RV Trailer Tire Fitments

[CWtheMan]

This is a complex problem and I usually only write about such things in my tire blog. Because this problem fits so many situations with Keystone trailers I decided to address it here.

The problem starts right off with the Federal Motor Vehicle Safety Standards (FMVSS) that set the minimum values for Original Equipment (OE) tire selections for RV trailer axles. The most damaging one is the tire load capacity. FMVSS says the trailer manufacturer MUST select tires that equal or exceed the trailer’s GAWR (s). During the trailer’s certification process the trailer manufacturer is allowed to set the trailer’s GAWR. Although an axle may have a certified - from it’s manufacturer - load capacity of 5200# the trailer manufacturer can use that axle and de-rate it’s actual load capacity to 5080# for GAWR purposes. Then, following the FMVSS tire selection rules, tires rated at 2540# can be used on that axle. A popular axle size for heavier trailers is 6000#. Once there were numerous ST tires that had a maximum load capacity of 3000# that Keystone used on those axles. The failure rate for those tires was so high most of the ST tire manufacturers quit building them. So, for years 2004 & 2005 Keystone used LT tires rated at 3042# on those axles. The results were a mirror image of the 3000# ST tires. Keystone then went to the 3420# tire.

So what’s the problem? Numerous! The ST tires are a design of their own. They react differently because of their design. The sooner an owner recognizes that the better he/she will be equipped to stay within the ST tire’s operating parameters.

ST tires will de-grade as much as 10% per year. Lets say we’re very good ST tire maintainers and only suffer 5% de-grading per year. Our tires when properly serviced provide 3000# of load capacity. Within the first six months they cannot provide enough load capacity to support a fully loaded 6000# axle. Crank in a little under inflation (1.3% loss of load capacity for every psi loss) and our tires are in peril. Then there is the speed factor. Once the tires get down to the point where that cannot provide the necessary load capacity for he speed they are traveling they de-grade even more rapidly.

Bottom line: When the OE tires cannot provide at least 10% of load capacity reserves above GVWR they cannot be expected to last more than a year or two. Even at 10% they may be aged out in three years.

Durability does not seem to be a factor for ST tires manufacturers to concern themselves with. Durability does not add tire strength but it can increase it’s life span.

CW

[Ken / Claudia]

That is sad that some trailers do not have any or little reserve wt. left in the tires. I just checked my trailer and tires. Trailer scaled wt. loaded with full fresh water and camping equipment including the tongue is 6600 lbs. Each tire is rated at max wt. 2540 lbs. In my case I have a light weight trailer compared to many. Seems I have reserve wt. left in the OE tires to last a few years. The date code is 2011 so I may not have many years left.

[buzzcop63]

Ken has the 2013 model of 24RKSWE and I have the 2012. My scale weight while attached to my truck is 5,500 Lb; this is with both axels on the scale, all tanks empty, maybe 4 gal fresh and trip loaded. If my math is correct weight on each tire is 1,375Lb with max weight for my OEM tires at 2,540Lb would be using 54% of the tires carrying ability with the same date code as Ken. Note the same tire is used on the next larger model with greater weight trailer and less margin of safety.

[JRTJH]

It's the same with our Cougar with a GVW of 10k. It came equipped with ST225/75R15 LRD Towmax tires rated at 2540 each @65PSI. That's 10160 total on the axles which are rated at 4400 each, with the "shipping pin weight" of 1140.

When loaded for a trip, the pin weighs 1800 lbs and the total trailer (uncoupled from the truck) weighs 8650. That would put 6850 on the axles.

I'm no tire expert, but it looks like about a 32% "margin of safety" if you take the pin weight out of the picture and a 15% margin if you consider the entire trailer weight.

On the other hand, our Springdale was significantly different. It had a GVW of 8105, a pin weight of 1105 with 3500 pound axles and 205/75R15 LRC tires rated at 1820 each. Loaded for trips, we had a total trailer weight of 7500 with a pin weight of 1450. That put 6050 on the axles.

So without the pin weight, the margin was 18% and if you consider the entire trailer weight, the margin was overweight at 103%.

I make these comparisons to show how even within Keystone, some trailer models have significantly more "tire weight capability" than others. Both of my trailers "meet or exceed" the minimum requirements, but in my case, the Cougar has a much larger margin of safety than did the lighter Springdale.

[GmaPaTime]

John... Thank you for the axle/tire weight safety level breakdown from your trailer weights. I've been wanting to do this but haven't gotten around to it.

Since our trailers are very similar in weights, my stated pin weight is heaver but the 10k GVW and loaded weight being just shy of 9k are the almost the same, results would still be in the 25-30% range.
In your opinion, do you think that with leaser safety margins on other trailers because of the heaver weights could be the cause of so many blowout issues of the Towmax brand tires?

[CWtheMan]

I wasn’t talking about Keystone in the past. They still fudge on tires on 2014 models.

The 2014 Bullet TT model 285RLS has a shipping weight of 5480# with a cargo capacity of 2105# giving it a GVWR of 7585#. Deduct the published hitch weight of 585# and the weight on the axles is 7000#. So that’s two axles at 3500# GAWR. The specs say that trailer’s OE tires are ST205/75R14C. Those tires are rated at 1760# at 50 psi for a total of 3520# of load capacity on 3500# axles.

There are many more, especially up in the 6750# GAWR area.

The shipping weight is determined after final vehicle certification. Anything (options) added by the dealer over 100# requires them to adjust the trailer’s cargo label. It is mandatory for the trailer manufacturer to establish and publish a hitch weight. One of the regulations requires them to insure the published hitch weight when added to the total GAWR equals or exceeds GVWR.

CW

[JRTJH]

Steve,

I'm sure that running tires at (or very near) their maximum weight ratings is a factor in tire reliability. I think that many of us (who knows the real number) hardly ever stay at or below all the design limitations with our tires. There's the weight limit, pressure limit, speed limit, not to mention maintenance items such as balancing, side stress in backing, bruising from potholes and curbs, putting the wrong dressing on them (so they look good) coupled with UV protection (or lack of it).

Tires are one of the most "abused" components on most RV's, so I think that for the most part, IMHO, the trailers with less "safety margin" in weight vs tire capacity is probably a big factor in tire reliability. I don't think it's only "the heavier trailers".... In my own experience, my "lighter Springdale" had significantly less "safety margin" built in than my heavier Cougar.

What concerns me (and I'm not trying to start a "fear factor") is the "light-weight" trailers that are pushing 30+ feet in length and are running on wide spaced axles with 14" tires. Just the stress of backing with axles that far apart coupled with the smaller tires and lighter capacities is concerning. But, it seems (from what I read) that there's less damage from blowouts on those trailers than on the heavier ones, so who knows? The data are hard to find on ST tire reliability, and I wonder if LT tire reliability when used on an RV is reported as accurately as is the LT tire reliability when used on trucks????

[Ken / Claudia]

This is a good post, it explains a lot. I ask yourself to think about the new trailer and tires. Just sitting on the flat ground, we check weight by axle, normally. Each tire could have more or less wt. than the total divided by 4. When driven on a grade weight shifts, weight shifts on cornering and braking. And all that can change just to the weight put on each tire as being driven. Throw in age, under pressure conditions, unknown tire damage just from driving. When it started as new and not much reserve left, it is no wonder to me why so many rv tires fail. Is China to blame or the trailer builder or the Feds using their standards outlined by CW.

[Festus2]

Originally Posted by Ken / Claudia

Is China to blame or the trailer builder or the Feds using their standards outlined by CW.

Ken:
I'm not sure if we can blame "China" the country for tire problems but the tire manufacturing plants in China might contribute to the problem. So who, besides these tire plants, might be a player in the "blame game"?

Let's look at Keystone to see what part they could play. The folks there decide what tires they are going to put on their RV's. They could, if they wanted to, put on a higher quality tire but for obvious economic (aka profit) reasons they chose not to. Instead, it appears that they put on tires, often referred to as "Chinese Bombs", that meet the minimum requirements.

Now, what about the owners? It is our responsibility to take care of whatever tires are on the RV - Chinese or not. Is it partly our fault for towing an RV whose tires are underinflated or too old? Driving too fast? An overloaded RV? Perhaps we (except any forum members) are guilty and have to accept some of the "blame".

And finally the regulators - those people who set the standards and who are supposed to make sure that those tires are "safe". What part do they play? Are they somehow manipulating the numbers to a point where they have become almost meaningless? Are these tires being thoroughly tested to ensure that they are in fact "safe"?

I don't think you can point fingers at any one group. There's enough "blame" to go around.

[Idahoguy]

Well put Sir...Have dealt with heavy truck and light truck tires most my adult life...First get quality tires, proper alignment of axles, proper tire pressure, proper trailer weight and distribution and last proper maintenance. It does not have to eat in to manufacturers profit. Just charge me more when i buy the trailer and tell me that I have a top quality trailer with the highest quality tires with properly aligned axles. They have NO excuses for the biggest safety factor on a trailer. Other than proper brakes and driver. The last items are another discussion. lol

[fla-gypsy]

I have built in about 15% reserve capacity on my TT by making good choices in tires and thanks to Keystone placing axles on my TT that exceed the stated GVWR on the trailer. I understand this is not the norm and this is a real issue for many TT owners.

[cathcartww]

There have been some very good points made in this thread, but I still think the quality of the average ST tires available leaves a lot to be desired. Choices of "premium" quality tires are very limited.

We purchased our 2012 (built late 2011) Outback 277RL used in Spring, 2011. It grosses 8600 with a tongue weight close to 1000 lbs. It came with 4400 lb axles and 225/75R15 LR D "Road Rider" tires manufactured in October, 2010, which should have plenty of "reserve capacity" I am almost anal about the tires - keep them covered when not in use, use a TPMS, mechanically check the pressure before each day's use, carefully inspect them before each trip, and scan through the pressure/temperatures and give them a look-see and touch test at each stop during the trip. We cruise just under 65 mph because that is the "sweet spot" the van likes to run at. They have about 12,000 miles on them, with nice even tire wear and are showing like 70% of tread. I was planning on replacing them this spring, since they will have their 5th birthday this year.

On the way down to Florida, on I-95 near Stuart, FL, about 100 miles from the last stop, the left rear tire blew out. There was no indication of temperature increase or pressure loss, just catastrophic failure. We felt it go, and were able to pull off within a tenth of a mile or so, but by then, the tread was gone, and the tires shredded. Luckily, there was no damage to the trailer.

Make a long story short, the Maxxis LR E's (yes, the wheels are rated for 80 psi) that we had planned to have put on in the spring, had to be purchase a little sooner, but at a higher cost, and mucho inconvenience. Inspection of the old tires did not reveal any obvious problems other than one seemed a little "out of round" at least to the naked eye. Road damage is of course possible, but you would think the LR would be the least like to pick up something to cause catastrophic failure.

I hope the Maxxis give me better service, but wish I had more options

[theeyres]

I still put 90% of the blame on Keystone and all the other manufacturers. They are the ones that decide what goes on the trailer. I know I can load my truck down, like I just did, with a load of gravel until the tail is almost dragging the ground, go slow and make it home without the tires blowing. I would never attempt that with my trailer as I know all the specs are absolute minimum. I also know I have had various TT for the last 40 years and tires were never a concern until recently. I could run them almost bald with no fear. But something has changed...and I can't help but think it is the manufacturer's going cheaper and cheaper.

I think it is totally unfair to expect the buyer's to somehow research tires before buying and somehow figure out that they should dump the cheapo trailer tires and immediately upgrade.

Nor is China to blame. They make what we ask them to make.

[NotyetMHCowner]

I don't get it either. Would I not buy my camper when the price goes from $50,700 to $51,700 because they put quality tires on it? HECK NO! I am tired of hearing about the cost when we are talking about rigs in excess of $30,000. I just refuse to believe someone would not buy a particular unit because the price went up $1000. It doesn't make sense to me.

I have also said there are three things that need to be taken care of and are of the upmost importance: Tires, Bearings, and Brakes. The fridge can quit, the furnace let go, slide stop working, etc. But at least I can get it home!

[Ken / Claudia]

Post #14, you get 5 stars for what you said.

[Todd727]

Originally Posted by NotyetMHCowner

I don't get it either. Would I not buy my camper when the price goes from $50,700 to $51,700 because they put quality tires on it? HECK NO! I am tired of hearing about the cost when we are talking about rigs in excess of $30,000. I just refuse to believe someone would not buy a particular unit because the price went up $1000. It doesn't make sense to me.

I have also said there are three things that need to be taken care of and are of the upmost importance: Tires, Bearings, and Brakes. The fridge can quit, the furnace let go, slide stop working, etc. But at least I can get it home!

Well, there are many posts of guys trying to find the best deal on tires and they go for ST. They spend 30-80K for a unit and then cringe at the thought of putting a set of G614 tires on. Having watched a guy speed past me and then having to drive through his debris trail as a blown tire shredded the side of his 5'er, I just have to shake my head. I bet $1500 worth of real tires would've been chump change compared to the expense and hassle he incurred that day.