attached to the TV.

Of course, about a third of hitch weight is returned to the trailer by the WDH bars, so maybe ignore hitch weight entirely and then you have a built-in cushion.

[wulfraat]

Originally Posted by Bob662

I suggest this is the wrong calculation. You should deduct hitch weight from total weight, unless the 7,500 lbs. is from a Cat scale ticket with the trailer attached to the TV.

7,500lbs is cat scale weight with WD applied. Total trailer weight is 8,450lbs unhitched.

[CapriRacer]

ah ….. Mmmmm ……

I hope everyone understands that the tire load/pressure charts are MINIMUMS, not recommendations.

[Tireman9]

Originally Posted by r carl

Yes , just go with the GY Endurance load / pressure table above. I would not be concerned with interply sheer with GY Endurance tires but I would be with china st tires.

Direct quote from my RV Tire Safety blog
"
Friday, March 29, 2019

It appears Goodyear agrees with me


I have written a number of times on the advisability of running trailer tires at the inflation molded on the tire sidewall.

Some posts dove deep into the science behind the recommendation. I know this can make your eyes glaze over so how about just following what Goodyear says in their RV Tires information web page:

"Unless trying to resolve poor ride quality problems with an RV trailer, it is recommended that trailer tires be inflated to the pressure indicated on the sidewall of the tire. Trailer tires experience significant lateral (side-to-side) loads due to vehicle sway from uneven roads or passing vehicles. Using the inflation pressure engraved on the sidewall will provide optimum load carrying capacity and minimize heat build-up."
end quote





But hey what do I know? Maybe the guy in the next campground knows more about tire science. I only worked as an actual tire design and forensic engineer for 40 years and am court certified as an "expert".

[Whamm511]

Why do newer ASs weigh double or more than older ASs? My 1978 Argosy 30 weighs a little over 4,000# while I have seen weights close to or even above 9,000# for comparable length newer models. Does this mean I should ONLY consider LR-C tires for my rig? Does a LR-D or E provide me any add’l. benefit?

[jadatis]

TM9 wrote:
Unless trying to resolve poor ride quality problems with an RV trailer, it is recommended that trailer tires be inflated to the pressure indicated on the sidewall of the tire.

Now Tandem axle trailers with max on sidewall, often give loosing rivets. So you resolve poor ride quality wit lower pressure.
Also tires turn more around the same centre in curves, so also improved ride quality with lower ( but still safe) pressure.
To the opinion of this amateur tire-pressure geek, the pressure/ loadcapacity-lists of ST tires,even if first 10% added to the acurately determined load on a tire, give lower then safe pressure, my system gives max reserve with still acceptable riding quality.

[Msherw]

Originally Posted by lsbrodsky

I disagree. If those are Load E tires you want to run them near 80. Are they LT tires? While you will see lots of debate on the forum about tire pressure for comfort, the pressure provides sidewall strength. Trailer tires do not turn like car tires and heavy loads are placed on the sidewalls when you turn, especially when backing...look at the skid marks on concrete after you have done a backing turn. I would never run a trailer tire intended for 80 at 55. Many here run somewhat lower than 80 for comfort, though.

Larry

Agree with Larry. If these are Endurance and are sidewall rated to 80psi like mine, I run them 75-80psi to give them expansion room at highway speeds. I pull my Bambi 22FB at 70 mph on most days. This GY specified pressure rating keeps the sidewalls stiff enough to stop lateral motion. The Endurance is an ST and not an LT. LT is built for ride comfort of a tow vehicle. ST is specific for the RV.

I have not read this full thread since it is now 6 pages long. Just my 2 Cents.

[batman]

So funny. Every time we get on the subject of tire pressure. People expound there opinions rather vehemently. Di-spite the true experts (court certified) tire engineers advise. Why ask, you will just look for others here to validate your own opinion and do what you want anyway. Roll on!

-Dennis

[waninae39]

double axles can use lower tire pressure as the 4 tires share the load
single axle need higher pressure as the two tires share the load

i use 70 lbs cold on the 16 Michele tires on my as 22fb sport bambi
the tires can reach 80 lbs or higher while driving

[rmkrum]

To sort of skip to the chase in my personal situation, prior experience with my setup seems to indicate I should run between 50 psi per the tire placard on the Airstream and the max pressure of 65 psi on the tire sidewall. What has changed is that I’m now running load range D tires instead of load range C on the placard.

Several have opined that 60 psi for these tires should be adequate. Tireman9 has the knowledge and expertise in tire engineering that I respect as well. I don’t yet have empirical data on ride quality with GYE tires. In an abundance of caution, I’m going to run at 60 psi to start and watch temperature and pressure rise very carefully. I don’t have a TPMS on these tires yet, so I’m going to use an infrared thermometer to spot check external sidewall temperature for now.

Since we got rid of the GYM tires we haven’t had tire failures. I’m replacing with GYEs because the current off brand Chinese ones have aged out. Externally, they look fine, but that tells me nothing about internal conditions.

I have to move the AS about 80 miles to get the new tires. You can bet it will be with absolutely minimum load in the AS and done at 55 mph or less because of the CA speed limit on towing. I’m replacing all 5 tires, because the spare is a OEM GYM, which is scary enough.

Once I get the new boots on it, at 60 psi, I’ll monitor ride and tire conditions closely and report on the upcoming cross country trip the end of this month.

[ROBERT CROSS]

Originally Posted by waninae39

double axles can use lower tire pressure as the 4 tires share the load
single axle need higher pressure as the two tires share the load

Not necessarily so....My reason for using 70psi cold.

Bob
🇺🇸

[rmkrum]

Double axles get more ‘scrubbing’ in tight turns. I leave a lot of rubber when doing tight turns on hard pavement. It also try’s to tear belts and tire carcass apart (the infamous interply shear issue). Better to run a bit higher pressure to mitigate some of the dual axle issues.

It’s always a compromise when you are dealing with trying to set the correct tire pressure for a particular rig.

And, you can bet there is some interaction between tow vehicle tire pressure, hitch system, and trailer tire pressure. My ProPride system introduces a few more variables in the lateral traction vs weight carrying area. IMHO it takes a little experimentation and measuring things to get it just right. My current Tacoma can do the job if I set things up just right for the loads I’m carrying in the truck and trailer plus how I have the WD set. The nice thing is I can tell if it’s properly tuned...DW takes a nap underway instead of complaining about the rough ride in the cab. Porpoising really bugs her, so I bottom line tune the rig to avoid that oscillating vertical sensation. Keeps peace in the family.

The power WD jack setup helps a bunch with dealing with that problem. Of course, once we go to a bigger Tundra, it’s gonna take a bunch of fiddling to get it right again.

[r carl]

Originally Posted by Tireman9

But hey what do I know? Maybe the guy in the next campground knows more about tire science. I only worked as an actual tire design and forensic engineer for 40 years and am court certified as an "expert".

If you can teach the Goodyear Tire and Rubber Company a thing or 2 please do so and we can believe their tire inflation charts.