Fifth wheel trailer tires

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weebl

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This is about the only realm of the tire world that has me pulling out my hair. Every other application seems to have plenty of flavours to choose from, but with trailer tires, not so much.

The trailer in question, if anyone here is familiar with, is a 2010 Keystone Cougar 322QBS. It has the original factory installed tires, very little use as evidenced by the almost non-existent tread wear. And of course, DOT date codes from late 2009, putting these tires at overdue for replacement.

And that's where the problem for me is. What are some viable replacement options?

First, trailer specs:

Dual axle, with GAWR of 5,200 lbs per axle
GVWR of 11,860 lbs
OEM Tires: Power King Towmax STR II, ST235/80R16, Load Range E (3,520 lbs @ 80 psi)
Tire placard: 235/80R16E

I can already say what I DON'T want to go with as replacements:

- Power King Towmax STR II (or any other rebrand of this) - this tire has attained infamy and earned the nickname of "China Bombs".
- Goodyear Marathon - another infamous trailer tire, lovingly known as "Marabombs"

Here are some maybes, and possible issues as I see it with them:

- Sailun S637ST in either ST235/80R16 or ST235/85R16: Surprisingly, this Chinese brand seems to have earned a good reputation in the trailer world. They seem to be overbuilt, and tire weight is much heavier than others on the market. Other tires in the S637 line are truck tires, but there are rumours (no way of knowing what the truth is) these two sizes were marked "ST" simply to be classified into a lower import tax class. These tires require 110 psi to achieve max load capacity of 4,080 lbs. Could this be an issue with the OEM rims?

- Maxxis ST Radial M8008 in ST235/80R16 LRE: A Thai company (but who knows where the tire is made), seems to be a direct replacement, rated 3,420 lbs at 80 psi. Another tire that seems to have earned a good reputation in the trailer world.

- Carlisle Radial Trail HD in ST235/80R16 LRE or ST235/85R16 LRE: My personal confidence in Carlisle isn't as high, as I recall them not fairing to well when I previously researched a much smaller trailer tire, but these also seem to have a good reputation. The 80s have a capacity of 3,520 lbs at 80PSI, and the 85s a capacity of 3,960 lbs at 80 psi.

- GT Radial Maxmiler ST in ST235/80R16 or ST235/85R16: Don't know much about this tire, but GT Radial is actually Giti from Singapore, and seems to have a presence in Canada in the cheap tire market, but not so much so in the US. Appears to be well received here for their passenger car/light truck tires. Not sure if this is one I would take a chance on, without knowing much about them. The 80s have a capacity of 3,520 lbs at 80PSI, and the 85s a capacity of 3,640 lbs at 80 psi.

- Possibly consider Kenda or Duro, they seem a bit better than others, based again on my past research of smaller sizes, and also presence in other tire markets

These are all ST offerings, and so aren't my ideal, as I would really rather move to LT.

But moving to LT, while staying as close as possible to the OEM size in 16", seems to yield at best just shy of 3,100 lbs capacity.

Am I confined realistically to the ST choices? If so, which are reasonable options?
 
A 245 should clear, not sure about a 265, I won't be able to see the trailer until later this weekend. I haven't been able to find a 245 that is around 3,500 lbs, though. Am I safe at around 3,000 to 3,100 lbs, given the trailer's specs?
 
if the axles are rated at 5200lb it seems like
even derated 3100 would be enough?
 
Hmm, thinking out loud here, if these are 5,200 lb axles, then from a purely technical standpoint, it would stand to reason that a 3,100 lb tire would suffice. Mathematically, from the GVWR of 11,860 lbs, again, it works.

BUT, and it is a big but, are there LEGAL implications here? The tire placard states 235/80R16 E. This implies that at a minimum, we need to meet the Load Range E rating for that size, and going outside of that could be an issue. It translates to 3,420 or 3,520 lbs, depending on which tire you are looking at (but the placard doesn't explicitly state the rating). From that perspective, the LTs at around 3,100 lbs are out.

Would love to hear CapriRacer's thoughts on this.

Also, as Jarlaxle looks like he has gone done the same road as I have many times with trailer tires, I would love to know your thoughts on Maxxis, Carlisle, and even the Sailun tires, as realistically, those seem like the options to consider. I do really like the higher capacity of Carlisle's ST235/85R16 LRF (3,960 lbs), and that it is only required to be inflated to 80 psi and seems to be speed limited to 75 mph. And the Sailuns can handle 4,080 lbs, but at 110 psi, which I am not sure that the rims are rated for that. I don't like to be towing right at the limits of these tires, whether it is weight or speed, and would rather they be rated for much more than what I will ask of them.

And we haven't even looked at what local availability of these tires are, yet...

Can't believe this segment of the tire industry is in such a sorry state.
 
Lots of guys put LT tires in place of the ST tires. You should be able to find one to fit.

When the WestLakes go on our current trailer I'm going to try the Carlisle's.
 
Because I have 15" rims, I am leaning toward the Carlisle HD's next time. Had 1 set of Towmax STR's replaced on warranty at about 4,000 miles.
 
I have the maxxis 8008 tires on my 23ft tt. Its my second set. I have never had a problem , they aged out before worn out. Mine are 13 inch so no LT tire choices. I check the pressure before every trip.

I would run LT if they were available in my size. The Maxxis have been great. I have mine balanced.
 
Last edited:
First, ST tires and LT tires are rated for weight in different ways. ST tires are speed limited to 65 mph, and LT tires are not - which means if operated under the same conditions, LT tires should be rated at the same load.

HOWEVER, it might be difficult to convince a tire dealer to make this kind of swap. He may not understand as well as I do about how these things work and it's his business that is in legal liability.

So let's look at the math: The GAWR is 5200 pounds with a GVWR of 11,860#. It looks like the tongue weight is ~12%.

So I was going to say the tire was rated for 3420# at 80 psi, but it's obvious that Power King is doing some fancy footwork with their tire so it can be used with 7000# axles - and I personally don't like it. The Tire and Rim Association says an ST235/80R16 LR E is rated at 3420# at 80 psi - and I'm going with that.

Nevertheless, if I assume there is side to side and front to rear weight variation (and there always is!) and I use a incredibly conservative figure of 15% (or a more reasonable 10% value) - and I take into account that I think no tire should be specified more than 85% of its rated capacity, then we have a situation where a 2907# tire is being used in a 2990# situation (or a more reasonable 2860#).

So it looks like Keystone has actually done a reasonable job of sizing the tire on this vehicle.

But since you are asking, I'd recommend you go with an LT235/85R16 LR E inflated to 80 psi (which is up a size). Go with a major brand to take advantage of their technology.

I don't think you will have any trouble getting a tire dealer to do this as an LT235/85R16 LR E is rated for 3042# which is over the GAWR - BUT - they just might balk at replacing an ST as listed on the vehicle tire placard. If they do, you can either find another dealer, or bring them tire and wheel assemblies and not the vehicle.

And don't forget, this still means you have a 65 mph speed limitation.
 
Originally Posted By: CapriRacer

And don't forget, this still means you have a 65 mph speed limitation.



Even with the LT's you are limited to 65? I thought that was just the ST limit. I didn't know that.
 
Originally Posted By: spasm3
Originally Posted By: CapriRacer

And don't forget, this still means you have a 65 mph speed limitation.



Even with the LT's you are limited to 65? I thought that was just the ST limit. I didn't know that.


Opps!! I made a mistake!! Because the recommendation is to go up a size, the speed limitation is also raised - to 75 mph. (Please note: That I can not change the post where I made the mistake, so this post will have to serve as the correction!)

But, Yes! There is still a speed limitation - because we haven't established for sure that the load limits won't be exceeded. Had this been a car or a truck where we are replacing the tires with the same size, we wouldn't have to worry about this. But trailer manufacturers haven't always done their homework and given enough load carrying capacity to their tire selection, we have to be sure to be aware that we either eliminate the restriction or comply with it.
 
Thanks, CapriRacer. Looking at a photo of the placard, all it says is 235/80R16 E. Nothing else. So we would still be complying with the placard, or exceeding the placard minimum by going to an LT235/85R16 LRE.
 
Originally Posted By: CapriRacer

Opps!! I made a mistake!! Because the recommendation is to go up a size, the speed limitation is also raised - to 75 mph. (Please note: That I can not change the post where I made the mistake, so this post will have to serve as the correction!)


Speed limitation has nothing to do with tire size. It's all the tire manufacturers and how they rate the tires. The WestLakes on our camper say right on them they are rated to 75. The Carlisle's linked in the post are rated to 80-something in all sizes.

Now whether or not someone is comfortable towing at those speeds is up to them.

But the answer to speed limits is not 60 or 65, it's "WHAT DOES THE TIRE YOU ARE USING SAY".
 
I'd go LT if at all possible. I put LTs on my Cougar fifth wheel in 2009. I have much more confidence in LTs than STs.

Mine are U.S. made BFG commercial T/A
 
Originally Posted By: itguy08
Originally Posted By: CapriRacer

Opps!! I made a mistake!! Because the recommendation is to go up a size, the speed limitation is also raised - to 75 mph. (Please note: That I can not change the post where I made the mistake, so this post will have to serve as the correction!)


Speed limitation has nothing to do with tire size. It's all the tire manufacturers and how they rate the tires. The WestLakes on our camper say right on them they are rated to 75. The Carlisle's linked in the post are rated to 80-something in all sizes. .......


In this case the speed restriction is because of the loading - and because I recommended an increase in size - and therefore reduced the relative loading on the tire - the speed restriction increased.

Please note that this business of speed being related to load is an odd quirk about tires that is not normally encountered. And one that is only loosely tied to the speed rating system.

Yes, it's complicated! And the only reason this comes up here is because the trailer manufacturers haven't always done a good job of sizing their tires. This is not to say that some of the fault doesn't lie with the ST tire manufacturers, but it isn't 100%.
 
So I got a look at the wheels the tires are on. I don't remember exactly but seems the wheels are stamped with a load limit of around 3,100 lbs. which seems to bring us right to where LT235/85R16 Load Range E are.
 
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