Tire pressure

[CWtheMan]

Originally Posted by Festus2

CW

While Keystone is federally regulated to set the pressure on OE tires and that pressure may be found in the manual or on labels and stickers attached to the RV, once the owner removes the OE tires and replaces them with something different, then Keystone is out of the picture. I can't see anyone checking with Keystone when setting tire pressure.

When I replaced ours with Maxxis, I referred to their data and recommendations as well as the wheel manufacturer not Keystone.

The vehicle manufacturers’ recommended tire pressures are the minimum standard for all subsequent tire replacements, even plus sizing with like designs or other designs. The amount of air pressure recommend for the OE tires equates to the amount of load capacity the tire will provide with that air pressure. That load capacity is what the vehicle manufacturer has set as a minimum safety factor for the OE tires. The tire industry will not knowingly recommend replacement tires unable to provide that minimum load capacity.

That is a snip from my previous post. There are not many references on the WWW to support the industry standard for plus sizing tires. I do have one. I can post it but it requires in-depth reading and selections of the sections/portions of the pdf that fit the circumstances.

CW

On edit: This reference from Toyo may say it best.

http://www.toyotraining.com/toyo_fund_8.php

[CWtheMan]

I probably dig a little deeper into reference materials than most other tire researchers. To the best of my ability my posts about tire regulations and industry standards are factual. In other words, I don’t adlib my posts.

During the 2007 tire rules committee discussions prior to making the most recent changes to the manufacturers regulations (2007), it was determined that the federal certification label must reflect the actual tire size installed on the trailer at the time of first sale. By insuring that particular element of the regulation is consistent insures the buyer and all subsequent owners of the vehicle are aware of the vehicle manufacturers’ original tire selection.

Many first and second owners change tire sizes without regard for tire industry standards and use inferior replacements in size and load capacity. There are always tires that will meet the minimum requirements the trailer builder set with the OE tires. There are many reasons why owners will not play it safe and stay within the industry standards with replacement tires. I could describe many of them but it would just light a fire under those that have strong convictions about their own tire selections.


BA

p.s. When researching such documents as FMVSS 571.120 it will lead you to a chain of other FMVSS topics. Chief among them is vehicle certification. The reader of FMVSS regulations pertaining to RV trailer manufacturers must remember that those regulations were written for the vehicle manufacturer to abide to. Not the end user.

[Festus2]

CW -
I'm not disagreeing with your research or what the "Rules Committee", Federal Certification Labels, FMVSS 571.120 documents, industry standards and other tire "regulations" have mandated. I suspect that almost everyone on here who has switched out their OE tires, all of which are manufactured in China, for either Maxxis or some other more reputable tire, doesn't really care what Keystone has said about doing that. Keystone's tire pressure recommendations are based on the tire that they have put on the rim. Once that tire is removed and replaced with some other tire, usually an upgrade, then Keystone's recommended tire pressure is ignored. Most look at the cold pressure on the new tire and inflate it accordingly. No one looks at the inflation sticker placed there by Keystone any longer.

I would also suspect that most of us have relied on data and other information that comes from the replacement tire manufacturer - whoever that may be. If the manufacturer of the tire says 80 psi then that is what most of us follow.

Most of us are not all that interested in reading what the government "rules and regulations" are about their tires. Perhaps we should be but the reality is that it is neither practical or something that happens in the "real world".

My remarks may be adlibbed and not based on any factual data or backed up by research. I put on Maxxis because they are good tires and inflate them to the pressure that Maxxis recommends. As an "end user" I may not be compliant with all of the various departmental regulations but I do have confidence in both the tires and the pressure that is in them.

[kellydog98]

Simply put...Balanced and @80psi cold in the morning.

[CWtheMan]

Let me back-up a bit here.


“The National Highway Traffic Safety Administration (NHTSA) has a legislative mandate under Title 49 of the United States Code, Chapter 301, Motor Vehicle Safety, to issue Federal Motor Vehicle Safety Standards (FMVSS) and Regulations to which manufacturers of motor vehicle and equipment items must conform and certify compliance.”

The federal government cannot - without a national law - force individuals to conform to the safety standards they require vehicle manufacturers to conform to. Only individual state vehicle inspection laws can enforce such standards. The following statement is from the PA vehicle safety inspection. Are the tires smaller than the manufacturer’s recommended minimum size or below the manufacturer’s recommended load rating?

When backed-up to the wall I’ve always said that individual RV trailer owners are fully responsible for their selection of replacement tires. However, I’ll not back off from safety. Posting how it’s supposed to be done is a challenge.

Here is an abbreviated - by me - scenario of how to apply the vehicle manufacturers’ OE tire information when installing replacements of a different size, design or load capacity.

The first and most important steps are to ensure the trailer has enough wheel well clearance for the plus sized tire and the rims are of the correct size and capable of sustaining the new load capacity and tire pressure. Next is to insure the distance between tires on dual or triple axle trailers are acceptable. Now it’s time to look for tires. The replacement tires need to be able to provide as much load capacity (with air pressure) as the OE tires do/did. Once the desirable tires have been selected, correctly mounted, balanced and installed on the trailer a new recommended tire pressure must be determined. Using a load inflation chart for the replacement tires find the amount of tire pressure needed to equal the load capacity of the OE tires. That is your minimum acceptable tire pressure. After all that is done a notation should be made in the vehicle owner’s manual as to the new tire size and recommended tire pressure. It is also recommended to make up an auxiliary tire placard with the new tire size and recommended tire pressures and place it adjacent to the OE placard.

BA

[Festus2]

Originally Posted by CWtheMan

Here is an abbreviated - by me - scenario of how to apply the vehicle manufacturers’ OE tire information when installing replacements of a different size, design or load capacity.

Once the desirable tires have been selected, correctly mounted, balanced and installed on the trailer a new recommended tire pressure must be determined. Using a load inflation chart for the replacement tires find the amount of tire pressure needed to equal the load capacity of the OE tires. That is your minimum acceptable tire pressure.

BA

CW -
Your scenario makes good sense in that you have removed all of red tape surrounding certification, regulations, and all of the other compliances out of the equation and what is left seems to be more realistic and practical - something we can and should all strive for.

Having said that, the load inflation chart that you refer to comes from, I assume, the tire manufacturer not from the vehicle manufacturer. And the last step of making a new placard to replace that provided by Keystone? The information on that decal would come from the tire manufacturer, not Keystone would it not?

As you have experienced, the tire topic is always "interesting" and not without controversy. Enough for one day.

[gearhead]

Not to beat a dead horse but:

"The replacement tires need to be able to provide as much load capacity (with air pressure) as the OE tires do/did."

I guess I need to take my Maxxis off and put my Towmax back on. Per both companies websites, the Towmax has 100 pounds more capacity than the Maxxis.
No. I don't think so.

[ocbms]

As most of you have found, Each RV seems to have axles and tires that nearly matches the maximum gross of the RV. That being said I carry the max pressure, 80 psig at about 60 degrees. When the morning temperature is 80 degree, I have over 80 psig. I also use a tire pressure monitoring system, don't drive other 65 mph and slow down if the tire pressure approaches 100 psi.
So Far so good for 3500 Trailer miles.

[Desert185]

I'm attending a gathering with a number of trailers and motorhomes in attendance. Since I've been on this forum I've been more aware of tire brands and air pressures and I am surprised at the number of aging and obviously under inflated tires I see. One trailer looked like one of the tires was down to 25 PSI. I asked a friend about his Maxxis tires on his 5er and he mentioned they were the original tires on the eight year old trailer.

To read some of these tire threads one could become seriously motivated to rid themselves of the "china bombs", buy a TPMS and religiously maintain 80 PSI. Seeing how many don't pay attention to their tires and are obviously complacent due to not having issues could counter that motivation, but I still can't take the chance on my Power Kings. Right now, Maxxis 235/80-16's are in the future before the next big trip. Even at 100# less per tire I'll still have tires capable of the 326's GVW.

[GMcKenzie]

Not wanting to argue tire pressure, but I still think the best way to be sure is to find an nice, open parking lot, make a chalk line across the tread of the tire and drive forward a few feet. Check how the chalk line is wearing off. If the center is wearing off, let some air out, if the outsides are wearing off, add air. It should wear off evenly.

Same goes for the truck tires.

[JRTJH]

Originally Posted by GMcKenzie

Not wanting to argue tire pressure, but I still think the best way to be sure is to find an nice, open parking lot, make a chalk line across the tread of the tire and drive forward a few feet. Check how the chalk line is wearing off. If the center is wearing off, let some air out, if the outsides are wearing off, add air. It should wear off evenly.

Same goes for the truck tires.

Unless there's a significant misalignment issue, I'd guess that less than 10% of RV owners will wear their trailer tires before their "time out" occurs at 5 years from DOM. Even if they are "overinflated" and riding on the center, most owners won't see enough wear to need replacement tires before they "time out".

It might seem like a "feel good" issue to compare chalk marks on the blacktop, but honestly, I'd think that balancing the tires and keeping maximum recommended inflation pressure will reduce heat buildup (tire enemy #1) by reducing sidewall flexing. Since the tires won't "wear out" for almost all of us, trying to keep the tread in even contact with the pavement isn't really that critical. Keeping the tire at maximum pressure seems ( IMHO) to be much more important.

Now, if you can accomplish "even tread wear" and "minimum heat buildup" you're on the right track.

[CWtheMan]

Originally Posted by Festus2

CW -
Your scenario makes good sense in that you have removed all of red tape surrounding certification, regulations, and all of the other compliances out of the equation and what is left seems to be more realistic and practical - something we can and should all strive for.

Having said that, the load inflation chart that you refer to comes from, I assume, the tire manufacturer not from the vehicle manufacturer. And the last step of making a new placard to replace that provided by Keystone? The information on that decal would come from the tire manufacturer, not Keystone would it not?

As you have experienced, the tire topic is always "interesting" and not without controversy. Enough for one day.

Actually tire inflation charts are all approved by the TRA. Tire manufacturers distribute them under their own name brand. In other words, the chart for any Michelin LT235/85R16E or Goodyear of the same size will both have the same chart figures. Likewise for any Goodyear ST225/75R15E or Maxxis of the same size.

Sometimes there is a disparity when a tire of the same size, such as the ST235/80R16E, is manufactured with three distinct load capacities, 3420#, 3500# and 3520#. When reading the certification label for any of those tires you will not find its load capacity there. Without any load capacity description all of those load capacities default to the lowest load capacity. That is one of the primary reason many 7000# axles are derated to GAWRs of around 6750#. I’ll post a picture below.

The auxiliary tire placard is approved to be filled-out by the tire installer and placed adjacent to the Original tire placard. It’s described in the Bridgestone/Firestone plus sizing SOP.

http://www.irv2.com/photopost/showfull.php?photo=22027

CW

[CWtheMan]

Originally Posted by gearhead

Not to beat a dead horse but:

"The replacement tires need to be able to provide as much load capacity (with air pressure) as the OE tires do/did."

I guess I need to take my Maxxis off and put my Towmax back on. Per both companies websites, the Towmax has 100 pounds more capacity than the Maxxis.
No. I don't think so.

Sometimes there is a disparity when a tire of the same size, such as the ST235/80R16E, is manufactured with three distinct load capacities, 3420#, 3500# and 3520#. When reading the certification label for any of those tires you will not find its load capacity there. Without any load capacity description all of those load capacities default to the lowest load capacity.

CW

[CWtheMan]

If you’re using ST tires - and almost every RV trailer with 6000# axles and below have them - you have to stop thinking car/truck tires and start thinking trailer tires. One of the most prolific builders of ST tires says 1/3 of their load capacity can be gone in three years. Why would the tire builder say that? To counter that they also say that ST tires are designed to run all day, every day at full sidewall air pressure. The trailer manufacturers almost always set recommended tire pressures for the ST tire at full sidewall pressures. None of the ST tires have mileage ratings. The are just going to normally age out unless you’re traveling a lot, then your mileage expectations should never exceed 20,000 miles with any of them. Abnormal tread wear is normally caused by something other than the tire manufacturer.

On one hand an owner says their trailer is too heavy for the axles and tires and on the other they are fooling around with tire pressures for tread wear of a smoother ride or because someone else uses such and such air pressure. I recommend getting a load inflation chart for your tires and see what a loss of 5 psi is costing you in load capacity.

Type, tire tread separation, into your computers search engine. There will be lots of references. You may be surprised to find how consistent the answers for the causes are.

BA

[bsmith0404]

Seems like I have read all of this before....maybe 3 or 4 times. Every time someone asks about tire pressures we go through it all over again. Everyone has their own opinions, some have done significant research to educate themselves. I have read more crap on tire pressures, load indexes, etc than I ever thought I would care about. I have checked websites of multiple tire manufacturers to the point of obsession. In the end, I think many of us are saying the same thing, just in a different way.

Tire installers are required by law to install tires that meet or exceed OE specs. The lawyers will get them if they don't and there is an accident that can be attributed to tire failure.

That said, here is what I take away from everything that we as consumers need to worry about. Your tires load capacity MUST meet or exceed the GAWR of your vehicle. Example if your GAWR is 6500 lbs (most likely a 7000 lb axle reduced to match tires) your tires must have a minimum load capacity of 3250. MINIMUM being the key word! Installing tires with greater capacities is not a problem as long as you have clearance and the wheels will support. If you read the tire pressure charts for your tires, they will indicate different load capacities at different pressures. Again, the MINIMUM air pressure required is what will match the capacity of the tire to the GAWR. Using the same numbers as the above example, if your tires require 65 psi to give 3250 lbs of load capacity, then that is the MINIMUM psi required. If your tires have max air pressure rating of 80 psi on the sidewall for a greater max load, nothing stops you from going to the max. Increasing the tire pressure to max (recommended by most manufacturers for ST tires) increases their load carrying capacity and reduces heat and tire fatigue. Bottom line, make sure you are hitting all of the MINIMUMS, but it's okay (and many will agree it's best) to exceed them.

[TomHaycraft]

Originally Posted by bsmith0404

Tire installers are required by law to install tires that meet or exceed OE specs. The lawyers will get them if they don't and there is an accident that can be attributed to tire failure.

I had to chuckle when reading that and reflecting back on my tire purchase for the trailer earlier this year. I bumped up from the OEM Load Range C to Load Range Ds. Same physical dimensions of the tire. Discount Tire Company, where I purchased and had them mounted (and balanced with TPMS sending units attached!), made it very clear that I was altering the OEM specs for the vehicle. I'm sure a requirement from corporate based on whatever laws, but they made it very clear that I had changed from OEM specs.

The sales person at DTC and I had a good laugh, he knew I was stepping up for a larger margin of safety and thanked me for being patient as he went through what was required of him.

[bsmith0404]

Originally Posted by TomHaycraft

The sales person at DTC and I had a good laugh, he knew I was stepping up for a larger margin of safety and thanked me for being patient as he went through what was required of him.

Gotta love what the lawyers have turned this industry into. I understand if someone is downgrading, but when we have to be warned about the "dangers" of buying a tire that exceeds OE specs it has become ridiculous!

[CWtheMan]

Originally Posted by bsmith0404

Gotta love what the lawyers have turned this industry into. I understand if someone is downgrading, but when we have to be warned about the "dangers" of buying a tire that exceeds OE specs it has become ridiculous!

OK, here goes - once the mods get bored with my dialog in this thread just say so and I’ll quit.

Tire fitments for RV trailers get super complicated when it becomes time for replacements. RV trailer axles are fitted with Special Trailer (ST) tires 90% (+/-) of the time. Most first time trailer owners are not familiar with the ST tire design.

The replacement tire fitments for our normal everyday motorized vehicles differ tremendously from RV trailer tire fitments. That’s mostly because the tire industry, in collaboration with the automotive industry, develop lists of replacement tire options for our automotive vehicles. You drive into a tire retailer’s business, the tire sales person gets the information about your vehicle and offers you a selection from the list of tires available for your vehicle. Unless you’re going way out in left field there will also be a list of approved plus sized tire selections. That is not going to happen with your trailer tires. There are no lists. The primary recommendation for replacement tires will come from the trailer’s manufacturer. Here is a verbatim paragraph from the Keystone generic owner’s manual dated 4/14.

“To maintain tire safety, purchase new tires that are the same size as the vehicle’s original tires or another size recommended by the manufacturer. Look at the Tire and Loading Information label, or the sidewall of the tire you are replacing to find this information. If you have any doubt about the correct size to choose, consult with the tire dealer.”

Unless there are tire options in your individual owner’s manual that statement rules, so to speak. That statement help’s a little in explaining Discount Tires’ explanation of going up in load capacity. The logic is that the tire size on the certification label may say something like ST225/75R15D, that is then the official size of the OE tires. To replace them with a ST225/75R15E is a physical change. The most significant part of the change is the ability of the replacement tire to hold 80 psi vice 65 psi for the OE tires.

The bottom line about replacement tires is the tire industry standards. The DOT, via its subordinate divisions have given the sole responsibility of tire selection and fitment to the vehicle manufacturers. The tire industry standards are written to support that decision by the DOT and also to avoid outrageous law suits.

CW

[Festus2]

Originally Posted by CWtheMan

OK, here goes - once the mods get bored with my dialog in this thread just say so and I’ll quit.

CW

CWtheMan -

The last word belongs to you.

[Desert185]

CWtheMan:

Given your experience, give me a replacement tire recommendation for my signature 5er (235/80-16).

Curious...