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Old 12-19-2017, 07:29 PM   #1
CWtheMan
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RV Trailer Tires

A synopsis: My version of RV trailer weights, tire & axle fitments simplified.

Although automotive vehicles and RV trailers are governed by the same building regulations and standards the weights may differ. The one undisputed weight is the vehicle’s GVWR. It is the maximum acceptable operating weight specified by it’s manufacturer.

Because axle manufacturers do not manufacturer axles in weight increments that will coincide with a vehicle manufacturer’s needs, the vehicle manufacturer has the authority to set GAWR weights that differ from the axle manufacturer’s certified GAWR. Example; Your trailer’s axles may have a tag on them from their manufacturer certifying their maximum load as 4000#. The trailer manufacturer can derate them to 3700#. It’s commonly done to allow the fitment of tires. In this case it could be they want to use ST215/75R14C tires because of their load capacity and diameter. Bottom line; The vehicle manufacturer’s GAWR values supersedes the axle manufacturers values and are the official certified values for that fitment.

Tires fitted to RV trailer axles must provide a load capacity equal to or greater than the certified GAWR of the axle (s). RV trailer manufacturer’s are required to set a recommended inflation pressure for those tires that is appropriate for their fitment.

Tire and axle fitments for RV trailers differ from automotive vehicle fitments because of the way the regulations and standards are written. Load capacity reserves are not a requirement for RV trailer tires or the axles they are fitted to. Their only requirement is to have load capacities equal to the tasks they are required to perform.

In the automotive industry axles and tires must provide a percentage of load capacity reserves. Their builders can do that with the axles/tire fitments or both. Look on your tow vehicle’s certification label and you will find that when the GAWRs are added together, they exceed GVWR. GVWR is the limiting factor so the axel overage is load capacity reserves. The tires may also have some load capacity reserves but not always. Rear tires may be maxed-out (inflation wise) but the axle’s load capacity reserves prevents the tires from being overloaded.

Tire industry standards for RV trailer tire replacements pretty much supports 100% of the building regulations that are certified. Because the building regulations are providing a minimum safety factor the tire industry standards will not do less. So, replacement tires must have a load capacity equal to or greater than the Original Equipment tires. That’s the way it’s written, but, there are other factors. Tire design. There are antiquated DOT regulations that are still active and are or can be applied at any time. They set a precedent that disallows changing tire designs from the trailer manufacturer’s OE tire design. It’s why it’s called a misapplication and also why almost any reputable tire retailer will refuse to make the swap. There are exceptions, LT tires designated RST (Regional Service Trailer). Any tire designed for low platform trailer service. Those are mostly 17.5” tires. Some European/Asian commercial tires designed for trailer service.

Because a trailer manufacturer uses something other than ST tires on a specific model or series of models does not imply that design can be used on some other model (s). The vehicle manufacturer has the sole responsibility in tire fitments and the tire design for such fitments. If a trailer manufacturer’s normal fitments are ST tires, with an optional design offering, that offering ends when the trailer is certified. Final certification ends before the vehicle is signed over to a consumer/owner. (Under some circumstances an authorized dealer is allowed to change the certification label prior to first sale, but only with the consent of the trailer manufacturer).

Today’s RV trailers, from the smallest to the largest, have more storage space than ever before. They can easily be overloaded long before all the storage spaces are used-up. It takes a wise and dedicated owner to be diligent enough to manage their trailer’s loads and how they are balanced.

Going back to those ST215/75R14C tires. They provide 3740# of load capacity for a 3700# axle. RV trailer axles hardly ever have a balanced load, so it’s very possible that one of those tires is going to be overloaded all the time. Only a savvy owner that often goes to a set of scales for load balancing can come close to being successful at keeping those tires from failing, early. (Early being a couple of years).

Remember, brochures are not official documents. They may have accurate information but not 100% of the time. Information in the vehicle owner’s manual is official. It was mandated by NHTSA. It should always be your guide over and above what is said in writings such as this.

I know all about what so and so said. “What is good for the goose is not always good for the gander.”

Reference material:
FMVSS
CFR 49 part 567
US Tire Manufacturing Association
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Old 12-19-2017, 07:48 PM   #2
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Wow !

I did not know there were so many words about tires . . . . .

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Old 12-19-2017, 08:41 PM   #3
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Well, this should become interesting
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Old 12-19-2017, 09:20 PM   #4
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Quote:
Originally Posted by Sherwolfe View Post
Well, this should become interesting
I agree, my 5er came from the factory with LT tires 235/85-16E’s, 3,042# ea capacity 12,168# total on a 32’ 5er with a GVWR of 12,360# that is plenty in my book. The originals were 12 years old when I replaced them last summer.
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Old 12-20-2017, 03:11 AM   #5
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Okay, I'll start it.
"The originals were 12 years old when I replaced them last summer."
I'm not sure I would have admitted this.
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Old 12-20-2017, 05:09 AM   #6
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Originally Posted by notanlines View Post
Okay, I'll start it.
"The originals were 12 years old when I replaced them last summer."
I'm not sure I would have admitted this.
Why not? They were LT's still in very good shape, always covered and the last couple of years most of our trips were about 150 miles.
I see so many post on here of those running ST tire get a blowout thinking back to maybe hitting a curb, or a bad set of tracks. Heck these tires did this many times and still preformed great.
So many on this site are so happy to get a set of ST tires for their 5er and pay less then $400 for a set of four, then bitch like crazy when one blows after a year of service. I paid over twice that for a quality set of LT same size and weight capacity as the OEM LT tires.
I see all this talk of the ST being "Special" to deal with the scuffing when turning. Well I don't buy that, had a neighbor that ran log truck for years, ran the same casings, be it be steer, drive, or trailer position. When drivers got worn a bit and still had ok tread depth, but traction was down, those were moved to trailer position, then when tread was worn out, they were capped. Could be capped for either drivers or rib tread for trailer use.

Just my personal experience.
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Old 12-20-2017, 03:09 AM   #7
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Mine came with axles rated at 2K more than the GVWR and with tires rated at 5480# more than GVWR, so figure that one out...not complaining though!
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Old 12-20-2017, 09:57 AM   #8
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Originally Posted by Tinner12002 View Post
Mine came with axles rated at 2K more than the GVWR and with tires rated at 5480# more than GVWR, so figure that one out...not complaining though!
Keystone has always been better with fitments for triple axle trailers. There is probably money involved with your trailer's axle, wheel & tire fitments. Those ST tires are much less expensive than the 16" LRG RST tires or the 17.5" tires used for such fitments before the strictly Asian 16" LRG tires hit the market.

Does your trailer's certification label list your axles as 7000# GAWR? Just curious. Usually RV trailer builders do not want to invite consumers to overload the trailer's GVWR.
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Old 12-20-2017, 10:16 AM   #9
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My tires are rated 2540# each single. My axles are 4400# and my GVWR is 10,000# seems like I need more axle
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Old 12-20-2017, 10:49 AM   #10
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Originally Posted by IRV2 View Post
My tires are rated 2540# each single. My axles are 4400# and my GVWR is 10,000# seems like I need more axle
Total 5er is 10,000#, less 20% pin is 8,000# on the axles. axles are rated for 8,800# total, tires 10,160#, I don't see the issue.

My tires on my 5er have a total capacity of 12,168# on a 12,360# GVWR. 12,360# - 20% = 9,888 so plenty of tire capacity on LT's.
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Old 12-20-2017, 11:25 AM   #11
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Quote:
Originally Posted by IRV2 View Post
My tires are rated 2540# each single. My axles are 4400# and my GVWR is 10,000# seems like I need more axle
If you deduct the trailer manufacturer's recommended tongue/hitch weight from the trailer's GVWR you will have the weight the axles are required to carry.

I found these specs for your trailer;

GVWR: 9940
Hitch: 1390

This is how the standard is written;

"The sum of the GAWRs of all axles on the vehicle plus the vehicle manufacturer's recommended tongue weight must not be less than the GVWR."

REF: FMVSS 571.120 paragraph S10.2
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Old 12-20-2017, 12:18 PM   #12
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Quote:
Originally Posted by CWtheMan View Post
Keystone has always been better with fitments for triple axle trailers. There is probably money involved with your trailer's axle, wheel & tire fitments. Those ST tires are much less expensive than the 16" LRG RST tires or the 17.5" tires used for such fitments before the strictly Asian 16" LRG tires hit the market.

Does your trailer's certification label list your axles as 7000# GAWR? Just curious. Usually RV trailer builders do not want to invite consumers to overload the trailer's GVWR.
Yes, they are listed as 7K axles on cert. I also quizzed them about the fact I had a 19K GVWR with 21K axles and 24.4K on tires. What the keystone rep, not salesman, told me was as long as I didn't exceed the axle rating on overall weight I was good to go, but...if for some reason I was weighed and I was over the 19K then sorry about my luck! With everything I'll load including both bikes I can stay around 20.5K so I'm going to say I'm good with that, maybe not for weight police but for my equipment.
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Old 12-23-2017, 01:27 PM   #13
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Geo Star 574 G. 14 ply, G rated .. load capacity 3750 at 110 psi. Been on my fifth wheel for 3 seasons of use. Very good LT tire for heavier fifth wheels. It works and gets the job done.


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Old 12-23-2017, 02:11 PM   #14
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Originally Posted by ChuckS View Post
Geo Star 574 G. 14 ply, G rated .. load capacity 3750 at 110 psi. Been on my fifth wheel for 3 seasons of use. Very good LT tire for heavier fifth wheels. It works and gets the job done.


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I don't have an older reference for Geostar but I'm pretty sure their G574 LRG LT tire was a RST - regional service trailer - tire. (A sort of GY G614 knock-off)

The newer G574s are now ST tires with more load capacity.
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Old 12-23-2017, 03:54 PM   #15
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Originally Posted by CWtheMan View Post
I don't have an older reference for Geostar but I'm pretty sure their G574 LRG LT tire was a RST - regional service trailer - tire. (A sort of GY G614 knock-off)

The newer G574s are now ST tires with more load capacity.


I believe your right. I’ve been very pleased with these as the cost is quite a bit less than G614s. I tow at 62 and after third season I’m hoping for maybe two more seasons of use. Tires are covered all the time to minimize UV degradation


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Old 12-23-2017, 04:22 PM   #16
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Not to change the topic, but for those who haven't yet changed out the air in their tires, summer air has expired and it's time to prevent problems. Winter air is free at almost every compressor, so don't wind up like this, change your air soon !!!!!
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Old 12-23-2017, 04:38 PM   #17
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Not to change the topic, but for those who haven't yet changed out the air in their tires, summer air has expired and it's time to prevent problems. Winter air is free at almost every compressor, so don't wind up like this, change your air soon !!!!!

Wow! What a timely reminder! I just did that today. Took me a couple of hours to deflate all the tires and get fresh winter air into the compressor but got er done. Thanks John.
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Old 04-05-2018, 06:40 PM   #18
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RVIA Recommendations

This has nothing to do with official regulatory standards. It is a huge organization making a stance for more reserve load capacity provisions for original tire fitments to RV trailers.

https://www.moderntiredealer.com/art...adial-st-tires
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Old 04-10-2018, 07:38 PM   #19
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Steel Cased Carlisle Trailer Tires

About 15 years ago Goodyear introduced a - what I call - hybrid 16" trailer tire known as the G614. It had a LT prefix and was dubbed RST for Regional Service Trailer. It had/has a maximum load capacity of 3750# @ 110 PSI.

Not long after the G614 became a very successful replacement tire, the "off shore" tire manufacturer's jumped on-board and started building their brand that mimicked the G614.

With RV trailers getting larger & larger the "off shore" people developed newer ST designs with load capacities suited for the 7000# & 8000# axles on the largest RV trailers.

Not to be outdone, Carlisle has now introduced their 16" LRG all steel tire line-up with the two most popular sizes.

https://www.carlislebrandtires.com/o...-detail/csl-16

I'm not plugging the brand, I have never used Carlisle tires on my RV trailer. However, Carlisle is popular with many on this forum so I've posted their info in the reference above.

Looking back, you'll find that Carlisle was one of the first trailer tire builders that foresaw the need for more load capacity for the 6500# - 7000# axles and developed 16" LRE & LRF ST tire sizes to meet the needs. Their ST235/85R16E has a load capacity of 3640# @ 80 PSI and the same tire in a LRF has a 3960# load capacity @ 95 PSI.

For a long time Carlisle recommended a speed limit of 60 MPH for their trailer tire line-up. Today, all of their Radial trailer tires are rated at 75 MPH or higher.
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Old 04-12-2018, 07:52 AM   #20
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Greenball 15" ASC trailer tire.

Greenball has added a 15" steel cased trailer tire to it's line-up. See the reference below.

http://www.greenball.com/catalog/All...nstruction.pdf
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