Check my math on tire inflation, please

[Rocketsled]

We had a lot of evidence that something 'wasn't right' on the trailer.

The old tires wore out on the back axle on the inside edge, We'd find the mattress on the top bed in the garage would flop down after a day's travel, there was evidence of the garage windows wrinkling the wallpaper, presumably due to movement.

So...New Powerking Tow max tires were installed in Gunnison Colorado, as they were the only tires in town and we weren't going to make it to Denver on the old tires.

Then $3500 worth of suspension upgrades to restore the rear axle alignment, springs, and Moryde CRE3000 suspension.

When the tires were installed, I asked them what they recommended for tire pressure and he said 'we just pump em up to 90psi and leave them.'

Which comes to my question:

With the trailer loaded for normal travel plus a full tank of fresh water, the weight on each tire is about 2500 lbs...looking at load/inflation information for the tires (here, there's a BIG discrepancy between what it thinks I need, vs what 90psi provides.

50psi would apparently handle 2600 lbs, and 90psi would handle more than 3500 lbs (the chart doesn't even list numbers for 90psi, max numbers in other documentation show 3860 @ 100)

50 psi seems...kinda crazy low. The last set of tires were run at 80psi.

Does it seem safe to run, say, 60 psi (2870 lbs) to cut down on the screws backing out due to vibration and reduce the sawdust we have to sweep up at the end of each drive? I'm a bit concerned we're going to use the trailer up prematurely by shaking it apart.

[JRTJH]

First, there is NO 90PSI pressure recommendation for any ST tire manufactured by TowMax. Since you didn't include the size of your tires, I'd make a guess that they are either 225 75R15 LRE or 235 80R16 LRE both of which carry a "recommended tire pressure of 80 PSI.

That said, most recommendations for tire pressure maintenance on ST tires recommends the maximum sidewall pressure as "molded in the sidewall".

Also, the recommended tire size and tire pressure is provided by Keystone and is printed on the weight certification sticker located on your trailer. It's located on the roadside front corner of your RV.

If you think about it, it's air pressure that gives you the load carrying capability. Airing down tires reduces the tire's ability to carry a load. On RV's you want the maximum capacity to not only provide the maximum load carrying but also to prevent tire damage from sidewall flexing which produces heat, the $1 enemy of tires. Also, keeping your tires at the maximum sidewall pressure will help prevent damage during "tight maneuvering typically done in campgrounds, fuel stations and most "backing operations"...

If you want more discussion on "YOUR" specific situation, I'd strongly recommend that you provide the tire size, load range and the specific reasons you had to replace them.

[Rocketsled]

They’re 235/80R16

https://www.towmaxtires.com/tire/details/towmax-str-ii

There’s documentation from the manufacturer for running them up to 100 psi

After posting, I was looking through the documentation for the suspension and it had a curious footnote under troubleshooting for a rough ride:

* According to tire manufacturer specifications, proper tire pressure means inflating tires according to individual wheel weights (as long as a wheel is not overloaded), not necessarily inflating to the maximum pressure as specified on the tire.

Which takes me back to the original question: running at max pressure (and admittedly messed up suspension) was shaking the trailer apart.

[JRTJH]

The 235 85R16 tire that you see with a recommended pressure of 100 PSI is a 12 ply Load Range F tire, not a 10 ply Load Range E tire. You can't (well you shouldn't) air a load range E (10 ply) tire above 80 PSI. As for weighing individual wheel positions to obtain "minute (small) weight differences, is really way more complicated than most people are willing to go or "can even go".

When you consider that every manufacturer recommends that both ends of an axle MUST carry the same tire size and pressure, even weighing "individual wheels means you're going to be "airing up to the heaviest side on that axle. Then you get into the issue with a tandem axle of "do you run the front axle pressures different from the rear axle pressures" ??? Most people would recommend that you run the same pressure on both axles. So, you're "airing up each side to the heaviest and airing up each axle so they all carry the same load (across the equalizers)....

Now that really gets us back to what's printed on the load chart/cheel chart/weight chart that's attached to the front roadside corner of your trailer... What does it recommend for tire size and pressure ???

[CWtheMan]

You need to verify the maximum load capacity for your tires. It’s displayed on the tire sidewall. The maximum permissible inflation pressure for the load capacity will also be displayed there. There is a possibility that TowMax may have increased the load capacity for those tires to 3860# @ 100 PSI. That tire size – ST235/80R16 LRF at 95 PSI - will not qualify for service on 7000# axles. 3780# is needed to comply with a RVIA recommendation for 10% reserve load capacity. However that tire with a load index number of 127 @ 100 PSI will. (I’m not saying you have 7000# axles. That’s just information to support a hypothetical reason for TowMax to make those tires a LRF+).

There is nothing in the FMVSS standards that recommends inflating your trailer tires to the load carried. The correct inflation pressures are displayed on the vehicle certification label, vehicle owner’s manual and on the tire and load placard.

The procedures for replacement tires are standardized throughout the industry. The basic standards say that replacement tires MUST provide a load capacity equal to or greater than what the OE tires provided - via recommended cold inflation pressures. Inflation pressures above what has been recommended and all the way to sidewall max are always optional.

Inflating trailer tires to the load carried may cause them to be operated without any, MUCH NEEDED, load capacity reserves.

[Rocketsled]

The sticker on the trailer lists ST235/80R16E tires at 80 psi (to close the loop on a question above), the 90 psi recommendation was from the tire shop that installed the tires, I can see that to be probably ill advised. Nor was I suggesting running 100 psi, only that it had been mentioned in the documentation from the tire vendor.

I can also see that, despite weighting the trailer and completely replacing and renewing the suspension (one new 7000 axle, and the other showing perfect alignment, replacement of springs with an additional leaf (which was okayed by Dexter), wet shackle kit and the CRE3000 equalizers, and finding a load/pressure chart for the tires that are actually on the trailer...

That I need to keep everything at the capability to support 14,000 lbs, and just accept the trailer shaking itself apart as something I can't do anything about. (and the GVWR of the trailer being 13,000 lbs)

According to https://fifthwheelst.com/documents/T...lation2014.pdf 50 psi would be adequate to carry the actual weight (yes, I know things vary based on n altitude, roads, individual loading, and I am not advocating running that close to the edge). 65 psi would have a comfortable factor of safety over actual measured loads...but 80 psi is it.

[CedarCreekWoody]

Run no less than the amount on the trailer sticker and no more than on than on the tire sidewall. Experiment in between the two if you wish.

[jasin1]

So i have a question... should you ever rotate fifth wheel tires or have them rebalanced ? I’m thinking if there are different actual weights on different tires depending on kitchen layout or other factors...yes or no?

[ChuckS]

If I read the initial post right (Toy Hauler) and you got E rated TK tires.. that RV needs G rated tires if you want any sort of safety margin.. ANd what are the wheels stamped at for MAX PSI on backside...

Id be running a Sailun S637 series tire or Hercules 901 series tire on a toy hauler and it would be G rated an nothing less

And I could care less what the stupid sticker says on the side of the RV

[Rocketsled]

So. Called MorRyde this morning and they confirmed some of my thoughts:

Tires should be inflated to the weight specified in the inflation chart...he directed me to the Goodyear chart (https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf ) which, curiously, is IDENTICAL to the Towmax chart (https://fifthwheelst.com/documents/T...lation2014.pdf).

The sidewall of these tires provides part of the suspension compliance...If you run them up to max pressure, all things being equal and in-spec and not overloaded...you're giving up some of the designed compliance in the suspension and can run the risk of over-inflation tire wear as you don't have the weight to counteract the pressure being run in the tires.

He was naturally and reasonably reluctant to recommend a pressure without weights at each tire (as mentioned by JRTJH above), but I don't see how running at 70psi rather than 80 would cause irreparable harm and the 90 recommended by the tire shop is WAY too much. I'm toying with going back to CAT scales and placing each axle on seperate pads and calling it good.

70 psi gives 12560 lbs of carrying capacity, which is 2560 higher than the trailer weighs with a full tank. If I ever get around to throwing the motorcycle in back (850 lbs), I'll run with the fresh tank empty.

Try slowing down over those rough roads. I'd guess shaning 10 mph off your speed would make a difference.

We're firmly in the 'max speed 65' club. I'm thinking the lion's share of the damage was the back axle and leafspring damage...that's been corrected, and the trailer rides much better in the little bit I drove it prior to putting it away for the winter, I'm just handling the long-tail parts of the equation.

[Rocketsled]

Originally Posted by ChuckS

If I read the initial post right (Toy Hauler) and you got E rated TK tires.. that RV needs G rated tires if you want any sort of safety margin.. ANd what are the wheels stamped at for MAX PSI on backside...

Id be running a Sailun S637 series tire or Hercules 901 series tire on a toy hauler and it would be G rated an nothing less

And I could care less what the stupid sticker says on the side of the RV

We paid High-country prices for new tires in Gunnison...they're not the best tires, but I'm going to get a season or three out of them before I put something different on (I was shopping Sailun and Goodyear before the trailer told me I was changing the tires or I wasn't getting home.

Between the suspension repair/upgrades and the tires, I'm $4k into it...I'd like to get some use out of that before throwing away new 'less than the best' tires.

[sourdough]

Originally Posted by Rocketsled

We paid High-country prices for new tires in Gunnison...they're not the best tires, but I'm going to get a season or three out of them before I put something different on (I was shopping Sailun and Goodyear before the trailer told me I was changing the tires or I wasn't getting home.

Between the suspension repair/upgrades and the tires, I'm $4k into it...I'd like to get some use out of that before throwing away new 'less than the best' tires.

Don't know how long you've been towing an RV but if you're new better get used to the "throwing away" new/nearly new stuff for any number of reasons. If you've been doing it a long time you must know it is an expensive "hobby". I have shelves full of new/nearly new unused/barely used anything and everything in the barn except the new Ranier tires that came on this trailer - I gave them away as soon as I picked up the trailer - I didn't get a season, or three, or a mile from them....I just didn't want them on my trailer. I leave all the other stuff on the shelves so I can go in and look at them when I'm in the barn, smile, shake my head and.....place that new "whatever didn't work" on a shelf beside the others.

If you have the Morryde suspension you have the best there is IMO. I had it on my last trailer; even upgraded to a higher load range at max sidewall pressure and had zero problems inside the trailer - nothing of any kind ever moved - after I found the culprit. I could watch the trailer in the mirrors on all kinds of road conditions and it always looked like it was floating on a cloud. I highly doubt your tires are causing your problems. My problem that caused doors to open? A truck not up to carrying the load of the trailer. Upgraded to a 3/4 HD truck and it all stopped completely. The 1/2 ton was bouncing, jouncing and jolting the trailer - the HD stopped that.

So if it's not tires (I highly doubt) or suspension then it must be one of the other things mentioned; driving habits, road conditions or truck. What truck are you towing this with?

[CWtheMan]

Originally Posted by ChuckS

And I could care less what the stupid sticker says on the side of the RV

It's not a "stupid sticker". It's a federal vehicle certification label. The statement below insures the vehicle has passed all safety standards at the time of first sale. There is more detailed information in the reference below the quoted statement.

“This vehicle conforms to all applicable Federal motor vehicle safety standards in effect on the date of manufacture shown above.” The expression “U.S.” or “U.S.A.” may be inserted before the word “Federal”.

https://www.law.cornell.edu/cfr/text/49/567.4

[flybouy]

"That I need to keep everything at the capability to support 14,000 lbs, and just accept the trailer shaking itself apart as something I can't do anything about. "

I would have to disagree with this statement. Try slowing down over those rough roads. I'd guess shaning 10 mph off your speed would make a difference. Folks with rear kitchens are always fighting the issue of securing things as the rear of any trailer gets the most bounce. But "shaking itself apart" means your driving too fast for the road conditions if everything else is correct (hitch, trailer and truck suspension, etc.)

[Bill-2020]

I was told once by an individual that travel trailers and the such are essentially traveling earthquakes. Makes sense to me. One day I’ll mount a small video camera inside and and record a short trip just for yucks to see what it looks like inside. Your addition of the CRE equalizers (or any dampened equalizer) will help. I noticed a substantial change in ride on our small Passport with the CRE3000 equalizers after I installed them. Yes, you can tell from the TV when new/better suspension parts are installed.

[travelin texans]

Personally I'd run them at whatever the sidewall recommends or what the rv manufacturer recommends or somewhere in between, but not less than the lowest of the 2. If you've upgraded to a higher load range go with what the sidewall states if the wheels will allow it.
You've got the suspension upgrades to almost the best on the market, IS is #1, so the ride inside shouldn't be an issue or as the other Danny stated you've got other issues besides tires.
I've had numerous RVs with the tires inflated to the cold sidewall pressures & never had unusual tire wear due to overinflation, now under inflation, alignment or so called "China bombs" have been issues.

[sourdough]

Originally Posted by travelin texans

Personally I'd run them at whatever the sidewall recommends or what the rv manufacturer recommends or somewhere in between, but not less than the lowest of the 2. If you've upgraded to a higher load range go with what the sidewall states if the wheels will allow it.
You've got the suspension upgrades to almost the best on the market, IS is #1, so the ride inside shouldn't be an issue or as the other Danny stated you've got other issues besides tires.
I've had numerous RVs with the tires inflated to the cold sidewall pressures & never had unusual tire wear due to overinflation, now under inflation, alignment or so called "China bombs" have been issues.

The above would be right. I was just referencing the current situation with this trailer and the situation he is facing and what he has.

[GHen]

Aside from the tire over/under pressure conversation, here are a couple other possible issues. The symptom was vibration, what was the cause was not determined.

The Op replaced the axel, I assume the rear? Many people have had this same issue. Consider the possibility the rear axel was bend due to extreme tire twisting due to tight turn and poor quality suspension.
When turning very tight, pull forward a foot every few feet to release the possibility of damaging the new axel. My daughters rear (Dexter) was replaced under warranty, it was a mess even though the trailer was properly loaded.
With that said, these worn out tires could have been way out of balance and alignment causing the excessive vibration.
The question to the OP, has he confirmed excess vibration after the new tires, axel and suspension was installed?
Vibration can be caused by driving too fast on rough roads etc, yes, but maybe eliminating the majority of vibration caused by worn out running gear and having well balanced tires could solve some or most of the vibration problem.

Then air pressure may not be the big deal.

I run at max pressure on the tires which is also the recommended tire size from the manufacturer. When you run tires that don’t meet specifications by the rv manufacturer, then everything becomes confusing. But that’s a load issue not a vibration issue.

[Ken / Claudia]

OP has a interesting way to do math. I made that part of RVing really easy, I read the manual about ST tire inflation and did not think I know more or better and followed that guide line. I read the tire sidewall and sticker on the trailer that had the same guideline. That part about RVing is easy.

Only way I have found to end the RV from experiencing road vibration after owning about 7 RVs in 40 years is to not pull it any where. They all do every single one. One could spend endless money on better axles, springs, shocks, hitches, tires and inflation. What about a proper tow vehicle and it's ability's to add to or not, more or less road vibration into the trailer. What about how, what and where you load stuff in the RV. That could play into this whole picture.
In the end a RV is never going to ride, handle like any passenger car or pickup. It's the roads, conditions and the way one drives that will have the most effect on vibration. If you have all the stuff mentioned working as it was suppose to do. Spending 4 grand on upgrades? Likely was a good thing, trying to under inflate tires to get a better ride is silly.

[JRTJH]

Before reducing pressure in tires (which also reduces load carrying capacity) and increasing the potential for catastrophic tire failure causing thousands of dollars of trailer damage, I'd ask:

Have you installed (or considered installing) shock absorber kits on your axles?

If you've added $4000 in upgrades to the axles and haven't considered $375 to install shocks on both axles, then I'd think before "screwing up the tires by playing with tire pressure" I'd entertain spending the money to install shocks...

https://www.etrailer.com/Trailer-Lea...BoC9-wQAvD_BwE