Weight & tire PSI question

[FastEagle]

OK, here is the dilemma as I see it.

The first stage manufacturer (chassis) may have used FMCSA regulations in their description of tire inflation.

The final stage manufacturer’s regulations/standards will supersede the FMCSA regulations if the final stage manufacturer certified the vehicle in accordance with the standards in FMVSS. FMVSS standards require the vehicle manufacturer to set a recommended cold inflation for the installed tires that are Appropriate for the fitment. In doing so they defacto set a minimum standard.

So, does your RV have a certification label/tire placard that has recommended cold inflation pressures displayed on it?

All of the major tire manufacturers are members of the referenced web site below.

Starting on page #49 (Proper Tire Inflation) and reading all the way to the bottom of page #51 you will find the proper procedures for RV tire inflation in accordance with FMVSS standards.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf

[Crasher]

I do not have a dilemma.Yes my coach has a placard setting the "safe" psi. However, as I said previously, the amount stated left the steer tires underinflated (unsafe) for the actual load. Also included with the coach were explicit instructions from the Tiffin and Michelin to weigh each position and refer to the load chart for the correct pressure. Neither one made reference to the placard. It doesn't get much simpler than than.

Edit: If someone places all of their trust in the FMVSS, then I can see how they would have a dilemma. We all have to make choices. I choose to put my trust in the people that built the coach and the tires.

[kedanie]

The unfortunate thing here is that the "Tire Experts" put all their faith in the government documents. They are blind to the obvious. Seems that they believe that the the government is right no matter how wrong they are.

Keith

[Crasher]

Originally Posted by kedanie

The unfortunate thing here is that the "Tire Experts" put all their faith in the government documents. They are blind to the obvious. Seems that they believe that the the government is right no matter how wrong they are.

Keith

To me, the bigger question is why does the FMVSS come up with a formula that all manufacturers are supposed to follow that produces a number that is supposed to fit all loads in a motorhome? Close to 100% of all coaches will have vastly different loads depending on the owner's loading. I wonder how many if any of the people that came up with that formula have ever been in a motorhome, much less owned and driven one? It's only common sense that the tire manufacturers would know their product better than some officials in a room deciding what pressure to attach to a placard. If I have a toothache, I go to a Dr that knows something about teeth. Of course, maybe some government agency would know better.

I know I should just walk away from this very important topic. There are some who will never understand the concept of weighing each position and following the load inflation charts. For them, following the placard psi is better than no plan at all. For those who accept the FMVSS number as correct, go for it.

[kedanie]

Yep, the "Tire Expert" has zero experience with motor coach tires. His basis of knowledge comes from ST tires used on 5th wheel trailers. He seems to believe that the government is right no matter what!

Keith

[Tireman9]

Originally Posted by Crasher

To me, the bigger question is why does the FMVSS come up with a formula that all manufacturers are supposed to follow that produces a number that is supposed to fit all loads in a motorhome? Close to 100% of all coaches will have vastly different loads depending on the owner's loading. I wonder how many if any of the people that came up with that formula have ever been in a motorhome, much less owned and driven one? It's only common sense that the tire manufacturers would know their product better than some officials in a room deciding what pressure to attach to a placard. If I have a toothache, I go to a Dr that knows something about teeth. Of course, maybe some government agency would know better.

I know I should just walk away from this very important topic. There are some who will never understand the concept of weighing each position and following the load inflation charts. For them, following the placard psi is better than no plan at all. For those who accept the FMVSS number as correct, go for it.

As a real tire "expert" (40 years experience as tire design and quality engineer and recognized by DOT as an expert in failed tire examination) I think I can provide some clarification.

FMVSS regulations do not have any "formula" for load & inflation. They always defer to the published tire industry tables as found in the Tire & Rim Association Yearbook (similar tables are available for tires manufactured in other countries.) These tables are assembled by engineers at the various tire companies and accepted by a group of representatives before the numbers are included when a new size is developed. The numbers in the tables almost never change. (I don't think they ever do unless there is some other change in the tire size or designation)

The regulation the RV company is suppose to follow is that the inflation specified on the certification sticker/sheet must be sufficient to support the GAWR. This assumes the unrealistic perfect 50/50 side to side load split.

Tire companies are suppose to certify that all the tires they sell are capable of passing some short drum test run in a laboratory. I am confident that the "top Tier" brand tires are built with that goal in mind and tires are being constantly tested to confirm that there has not been any "drift" in product quality. You can read about the tire Tiers HERE.

IMO there are many working at DOT that are not "Tire Experts" as there are no college degrees in real life tire design, only OJT, and there is not much incentive to move from Akron to Washington D.C.
There are advanced courses in tire theory or advanced polymer chemistry but to my knowledge none of those classes ever require the student to have mounted a tire or even to have driven a variety of vehicle types so yes, real life experience is missing.

IMO, following regulations is a good approach in many jobs such as aircraft maintenance but simply reading and following published regulations does not encourage innovative thinking on how to make and implement improvements, nor does it qualify one for being able to conduct a forensic examination and to then develop new guidelines or regulations.

Following the Certification label is reasonable but I have personally seen more than one label that is in violation of the regulations or contains mistake so IMO knowing the actual weight on each tire position and following the table inflation and adding +10% inflation for a margin would be my recommendation for a "Best Practice".

[FastEagle]

Tireman9

It's important to know if you support the statements outlined in this portion of my previous post;

Starting on page #49 (Proper Tire Inflation) and reading all the way to the bottom of page #51 you will find the proper procedures for RV tire inflation in accordance with Tire Industry Standards.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf

It's the vehicle owner's responsibility to insure their vehicle is operated safely. In this sort of post that includes the proper weight and balance of the vehicle. I've not disputed that fact. However, the "weight to load carried" is often disputed by manufacturer's of so called RV tires. Toyo was one of the first to do that. The CEO of Toyo is also a CEO of the US Tires Manufacturers Association. Their publications clearly say to never use less tire inflation pressures than what has been recommended by the vehicle manufacturer.

The "inflate to the load carried" is not a subject discussed anywhere in FMVSS Standards. FMVSS standards are minimum standards vehicle manufacturers must follow. Therefore they are not binding for vehicle owners. But, we, as owners, cannot apply those minimum standards because we are not the vehicle manufacturer or tire builder. Tire industry standards will follow the minimum safety standards written in regulations from NHTSA. Without load capacity reserves we could not have active TPMS.

[Crasher]

Here we go again. I'm glad I'm leaving in the morning for our AZ home and will not be on here for a week. If I'm lucky, this thread will have faded into the sunset by then.

[kedanie]

All these posts about federal standards, manufacturer standards and who knows what other standards the "Tire Experts" want to throw out there.

Really?!! Who really cares, none of it applies to the end users. All that is being done is to confuse the innocent and upset those that know the difference. Get off your soap box and talk about something that you have some real world experience with. Perhaps sell some more ST tires. When you have some real life first hand experience with Motor Coach tires then maybe folks might believe you.

Keith

[Tireman9]

Originally Posted by kedanie

All these posts about federal standards, manufacturer standards and who knows what other standards the "Tire Experts" want to throw out there.

Really?!! Who really cares, none of it applies to the end users. All that is being done is to confuse the innocent and upset those that know the difference. Get off your soap box and talk about something that you have some real world experience with. Perhaps sell some more ST tires. When you have some real life first hand experience with Motor Coach tires then maybe folks might believe you.

Keith

Have you ever considered checking the "Resume" of the folks presenting themselves as "Tire Experts"?

[Tireman9]

Originally Posted by FastEagle

Tireman9

It's important to know if you support the statements outlined in this portion of my previous post;

Starting on page #49 (Proper Tire Inflation) and reading all the way to the bottom of page #51 you will find the proper procedures for RV tire inflation in accordance with Tire Industry Standards.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf

It's the vehicle owner's responsibility to insure their vehicle is operated safely. In this sort of post that includes the proper weight and balance of the vehicle. I've not disputed that fact. However, the "weight to load carried" is often disputed by manufacturer's of so called RV tires. Toyo was one of the first to do that. The CEO of Toyo is also a CEO of the US Tires Manufacturers Association. Their publications clearly say to never use less tire inflation pressures than what has been recommended by the vehicle manufacturer.

The "inflate to the load carried" is not a subject discussed anywhere in FMVSS Standards. FMVSS standards are minimum standards vehicle manufacturers must follow. Therefore they are not binding for vehicle owners. But, we, as owners, cannot apply those minimum standards because we are not the vehicle manufacturer or tire builder. Tire industry standards will follow the minimum safety standards written in regulations from NHTSA. Without load capacity reserves we could not have active TPMS.

Interesting document. I do note it has a situation, pg 51, that seems to suggest some RV companies are not following FMVSS.

RMA says "Determining Proper Inflation Pressure - With actual weights of the loaded RV acquired by weighing, it is possible to compare them against the GAWR, GVWR, and tire capacities posted on the vehicle tire placard or certification label. These actual weights are also what should be used to determine any increase in inflation pressure for the tires, if required. "

But if the certification label complies with providing the inflation level that will support the GAWR then if the actual weights indicate an increase in inflation above the placard then by definition if the owner needs to exceed the placard inflation to meet the load/inflation requirement then the RMS is advocating that exceeding the GAWR is acceptable ???

Thanks for bringing this to my attention. I will be contacting RMA and asking how they reconcile this aparent conflict.

[kedanie]

Originally Posted by Tireman9

Have you ever considered checking the "Resume" of the folks presenting themselves as "Tire Experts"?

A little sensitive?

We all know who the pretend "Tire Expert" is around here!

So who is the enforcement agency for all the thousands of RV owners out there through no fault of their own who are in violation of your precious Federal Standards? I, for one have never heard of or seen any!

Once again, all this paper you guys are throwing in our faces is intended for the manufacturers and is meaningless to the end users out there!

Go preach to the manufacturers and leave us commoners alone.

Keith

[Pipefiter]

Dash camera monitor for rear camera fluctuates with bulbs.How do I pull it out of dash to check wires.I have a2013 canyon star.

[cinergi]

Came across this video today and thought of this thread. I have no official stance one way or the other but thought this might be useful information. It's a Michelin video about tires in an RV application and at least once (I think twice) directly says to set the tire pressure based on load. e.g. 6:00 - 6:20 in the video.

https://www.youtube.com/watch?v=Wb7W-nRAPrk