Endurance Tire pressure on 27FB Int'l

[SteveSueMac]

Originally Posted by gypsydad

Thanks for that. No disrespect intended for Capri. My interpretation from my discussions with GY was the PSI numbers posted for given load were minimum; not maximum. Sorry if I confused anyone. Not sure where the "+15%" advice is listed anywhere by the Mfg I could find? But, likely not a big deal.

My point is, each tire Mfg. has a "recommended" chart for their tires; why not use that if you know your trailer weight for best performance?? My experience was Discount Tire who installed my replacment GYE's last summer, put in 70PSI; might be ok if my AS weighed in at 10,488lbs! But it was to much air for my 28', which weighs 7,580lbs. When the tires were too stiff, it caused popped rivets, hinge issues, and other issues inside- like cloths closet above foot of my twin bed with TV coming loose, closet door coming off in hall, and also shower door coming loose and hanging down; all this after I put on the new tires...in just a few trips!

I adjusted tire pressure down to between 45-50PSI per the chart after discussions with GY and also discussions on the Forum last year and have had no issues since after towing from MT to TX and several trips since.
As always, your mileage may vary, as may your opinion.

Got it. I saw no disrespect to anyone in your note at all FWIW....

Thanks for helping me understand how you’re seeing the load chart. You see the cells in the table as minimums. We’re on the same page.

The 15% doesn’t appear to be the manufacturer’s recommendation - just something we see in the forums by the handful of tire engineers who participate here; recommended for the reasons I stated earlier. That answers the question of why not use the manufacturer’s recommendations - especially if you don’t have individual weights for each tire or account for adding more pots and pans (or rocks, like Lucille Ball....).

[Baby Zeppelin]

This shouldn't be rocket science. At 80 psi we had popped rivets and broken cabinet latches.

Now I use the following formula calculated with my tongue in my cheek:
Start with that 80 psi, multiply by driver's age converted to %, then multiply by a safety factor of 120%.

For my trailer that comes to about 65 psi. I start with that, it goes up about 7 psi as the tires warm up. So far so good. May have to rethink this if I'm still towing into my 80's.

[urnmor]

I run mine between 65 and 70 and it seems to run fine

[SteveSueMac]

Originally Posted by Baby Zeppelin

...snip...

Start with that 80 psi, multiply by driver's age converted to %, then multiply by a safety factor of 120%.

Perfect! [emoji3]

[CapriRacer]

Allow me to fill in some gaps.

When talking to tire manufacturers, you have to be very careful what you ask and how you ask it. In the case of cars and SUV's, those vehicle manufacturers have done a good job of sizing their tires (or at least they have since 2008.) The vehicle tire placards for cars and SUV's (which specifies both the tire size and inflation pressure) is at least 15% more than the designed max tire load. So tire manufacturers are very confident that following the vehicle tire placard is what the average consumer should do.

But when it comes to trailers, the situation is much more involved. In the past, some trailer manufacturers specified tires that were - at times - overloaded. I don't know what the situation with Airstreams was (or is), so I am taking a cautious approach. That's why weighing the trailer is so important. The goal is to find out what is the most load put on a tire - and then inflate it to get MORE load carrying capacity.

The way this ought to work is that trailer's tire placard OUGHT to have a reliable value on it - but given the past, we can't be sure of that. So I am doing what the car and SUV manufacturers do - selecting a tire size/pressure that is 15% MORE than the worst load.

And lastly: Look very carefully at the tire load tables. Do any of them say RECOMMENDED? They do not. Somewhere there will be a note about minimum or maximum. It's just good engineering to specify more than the minimum.

[jadatis]

The reserve you have to take, depends on the expectation of weight in use.
And that variates by vehicle-kind, but also by the region.
To give an example .
In my country the Netherlands, for motorhomes, max allowed GVWR is 3500kg/7700 lbs, for the driverlicence most only have.
For that reason ther are many motorhomes sold, with empty weight of 3000kg/6600 lbs.
You would think a comfortable 500kg1100lbs payload. But bij the way a motorhome is build, much is stored close to rear axle or behind it.
Common gawr's are F 1850kg/3070lbs and R 2000kg/ 4400lbs.
So many motorhomes here are overloaded on rear axle. I even think that there are a few who are empty already overloade on rear or that little reserve, that in practice it must be overloaded .

So for tirepressure advice, I calculate for rear gawr+18% . If then realy gawr on rear, the tires use 85% of the loadcapacity that belongs to the pressure. This 85% I baptised loadpercentage.
Once determined, but discussable, is that this gives max reserve with still acceptable comfort and gripp.
If now axleweights are given, only 10% reserve ,also rear, to cover unequall load R/L. Wich always is the case. Then if equally devided, loadpercetage ( further L%) 91 % , so still a weightdifference possible before one side bumps.

In my traeltrailer spreadsheet I add 11%to assumed axleweight to make L% 90% ,
And allow on tire L% 80% because no persons in it, only so the scews( rivets read in this topic) wont remble loose. For instance axleweight 1800 , and one side 800 and other side 1000 , pressure calculated for 1000, so heavy side L%100% , light side L% 80%, heavy still no overheating and light side still no bumping. This would mean a weightdivision of 44.5%/55,5%.
Les weightdifference always covered.

The TT or motorhome maker have other standards, mostly calculated for GAWR without reserve. Or nowadays always referencepressure of tire ( if you read my former post you know that this is the 65 or 80 psi most)

That is why me and also Tireman9 and Capry Racer give other advice then the tiremakers often give.
Most people have a religius trust in the information of tire and vehicle makers.
But history made that laws of nature dont always stroke with laws and standards of the manufacturers. And mother nature dont give penalty's , she yust makes your tires blow, if pressure to natures law to low for speed and weight.

[SteveSueMac]

Just had a set of GYEs (ST225-85R15 E-rated 80 PSI max - made in July 2018) installed today on my 27FB Flying Cloud. Had Michelins on it for the last 5 years. Decided to go back to an ST given that the GYEs seem to be doing well. The 15” Michelins (passenger classification) carried 1984#/tire at 50 PSI (de-rated 10% for the application). I have the GYEs at 60 PSI - 2300#/tire. On the scales, they see 6000# or an average of 1500# each. More than 50% spare capacity at that pressure. Have to go back to the scales to start this year off - some differences with the full topper and additional gear to be carried while clearing out some over-accumulation in the trailer. Will see how it goes and possibly drop them back to 55 PSI if needed.

The 4 on the axles have the new banded TPMS internal sensors to pair with my TST 507 - the spare (which had never been used and was replaced with a fresh GYE as well) will have an external sensor put on it to also pair with the monitor.

I’ve used external and internal sensors. Internals (prior and current version) indicate about 10% rise in pressure and temps about 30* above ambient. External sensors measure differently. They usually showed about 1-3# rise in PSI and about 5-10* above ambient.

BTW - used my TireMinder ramp to pull up on it one at a time rather than jack it up. The tire technician didn’t mind (and I tipped him very well...).

The GYEs look and feel MUCH different than the GYMs. They seem (to my admittedly untrained eyes) to be more substantial and better built. We’ll see!

[SteveSueMac]

Dang - 225-75 (not 85)....too late to edit....

[jadatis]

Answer to above.
If P-tire standard load , the old caries 19?? Lbs AT 36 or 35 ps, the 50 psi is the max pressure the tiremaker allows. Search back my post here with picture of speedcodes.
If XL AT 42 psi or 41, so still not 50.
Give gvwr or real total weight, and tire specifications, and I will trow it in my calculator.
Give them of old and new tires, so we can compare.

[ROBERT CROSS]

Where is the question?

Bob
🇺🇸

[SteveSueMac]

Originally Posted by jadatis

Answer to above.

If P-tire standard load , the old caries 19?? Lbs AT 36 or 35 ps, the 50 psi is the max pressure the tiremaker allows. Search back my post here with picture of speedcodes.

If XL AT 42 psi or 41, so still not 50.

Give gvwr or real total weight, and tire specifications, and I will trow it in my calculator.

Give them of old and new tires, so we can compare.

I wasn’t asking a question. [emoji3]

I had Michelin P225-75R15 LTX MS/2 tires. If using a P (passenger) tire on a trailer, you have to de-rate the capacity dividing by 1.1 which resulted in 1984# @50 PSI. My CAT scale tickets show the trailer axles see 6000# fully loaded for camping (980# on the tongue). That’s 1500# average per tire on the 2 axles. Using 50 PSI in those tires gave me 30% extra load capacity.

I could probably do the same with the new GYEs - I’m starting at 60 PSI and may adjust if needed.

[LAWBC]

Originally Posted by ROBERT CROSS

What size tire?

Bob
🇺🇸

My tire size .

225-75 -15 on the same OEM rims .

[Tireman9]

RE having at least +15% Reserve Load. Most cars & trucks run 24 to 30% reserve load
Trailers only recently run 10% from the RV company (Tire capacity over the GAWR)


You can't assume your actual tire loads. At a minimum you need individual axle scale wights when the RV is loaded with as much "stuff" as you ever expect to carry.


RE Speed rating. This is just a relative rating of heat resistance. ST tire loads are calculated using formulas based on a max operating speed of 65 mph.

[ROBERT CROSS]

Originally Posted by LAWBC

My tire size .

225-75 -15 on the same OEM rims .

Same as the original GYM's on my Classic.

All I can say I ran two sets at 68psi for 11 Seasons without a failure. Other folks say they are junk...other than a self inflicted curb rash failure I had no problems.

Bob
🇺🇸

[sctinman44]

Originally Posted by gypsydad

Thanks for the clarification; I had poor luck on my Casita with Maxxis several years ago..1 blow out and the other bubble which I caught while on a trip. That was 18 years ago, however.

To answer your question about towing speed, only people driving 87 with an AS are those wanting to pass someone who can only go 65 with their Maxxis! (just kidding of course!)

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. Not on a rainy day, or cloudy day, or snowy day etc. Check DOT--FMCSA regulations, most of these apply to private and personal also. Per: Retired OTR ODFL many millions mile SAFE DRIVER AWARDS. No pun intended. Just kidding. Have a safe trip. God Bless America. 🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸🇺🇸

[rmkrum]

We had a completely unprovoked tread separation on a GYM that was in good condition, not over age, and fully inflated to sidewalk max as required by the trailer placard. It threw the tread partially on a clean, dry road doing 55 MPH.

This incident did over $3,000 worth of (fortunately) insured damage to the roadside rear wheel well. No more GYMs from that point forward for us.
And no sustained speeds over 65 with the current ST replacement tires. No issues, either. I’d have to go look at them to get the actual brand name. They were what was available after limping to the nearest tire store in Northern California a few years ago.

These still look to be in decent shape, lots of tread, but have aged out now. The debate and decision on which way to go from here continues apace. Needs new shoes before our big trip later this summer...

But yeah, accidentally got the rig up over 85 going across Texas one time. Was towing super smooth, then after a minute or two noticed I was running way too hot. Backed off to 65 and put it on cruise the rest of the day. Airstream plus a ProPride is bliss and smooth towing on the road...[emoji39]

[SteveSueMac]

(Random high jack)

Re: 80+MPH towing an Airstream - wait ‘til you see what happens when you hit 88!!!

(Sorry - someone had to do it - we return you to the topic at hand)

[rmkrum]

Hit it, nothing happened, settled down at a more reasonable speed. DW didn’t even wake up from her nap in the passenger seat—it was that smooth.
Of course everything was tuned and adjusted to perfection to achieve this brief excursion into madness 🥳🤬[emoji14]. Hopefully the statute of limitations has run out on that episode...

[SteveSueMac]

Well, rmkrum - you clearly don’t have a flux capacitor in your trailer! [emoji3]

[rmkrum]

Nope, last I checked, they are still on backorder...sigh.

And “Mr. Fusion” still is not on Amazon last I looked. Disappointing.

Yeah, I read a lot of Science Fiction as well. This cell phone I’m typing on is straight out of science fiction. Didn’t Tom Swift have one ? Or was it Jubal Harshaw—I don’t recall which was first mention.