RV Trailer Tires

[CWtheMan]

I spend a few hours every week on ST tire researching. This week it's been TBC Brands.

The Towmax name on ST tires has almost always been viewed as a warning. Here again, you can see the reengineering of China made ST tires is always in progress.

You could bet it wouldn't be long for the China ST market to emulate the GY Endurance ST line-up.

The new Towmax long name is; Power King Towmax Vanguard. The tires will be touted as Towmax Vanguard. For this TBC endeavor I would describe Vanguard as; "a group of people leading the way in new developments or ideas." Actually it looks like sealing to me.

Here is an excerpt from their product introduction pdf. ""The Towmax Vanguard was designed to be the industry standard by combining an array of features to provide consumers a unique quality and performance proposition. The tire features decoupling grooves and an optimized tread depth to reduce rolling resistance and heat buildup extending the life of the tire while large shoulders and an extra wide tread face provide even load distribution and stability through a larger contact patch. The nylon overlays used on all sizes help achieve an 87 mph maximum speed rating and ensure improved towing stability and high speed durability. To maintain the tire’s appearance and decrease sidewall damage, the Towmax Vanguard also features scuff protectors."

[CWtheMan]

Tredit is one of Keystone's major OEM provider of tires. If you explore their web site you'll probably find some brand names you're not familiar with.

But, I'm not posting this in support of any particular brand. However, I'll have to mention a name brand to describe what I think is a very good option for those of you boondocking with tag along trailers. Rainier has a new - about a year now - ST tire design that just may get your interest. It's described in the reference below.

https://www.tredittire.com/tire/rainier-st-apex/

[CWtheMan]

In no way does the use of a tire brand name in my posts constitute anything other than tire industry information. The China ST tire manufacturers are very responsive to the needs and desires of the RV trailer community.

Just about all of the most productive China ST tire manufacturers are now building the popular 16” all steel ST tires in two designated sizes and they are all LRG.

TransEagle – in the link below – has added a 15” all steel ST tire to their line-up. It is the ST225/75R15 and it has two load ranges, LRF & LRG.

http://transeagletires.com/

Carlisle has added the 15” LRF to their all steel ST tire listings (CSL).

https://www.carlislebrandtires.com/o...-detail/csl16/

TowMaster by Greenball have also added the 15” LRF steel tire to their line-up.

https://www.greenballtires.com/brand...tow-master-asc

[tech740]

Seems they are reacting to customers going up in load carrying safety margin. They are realizing they were not really in this game and giving options. Like anything else we will see what the next three years brings to determine reliability.

[CWtheMan]

Originally Posted by tech740

Seems they are reacting to customers going up in load carrying safety margin. They are realizing they were not really in this game and giving options. Like anything else we will see what the next three years brings to determine reliability.

Actually I'm going to view it as providing load capacity reserves. Wise consumers have always been screaming for those reserves. And, increased load capacity to meet the RVIA recommendation for load capacity reserves 10% above GAWR.

7000# vehicle certified axles are now being fitted with tires that will provide, at the very minimum, 3850# of load capacity. The ST235/80R16 LRG is the ideal fit.

8000# vehicle certified axles are now being fitted with tires that will provide, at the very minimum, 4400# of load capacity. The ST235/85R16 LRG sneaks' in that door with 4400# of load capacity @ 110 PSI.

With all these tires having increased load capacities there is no need to worry about changing designated size with replacements. For instance, the ST235/80R16 has 3 usable load ranges, LRE, LRF and LRG. The ST225/75R15 has 5 usable load ranges, LRC, LRD, LRE, LRF and LRG. Somewhere in those load ranges a consumer can satisfy his requirement for adequate load capacity reserves with replacement tires without having to change the designated size.

[tech740]

I have the ST235/85-16 LRF now. In the spring I will take them to LRG for more reserve. I have 7k axles.

[CWtheMan]

Originally Posted by tech740

I have the ST235/85-16 LRF now. In the spring I will take them to LRG for more reserve. I have 7k axles.

This is just a personal request for information on your trailer. Keystone very seldom provides axles with load capacity reserves. It invites trailer overloading. So my question is; Does your trailer's federal certification label list the GAWRs as 6600# or 7000#? At 7000# they would technically support a GVWR of 16500#, a 1000# over the certified GVWR.

I have noted that other Keystone trailers now have axle load capacity reserves and I'm wondering if that's a new Keystone axle standard? Our annual local RV show is next month and I'll be photographing certification labels on all Keystone trailers at that show.

Here's a Keystone certification label from the past that has matched the GAWRs to the installed OE tire maximum loads.



Note: The axle manufacturer's certification on those installed axles in the reference above was 5200#.

[gearhead]

Originally Posted by CWtheMan

This is just a personal request for information on your trailer. Keystone very seldom provides axles with load capacity reserves. It invites trailer overloading. So my question is; Does your trailer's federal certification label list the GAWRs as 6600# or 7000#? At 7000# they would technically support a GVWR of 16500#, a 1000# over the certified GVWR.

I have noted that other Keystone trailers now have axle load capacity reserves and I'm wondering if that's a new Keystone axle standard? Our annual local RV show is next month and I'll be photographing certification labels on all Keystone trailers at that show.

Here's a Keystone certification label from the past that has matched the GAWRs to the installed OE tire maximum loads.

Attachment 30526

Note: The axle manufacturer's certification on those installed axles in the reference above was 5200#.

Is a 5200# axle the same as a 6000# axle? Internally at least? I'm assuming the springs could be different.

[CWtheMan]

Originally Posted by gearhead

Is a 5200# axle the same as a 6000# axle? Internally at least? I'm assuming the springs could be different.

Actually its what the axle manufacturer certified it to be. It's certified to the weakest link. Items included with the axle that may have higher load ratings are providing load capacity reserves in that area.

Don't forget. The vehicle manufacturer has the authority to lower the axle manufacturers certification to an appropriate value to meet vehicle GAWR minimum requirements. The certification label on RV trailers is considered to be a final stage certification. It takes precedents' over all other items certification values.

[gearhead]

My interpretation of that is...they could re-rate a 6000# axle to 5200# which would still get them to reserve capacity and be able to put lower rated cheaper tires on it?

[tech740]

Mine is a Forest River but I am sure they use the same standards.

[CWtheMan]

Cargo capacity and trailer loading is a common subject in RV Trailer forums. The FMVSS standard 571.120 is one of the standards RV trailer manufacturers must comply with when building your trailer. Actually, the Trailer manufacturer does not have the final say about the maximum load your trailer can carry according to it's cargo capacity. That responsibility falls to the original selling dealer of the vehicle. If they install any options that total over 100# they MUST deduct the value from the label and provide a corrected copy at the time of first sale.

Sometimes really unhappy consumers are looking for answers about their trailer having too little cargo capacity. There is no relief as long as the manufacture’s listed cargo capacity does not cause overloading of the trailer’s GVWR. The following paragraph is from a NHTSA document that addresses what the vehicle manufacturer’s responsibilities are.

"The FMVSS have requirements for the manufacturer to use proper tires and rims for the gross axle weight rating (GAWR) and the gross vehicle weight rating (GVWR). The manufacturer may determine the GVWR by adding cargo capacity (if any) to the curb weight of the vehicle as manufactured. The wise consumer, before purchase, will determine if the vehicle has sufficient cargo capacity to carry the weight of water, additional equipment (such as televisions, and microwave ovens), and luggage. The manufacturer’s certification label must show the GVWR. The GVWR must not be exceeded by overloading the vehicle. There is little the government can do to assist a consumer who has purchased a vehicle that has insufficient cargo capacity for its intended use."

[CWtheMan]

With more and more steel cased radial tires being used on our RV trailers it becomes very important to become knowledgeable of the Zipper Rupture and how to visually inspect your steel cased tires.

Under inflation is a primary cause of Zipper Ruptures. If for some reason you find a steel cased radial tire at 80% of the normal recommended cold inflation pressure, it’s very possible that tire has entered into a zipper rupture condition and should be dismounted and inspected internally as well as externally.

When visually checking your steel cased radial tires during your walk-around, look for telltale small wires protruding from their sidewalls.

It doesn’t just happen to RV trailer tires. It happens to all steel cased radial tires.

Here's a picture. Very dangerous if you're standing there when it explodes.



The current steel cased radial RV trailer tires used as OEM on our trailers are listed below. My list may not include all of them.

LT235/85R16 LRG RST
ST235/80R16 LRG
ST235/85R16 LRG
ST225/75R15 LRF & LRG

As they become a more desirable RV trailer tire, I’m sure the off shore ST tire manufacturers will introduce more sizes with radial steel casings ( AKA, All Steel).

[gearhead]

Yeah Discount is my default go to tire shop.

[CWtheMan]

ST tire failures

You know, I’ve been writing about RV trailer tires for more than 17 years. I’ve explored, reviewed, researched and written about thousands of tire failures that occurred while in use as RV trailer tires. Many of my conclusions are drawn from multiple failures from single causes although unknown by the consumer.

When reading this please take into account that I’m a serious study of the rules, regulations and standards used by the industries that have approved the tires for use as high speed trailer tires. I’ve read ever DOT/NHTSA tire rules committee report, approval/disapproval since 2003. I’ve read some of them so often I can reference them without rereading them (again).

The evolution of ST tires used on our RV trailers is directly linked to the needs of the trailer industries. As more and heavier trailers were built, the ST tire manufacturers were being driven to provide more designated sizes and load ranged tires to support the demands of the trailer industries. Because of import/export rules, almost all of the off shore ST tire manufacturers have always had a huge advantage in pricing, which (IMO) caused almost all of the USA manufacturers to not waste their time building tires that were going to be very difficult to sell to a market that had numerous tires on their USA shelves at much lower prices.

The Tire and Rim Association (TRA), an organization with approval authority for the construction and standardization of the ST tire design, set a 65 MPH maximum operational speed restriction for all ST tires. Because there is no official speed letter for 65 MPH, there was no authority to force those manufacturers to provide that information on the tire sidewalls.

Enough lead-in info, let’s get to the meat of the posting. I’ll add references as I go from here.

So, where do RV trailer manufacturers get the tire/wheel assemblies, suitable for fitment to specific RV trailer axle loads? They get them from suppliers of OEM equipment. The tire is from a tire manufacturer and the wheel from a wheel manufacturer. The tire manufacturer provides the installers with approved rim sizes for the tires. Load and PSI needs will be provided by the needs of the axles they are earmarked for. Yup, were getting to some of the meat. The OEM provider will almost always assemble the wheel/tire assembly to a request made by the vehicle manufacturer. If the vehicle manufacturer’s request has not provided a PSI setting for the assembly, the tires will normally have the PSI value used to set the bead. If the factory installer fit's that assembly to an axle without a PSI request from where it’s going to be fitted to a vehicle, it will still have that bead setting PSI in it. Eventually, as the trailer progresses along the production line the tires will become overloaded. If at final vehicle certification the pressures are not increased to recommended cold inflations for the fitment, the trailer will be turned-over to a delivery agent. Will the agent inflate to recommended cold? The tire damage started just as soon as it became overloaded. It could then be more severely damaged by being severely under inflated for transport and having its delivery speed increased beyond 65 MPH. Once at the dealer location it will continue to degrade from overloading until someone discovers the under inflated tires. The damages have been done. Tire damages are cumulative. Those tires are going to fail long before their predicted life span. Maybe that will happen on the way to their new home.

If you want an installment 2,3,4 etc.. Let me know. I’ve just barely got in the door

[gearhead]

^Go for it..

[CWtheMan]

When a consumer has the luck to get a new trailer without some sort of tire damage, the ST game begins.

Consumers new to ST tires will make a lot of mistakes trying to properly maintain them. It’s much more complicated than maintaining tires on an automotive product. Although RV trailer tires and automotive tires conform to the same standards, there are major differences. Those differences are argued constantly in RV trailer forums. The first difference causes the most problems resulting in early ST tire failures, some catastrophic. RV trailer tires are not required to have load capacity reserves. All automotive tires must provide a percentage of load capacity reserves. Throughout the RV trailer industry its common knowledge that RV trailer axles are notoriously unbalanced. It can be an entire axle load imbalance or a single tire position imbalance. With tires providing zero load capacity reserves those imbalanced tires have a very high probability of failing and failing very early. I’m going to add a picture of a Keystone trailer’s certification label that depicts its GAWRs being set (by Keystone) at 5080# so the tires shown on that certification label can be used. Those tires provide – do the math - 2540# of load capacity at the PSI value, also shown on the certification label. The probability of having at least one tire severely overloaded on that trailer is very high.

Basically, the speed rating is telling us the tire can carry its maximum load capacity depicted on its sidewall. As the speed is increased beyond the speed rating the tire will overheat and start to degrade. Each time it degrades it’s added to the previous degrade. We had zero load capacity reserves and the degrading is eating away at the tires maximum load capacity. Something has to give.

A few years ago our government (USA) threatened most of the off shore manufacturers with increased tariffs if they did not mold a speed rating or speed letter to the tire sidewall. Although the load index system is not the official load indicator for LT & ST tires the load index system is used to display tire speed letters. (There is no letter for 65 MPH). The agency tasked with the responsibility of insuring that speed rating/letter is on the tire is US Customs. The only ST tire I know of that does not have a speed rating is Maxxis. According to TRA, an unmarked tire defaults to 65 MPH, no excuses allowed.

The regulation/standard allowing minimum tire load capacity equal to the GAWR has not changed. However, a few years ago (2017) RVIA, a large private membership organization mandated that all participating members (about 98% of all RV trailer builders) provide Original Equipment tires with the ability to provide at least 10% in load capacity reserves above the vehicle certified GAWRs. That RVIA recommendation will de facto effect all replacement tires recommended load capacities. That’s because of the industry wide standards that require all replacement tires to have a load capacity equal to or greater than what the OE tires provided.

[gearhead]

So mechanically speaking, are the increased failures when going over the rated speed due to increased frequency of sidewall flex, belt separation, or ?

[CWtheMan]

Originally Posted by gearhead

So mechanically speaking, are the increased failures when going over the rated speed due to increased frequency of sidewall flex, belt separation, or ?

When it comes to tire mechanics I rely on the more experienced posters like Tireman9 for answers. From my point of view, tires are going to start degrading when subjected to speeds greater then what they were designed to resist.

Speed ratings for ST tires have become very controversial since they started using ratings higher than 65 MPH on their sidewalls. Because I don’t have access to confidential TRA manuals I cannot argue with those that do. However, from knowledge of how the systems work, I find it very improbable that the largest tire manufacturer in the world (GY) would introduce a completely new line-up of ST tires and give them a speed rating of 87 MPH without NHTSA approval. Somewhere in that process NHTSA was assured by GY that their new line-up was tested for the 87 MPH limit.

As for a tread separations, who knows, they are normally caused by numerous misuse factors. Sidewall flex is another engineering subject. Each tire design (ST - LT – P) is different and tested for different factors to correspond with their expected usage. However, they can all be used on RV trailer axles. That’s a decision only the trailer manufacturer can make for OE tires.

[CWtheMan]

Tire selections: Is it done by monopoly, supply and demand, design characteristics, popularity, low bidder or just plain old money. Probably some of those are in combinations.

Whatever the madness is, it all boils down to the individual manufacturer. They have the sole responsibility for Original Equipment tire selections and fitments on their vehicles and in the end they MUST certify those selections. The vehicle manufacturer has the option to use any of the DOT approved highway tires. They can also offer a limited number of options. Once they make the final decisions don’t try to get them change designations or designation sizes. It’s not going to happen. It would mean they made an error and such an error could cause them initiate a recall. Recalls are expensive and are, at all costs, avoided by vehicle manufacturers. However, brands with the same designated size as the OE tires can be requested from dealers because there are no certifications required to do so.

That sort of leads me into designated sizes. In the NHTSA 2010 rules committee meeting, they approved that all tires are to be referred to by designated size. ST235/85R16 is a designated size. LT235/85R16 is a different designated size. In the eyes of tire regulations and standards they are not interchangeable, even when used as a plus size.

To understand the why, requires an understanding of precedents. Senior government regulations provide the information their underlings MUST follow. 49 CFR (a code of federal regulations) sets the stage for the use of designated tire sizes. So, when the vehicle manufacturer applies the standards in FMVSS – standards they must use to build trailers – they mention designated sizes in the fitment applications. FMVSS (standards) are minimum in nature, therefore, the tire designated sizes found on the vehicle certification label and their recommended cold inflation pressures are minimum standards. When one looks at the tire industry standards for replacement tires they clearly say that replacement tires MUST have a load capacity equal to or greater than what the OE tires provided.

NOTE: Within the 49 CFR tire document; using a designated size that differs from the certification label is cause for rejection. (No one can disregard that without violating a safety standard).

In the automotive industry, vehicle manufacturers provide listings of recommended designated tire sizes for replacement of the OE tires. In the RV trailer industry that procedure doesn’t exist. NHTSA, in its wisdom, has mandated that a statement about tire replacements MUST be in all RV trailer owners’ manuals. Here is a verbatim quote from the Keystone manual.

“To maintain tire safety, purchase new tires that are the same designated 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.”