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Old 03-25-2019, 02:58 PM   #101
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Endurance Tire pressure on 27FB Int'l

While there has been a lot or range comments on PSI for my new 225/75R 15 G/Y Endurance Tires so I decided to call Can Am Airstream of Ontario and gave them my stats on the 27FB loaded for camping , with a scaled weight of 6200 lbs on the axles ready to camp.



He stated that" I would be well in range @ 55lbs"and no higher than 60lbs.
He also stated that they would not send me out on the road any higher than that. .


I guess you guys that have posted those numbers are correct.....>>>or unless you disagree with the Tire MFG and the dealership that sells and services a lot Airstream Trailers.
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Old 03-25-2019, 06:31 PM   #102
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You are free...

...as long as you don't exceed the sidewall max pressure set by the tire manufacturer you are correct...the said table states the 'load limits' for various pressures.
You are free to set any pressure within those parameters, and be confident the Forum TP Police won't have any grounds to pinch your knickers.

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Old 03-25-2019, 09:05 PM   #103
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Well, the TP police may get their “knickers in a knot” during the spirited discussion...
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Old 03-25-2019, 09:52 PM   #104
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Quote:
Originally Posted by LAWBC View Post
While there has been a lot or range comments on PSI for my new 225/75R 15 G/Y Endurance Tires so I decided to call Can Am Airstream of Ontario and gave them my stats on the 27FB loaded for camping , with a scaled weight of 6200 lbs on the axles ready to camp.

You may have a scaled weight of 6200 pounds. The assumption is each tire/wheel is loaded equally or 6200 divided by the # of tires.

Frequently RVs and trailers in particular are loaded unequally. In that event a user could inflate all tires to the average weight. And at the minimum recommended pressure, some or one tire would be over loaded and the rest would have a good margin. That one or two tires would get stressed over the long haul and may have an early failure. Or at least be vulnerable to an adverse condition that otherwise could be handled and survive.

Most TVs or passenger vehicles do not have that issue.


>>>>>>>>>>>>>>>Action
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Old 03-25-2019, 11:11 PM   #105
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Just kidding of course but, NO ONE SHOULD BE TRAVELING 87 MPH TOWING AN AIRSTREAM. Check with AAA, DOT etc. Typically if speed post says 65 mph, its 55 mph for towed vehicles. Remember back in the day when signs were 60 cars/55 trucks. Rules still apply legally. Some speeds out west 75 & 80mph , that's for passenger vehicles on a clear day.

Interesting. I had an original brochure with my 1975. The copy was clearly written before 1973, and suggested that 70 mph was a normal towing speed. Airstream tires were 7.00x15 light truck tires back in those days.

The 55 limits are unreasonably restrictive on controlled access divided highways, where design speed is typically 80 mph. I tow at 60-65 mainly for fuel economy, but I’m fine with 70-75 with a good setup and proper tires. (Solo, I’m comfortable with a great deal more than that.)
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Old 03-25-2019, 11:15 PM   #106
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You may have a scaled weight of 6200 pounds. The assumption is each tire/wheel is loaded equally or 6200 divided by the # of tires.



Frequently RVs and trailers in particular are loaded unequally. In that event a user could inflate all tires to the average weight. And at the minimum recommended pressure, some or one tire would be over loaded and the rest would have a good margin. That one or two tires would get stressed over the long haul and may have an early failure. Or at least be vulnerable to an adverse condition that otherwise could be handled and survive.



Most TVs or passenger vehicles do not have that issue.





>>>>>>>>>>>>>>>Action


At 55 psi, those tires have a capacity of 2270lbs each, for a total of 9080lbs, if my mental arithmetic is accurate tonight. That will be fine even with the trailer loaded to its full GVWR.
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Old 03-26-2019, 06:56 AM   #107
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At 55 psi, those tires have a capacity of 2270lbs each, for a total of 9080lbs, if my mental arithmetic is accurate tonight. That will be fine even with the trailer loaded to its full GVWR.
Don't be so sure of that.

The tires could be unevenly loaded - I've been using 15%, but 10% might be closer to the worst case.

The tires shouldn't be loaded to more than 85% of their rated load.

The load tables for ST tires are set up for 65 mph, and if you want to tow at 75 mph, you need to reduce the load by 10%.

And if you want to tow up to 85%, the loads have to be reduced a further 10%.

Doing the math, this worst case results in tire load carrying capacity of 5674# - compared to a 6200# GVW.
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Old 03-26-2019, 10:26 AM   #108
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ST tire Load & Speed

Before anyone jumps on Capri here is a shot from USTire & Rim Association standards book.


Note the adjustment for inflation and loading based on operating speed


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Old 03-26-2019, 01:05 PM   #109
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Endurance Tire pressure on 27FB Int'l

Quote:
Originally Posted by ROBERT CROSS View Post
...as long as you don't exceed the sidewall max pressure set by the tire manufacturer you are correct...the said table states the 'load limits' for various pressures.
You are free to set any pressure within those parameters, and be confident the Forum TP Police won't have any grounds to pinch your knickers.

Bob


����
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Originally Posted by rmkrum View Post
Well, the TP police may get their “knickers in a knot” during the spirited discussion...

as you say and its coming.

Decided to set ,, ,,,,,,,,,,,,55.0 PSI
and that number gives me + 30% margin .

I have considered, what if I get a flat at highway speed of 65 mph. Will the other tires be able to compensate, considering not all tires carry the same load ?

The answer is if it happens the margin is there.
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Old 03-26-2019, 01:06 PM   #110
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I would assume the inflation numbers regarding speeds greater than 65 MPH on the bottom of that chart only pertain to ST tire design.

For LT tire designs would there be a pressure or load adjustment for speeds greater than 65 MPH?

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Old 03-26-2019, 02:58 PM   #111
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Quote:
Originally Posted by Tireman9 View Post
Before anyone jumps on Capri here is a shot from USTire & Rim Association standards book.


Note the adjustment for inflation and loading based on operating speed


And I note, the date on this chart is 2010....think the technology and compounds might have improved a little...just a little by now?? I still am putting my faith in the Mfg. recommended chart, in my case GY for the Endurance tires I am running.

Lots of experts and experience here for sure, so go with what you feel most comfortable with. I can only repeat as others have noted, the Endurance tires when at or near "Max" pressure of 70lbs on my AS gave me popped rivets, broken hinges via stripped screws on doors, and a generally rough or stiff ride. Don't have that issue when running at the PSI of between 45-55PSI for my 28's weight.
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Old 03-27-2019, 06:18 AM   #112
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And I note, the date on this chart is 2010....think the technology and compounds might have improved a little...just a little by now?? ….....
Actually, it's a law of physics kind of thing.

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…… I still am putting my faith in the Mfg. recommended chart, in my case GY for the Endurance tires I am running, ,,,,,
And my comments weren't specific to a certain make and model of tire. In your case, the speed rating overrules the 65 mph speed restriction (and the adjustments for higher speeds) - however, that doesn't apply to tires that don't have speed ratings (or more precisely, those who also have speed ratings in the 65 mph range.)

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I would assume the inflation numbers regarding speeds greater than 65 MPH on the bottom of that chart only pertain to ST tire design.

For LT tire designs would there be a pressure or load adjustment for speeds greater than 65 MPH?

>>>>>>>>>>>>>>>>Action
Sort of.

Ya see, LT tire load charts are also predicated on a 65 mph speed restriction - HOWEVER - if an LT tire has a speed rating that speed rating becomes the speed limitation - AND - since pretty much all LT tires have them, the 65 mph speed restriction doesn't apply.

The same is true of ST tires. If an ST tire has a speed rating, the 65 mph speed restriction is replaced by the speed rating - and as gypsydad pointed out above, he is using Goodyear Endurance ST tires which have an N speed rating (87 mph).
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Old 03-27-2019, 12:06 PM   #113
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Barry and I are the only two actual tire engineers on this forum as far as I know.

Neither of us work for GY but we both worked for many years at two other major tire companies. We both understand the physics of tire performance.
The load tables are published every year.



I do not recall ever seeing any change in load capacity for a given size once it is in the published book. So tha answer is... No, tire load capacities are basically fixed based on physical size ( air volume) and service type ( P or LT or ST) and do not change over the years.



If you think GY has some "magic" tire construction that suddenly allows both an inflation reduction and a load capacity increase don't you wonder why they don't use that "magic" in their first line P and LT type tire?
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Old 03-27-2019, 09:14 PM   #114
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Just When i thought i understood this stuff i think i read the link in my earlier post (#33) at least 5 times before it clicked...apparently i'm not hearing well.

Never understood why the chart indicated 87 on a 65 rated ST ( GYE 225/75/15e)

First off, to be clear i have no plans or desire to tow at 87mph...breaking the 65 threshold only in brief spurts when passing. The exception and not the rule. My sweet spot is about 62-63.

My scale weight per tire, using the higher ds/cs value x2 and then adding the required 15% margin puts me at about 70-72psi. I run at 75. They retain pressure incredibly well and very. few rivets popped.

Just so i understand this, if i wanted to tow at 87, i don't need to add additional pressure to get me from 65 to 87.....because the N rating on the gye E tire already gets me there. Is that correct? I was thinking my math above got me to 65.

Thanks

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[Sort of.

Ya see, LT tire load charts are also predicated on a 65 mph speed restriction - HOWEVER - if an LT tire has a speed rating that speed rating becomes the speed limitation - AND - since pretty much all LT tires have them, the 65 mph speed restriction doesn't apply.

The same is true of ST tires. If an ST tire has a speed rating, the 65 mph speed restriction is replaced by the speed rating - and as gypsydad pointed out above, he is using Goodyear Endurance ST tires which have an N speed rating (87 mph).[/QUOTE]]
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Old 03-28-2019, 06:24 AM   #115
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...… Just so i understand this, if i wanted to tow at 87, i don't need to add additional pressure to get me from 65 to 87.....because the N rating on the gye E tire already gets me there. Is that correct? I was thinking my math above got me to 65. ….
Yes, that is right.

But I think the best way to look at this is that while 87 mph is the upper limit for an N speed rated tire, doing so eats up all the reserve - making it more likely that a failure will occur.

Ya' see, this is all about REDUCING the risk of failure. There isn't a clear, bright line between failure and non-failure. The line is very fuzzy and anything there are many things that can be done to improve the odds
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Old 03-28-2019, 09:21 AM   #116
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Perfect, thanks CR. Yours and TM9's feedback is very much appreciated.

I have no interest in pushing the limits but prefer to minimize all rizk.

Bkb

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Originally Posted by CapriRacer View Post
Yes, that is right.

But I think the best way to look at this is that while 87 mph is the upper limit for an N speed rated tire, doing so eats up all the reserve - making it more likely that a failure will occur.

Ya' see, this is all about REDUCING the risk of failure. There isn't a clear, bright line between failure and non-failure. The line is very fuzzy and anything there are many things that can be done to improve the odds
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Old 03-28-2019, 10:31 AM   #117
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The comfortable reserve the ST tires even , make me wonder if on airstream tires last as long as LT tires , so 6 years or more.
And not the sometimes 3 to 4 years ,as they five for ST.
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Old 03-28-2019, 10:40 AM   #118
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Point of clarification.

The Tire & Rim Association Load formula used by the industry for ST type tires is based on a 65 mph max operating speed. Neither P or LT tires have stated max speed as part of the formula section of the TRA "Engineer Design Information" aka EDI book.
P-type have the stated 1.10 "De-Rating" of load capacity when used on a trailer or P/U.
LT tires have no de-rating when placed on trailer nor do they get an "up-rating if placed on passenger car so we could consider LT kind of the standard for load capacity.


If you look at similar physical sized tires and include the P Derating you will see the de-rated P and LT tires give similar results for load capacity.

BUT the load capacity of the ST type is significantly higher. Why would that be if there were not some other controlling factor i.e. the 65 mph speed limit? Some people would have us believe that ST tires all had some magic rubber added to them in 2017 when speed ratings higher than 65 were added. The reality is that the speed rating was added to avoid import tariffs.

Maybe you think that all the different tire companies used this "magic" rubber to give them an overnight increase in speed capability.
Why isn't there a single tire company anywhere in the world using this "pixie-dust" in their LT or heavy truck tires to give them an extra 10% to 25% more load capacity?


I have examined a section of a GY Endurance and it clearly has "better" construction than some non-speed rated tires. Only time will tell if this new construction results in a better life and if so how much better.



What I have not seen is anyone changing their advice on tire life in RV usage. What trailer company now says up to 10 years life or even claims over 5-year life?
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Old 03-28-2019, 02:28 PM   #119
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Tireman9 wrote
I have examined a section of a GY Endurance and it clearly has "better" construction than some non-speed rated tires. Only time will tell if this new construction results in a better life and if so how much better.
-load

Have you compared the sectrion of Endurance E-load with ST D-load, then the better construction is yust to hold more pressure in.
Have you compared them with same sise E-load LT tire, then probably pretty similar construction and the higher maxload then that LT E-load can only be because of the still 65mph for wich the Endurance is calculated , in compare the LT for 99mph mostly.


the aditional service descriptions that are given in Europa on most Trucktires, ( fi 156K and additional 154L) is also only because of the speed its calculated for and not the "magical dust" that only works up to 110kmph belonging to K speedrating.
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Old 03-28-2019, 03:36 PM   #120
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R we confusing each other yet?? (or just having fun!) Knowing the limits by the Mfg. is one thing; I certainly would not be pushing the limits at 87mph! But, as I mentioned about materials used, sidewall and tread construction, and Mfg. load/pressure limits, is good to know and understand. We all know that an ST tire has stiffer sidewalls then an LT tire, and clearly more than a P rated tire, right? Stands to reason the lateral load is much greater on a TT (thus the stiffer sidewall construction), then on a pickup or passenger vehicle. It's great to get the experts agreeing on following the Mfg. chart on the Endurance...thanks for sharing your experience!
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