LT-rated tires on a 5th wheel

We recently returned from a trip from Ontario, Canada to Naples. Florida. We have a Laredo 29RK (32ft), with a 2003 F350 dually TV. A trailer tire disintegrated in Georgia, doing some relatively minor damage to the underbody under the slideout. The tires originally on the trailer were Carlisle USA Trail, 225/75-15, load range D, rated at 2540lbs per tire at 65psi. These tires have always run warm, especially on the slideout side of the trailer. The weight on the wheels is 9060lbs. The weight on the pin is 1520lbs. This gives a loaded trailer weight of 10,580lbs. Listed GVWR of the trailer is 10,900lbs.

I have been meticulous about checking cold tire pressures, checking them daily while travelling. I ran 65psi in the tires. I have read in this forum, and others, about the problems many people have with Carlisle tires, and ST-rated trailer tires in general. We completed the trip to Naples using my spare, fervently hoping that a second tire would not let go, and leave me stranded at the side of the road.

After we arrived, I started to do some research to see what was available in tires. With 15 inch rims, and a 2540lbs tire rating, we were limited to ST trailer tires. I was looking for a good, American-built tire with at least that rating, but I was amazed to find that no company seems to manufacture a trailer tire in the US any more. Even the GoodYear Marathon is made in Taiwan now, after they closed the Canadian plant that made them for a couple of years. Cooper trailer tires are apparently now subcontracted to China. After reading the numerous horror stories about Chinese-made trailer tires, I was reluctant to spend $500 on a new set, and worry every trip about when the next one is going to let go.

I decided to upgrade my rims to 16 inch, and use a good commercial-grade LT-rated tire in 225/75-16 size, load range E. These are rated at 2680lbs at 80psi. There are no LT tires with adequate rating available in 15 inch. The outside diameter of the 16 inch tires is 1 inch larger than the originals, which gives 1/2 inch greater height from the center of the wheel to the outside. Clearance under the fenders was ample for the slightly larger tires. My axles are 5200lb, which have a six-lug hub and 12inch brakes, so the 16 inch wheels would bolt on. I ordered four wheels from Southwest Wheel, at $42 each. Wheels are rated at 3140lbs, 80psi. Tires were Firestone Transforce HT from the Tire Rack, at $125 each. Wheels and tires were shipped to a local tire shop in Florida.

I am running 80psi in the tires, and after a 1900 mile trip home (thankfully, uneventful), I notice a definite difference in the stability and tracking of the trailer. I usually drive at 60 - 65 mph, which is right on the speed rating for ST-rated tires, but with the higher speed rating of LT tires, I feel that there is now a comfortable safety margin. The Firestones were always cold to the touch after pulling off the interstate. I did not notice any adverse effects in low-speed tight turns, as a few people have mentioned as a possibility with LT tires.

I know one thing for sure....I will NEVER tow with trailer tires in the future. Now that all these tires are sourced offshore, it would seem that the big tire companies have now washed their hands of making a quality product. Do a search online for trailer tire problems, and there are literally thousands of people who have experienced failures, usually with the 15 inch load range D tires on heavier trailers. I really wish the trailer manufacturers would spend a couple of hundred extra dollars on a $30k trailer, and put on decent tires with a bit of reserve capacity in the load ratings. I guess a lot of buyers, especially first-time, are more interested in the colors and fabrics than what the trailer is rolling on.

Apologize for the long post, but I thought I would pass on my experiences.

Have you actually determined the correct tire pressure for the actual trailer weight using the tire manufacturers inflation charts.  If not how are you determining what pressure the tires should be inflated to?  Improperly inflated or over loaded tires will lead to tire failure.

I am not an expert, but I have been told by a couple of tire distributors that once you get to 16 inch tires there is not a trailer
designated tire. They all use an LT tire of the proper weight rating.

Dave

I couldn't find an American ST tire either. I had a blowout with a Goodyear a few years ago and I couldn't feel a change in the way it drove at all. If my wife hadn't heard it I wouldn't have stopped soon enough. After that I installed a Pressure Pro. I was really surprised at how much the pressure changes during the coarse of a day. Also having the alarm and being able to check pressure as you drive is nice.

I've thought of getting LT tires the next time, it seems there are a lot of opinions about that.

Based on the last time I weighed the trailer, loaded and ready to travel with water in the tanks, the wheel weights were 2410 lbs per wheel on the slideout side, and 2120 lbs on the other side. According to the manufacturer's load/inflation tables, I should be running 77 psi on the slideout side, and 71 psi on the other side. I am running 80 psi and 75 psi respectively, to allow for a little weight gain since the last time I weighed. I believe it is better to be SLIGHTLY overinflated rather than underinflated. I understand that the downside to overinflation of LT tires, ***as long as the maximum inflation pressure is not exceeded***, is a harder ride and somewhat more rapid wear in the center of the tread.

It is unfortunate that my trailer is not balanced side-to-side (I don't think many are). The extra weight on the slide side is caused by the slideout structure, furniture, the refrigerator and water heater. These things cannot be easily relocated. I attempt to load cargo on the light side, but the cargo area is below the hitch, so will have little effect on wheel weights.

ST-rated tires are available in 16 inch sizes. The most popular seems to be 235/80-16, which is used by many trailer manufacturers on their larger trailers (11,000 - 13,000 GVWR). GoodYear, Carlisle and the others all have ST tires in this size, but as mentioned in my original post, they seem to all be made in China now.

I have had about the same experiences as you with the 15inch st tires.  My trailer loaded is 8400lbs on the axles and around 2000 on the pin.  After trying many different brands (all made in China or Mexico now) I have come back to a carsile from load range D to load range E (2680lbs at max pressure).  These were purchased this past summer after failure of 3 Denman tires.  My next step, if the E's don't work , will be to do as you did and go to a 16" wheel.  It would be so nice if manufactures would spend the small amount extra to make a product that could be depended on to perform as expected.  joe

I have 18 trailer tires on the road at this time and have Goodyear and Carlile and have never had a failure, some run at and often just over max weight, some way below max most of the time. That said I have also read about trailer tire fails all over the web ( I been lucky) and think you did the right thing and made a good choice for size rating and air pressure. I do not think a little uneven load has any real bad effects and running high pressure will never hurt you, running low sure can. For high loads like yours 80 sounds like the right pressure to me, and  E rated tires have good stiff sidewalls at 80 psi and will most definitely make your trailer more stable and better handling then 60 psi trailer tires. Good call and good towing to you.

The outside diameter of the 16 inch tires is 1 inch larger than the originals, which gives 1/2 inch greater height from the center of the wheel to the outside.

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How about the clearance between the axles?  Going 1/2" larger on each tire's radius will place the tires 1" closer together at their closest point.

ADVICE: Do NOT run different pressures on the opposite ends of an axle! Both tires on the same axle should be infaated to the pressure required for the load on the heaviest end. Unequal pressures will cause the axle to skew slightly sideways. The 5 psi difference probably isn't a big deal, but there is no reason to have it in the first place.

The choice of LT tires rather than ST is a good one, in my opinion. We thank you for taking the time to document your experience - should be useful information to others in a similar situation.

Lou Schneider said:

How about the clearance between the axles?  Going 1/2" larger on each tire's radius will place the tires 1" closer together at their closest point.

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Before the change I had about 4 inches between the tires...now I have 3 inches. Still plenty.

huronwoods said:

Based on the last time I weighed the trailer, loaded and ready to travel with water in the tanks, the wheel weights were 2410 lbs per wheel on the slideout side, and 2120 lbs on the other side. According to the manufacturer's load/inflation tables, I should be running 77 psi on the slideout side, and 71 psi on the other side. I am running 80 psi and 75 psi respectively, to allow for a little weight gain since the last time I weighed. I believe it is better to be SLIGHTLY overinflated rather than underinflated. I understand that the downside to overinflation of LT tires, ***as long as the maximum inflation pressure is not exceeded***, is a harder ride and somewhat more rapid wear in the center of the tread.

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You should not be running different tires pressures on the same axle. Fill the tires to the pressure for the highest weight on each axle.

I switched from LT load range E tires on my fifth wheel to Goodyear G614 RST tires, which are trailer tires because the LTs I was running were too close to the weight limit for me. I don't think your problem was so much the LTs  as it was the tire load range. By going to the higher load range, even with LTs you did better and have a more comfortable margin on the load limit.

The Goodyear G614 tires are load range G and were designed specifically for trailer ops.

BruceinFL said:

You should not be running different tires pressures on the same axle. Fill the tires to the pressure for the highest weight on each axle.

I switched from LT load range E tires on my fifth wheel to Goodyear G614 RST tires, which are trailer tires because the LTs I was running were too close to the weight limit for me. I don't think your problem was so much the LTs  as it was the tire load range. By going to the higher load range, even with LTs you did better and have a more comfortable margin on the load limit.

The Goodyear G614 tires are load range G and were designed specifically for trailer ops.

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These sure look like the ultimate in trailer tires, in terms of load capacity. They appear to be available only in 235/85-16, which would not fit in my application (not enough clearance).
When I eventually trade for a larger trailer (probably Montana), these are the tires I would like to run. Did you have to do anything about the stock rims to allow for the higher pressure of a load range G?

You would need to check with the manufacturer to make sure that the stock wheels are adequate for the G614 tires. But you could always work out a deal with the RV dealer to include a set of wheels and tires as part of the purchase agreement. All part of the dickering and the buyer has the advantage in this market.

Hello,
    I read your posting on the LT tires and I was about to buy the Denman's myself for our 2008 Laredo 29RL.  I would love to know which tires you went with.  I bounced back and forth with going to the 16 rather than sticking with the 15.  As I said I was about to go with the 15 Denman's when I read your posting and now I am glad that I held off and did some more research.
We are about to depart on a long trip and I certainly do not want any tire trouble.
Would you mind sharing which tires you went with?  I went to the website you mentioned, Southwest Wheel and was not able to find what you were talking about.  I am from the same area you are in, Southwest Florida, and it would be a great help to know.  Thanks

Gary:

>The choice of LT tires rather than ST is a good one, in my opinion.<

Didn't we have a discussion here some time ago about the difference between LT and ST tires in that the ST has a much stiffer sidewall?  Seems that this is desirable when making a hard turn with a multi-axle trailer as the tires on the trailer scrub in this situation.  And, is not the ST more stable in a straight line for the same reason, leading to less trailer sway?

I've looked, and I can't find the thread, but this sticks in the back of my mind for some reason.

Frank.

samcin said:

Hello,
    I read your posting on the LT tires and I was about to buy the Denman's myself for our 2008 Laredo 29RL.  I would love to know which tires you went with.  I bounced back and forth with going to the 16 rather than sticking with the 15.  As I said I was about to go with the 15 Denman's when I read your posting and now I am glad that I held off and did some more research.
We are about to depart on a long trip and I certainly do not want any tire trouble.
Would you mind sharing which tires you went with?  I went to the website you mentioned, Southwest Wheel and was not able to find what you were talking about.  I am from the same area you are in, Southwest Florida, and it would be a great help to know.  Thanks

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The tires I used were Firestine Transforce HT 225-75/16 loadrange E purchased from tirerack.com for $125 each. The wheels were 16 inch 6-bolt modular wheels with a weight rating of 3040 lbs. The were purchased here http://www.southwestwheel.com/store/p-400-nw128700ms.aspx for $42.95 each.

Frank B said:

Gary:

>The choice of LT tires rather than ST is a good one, in my opinion.<

Didn't we have a discussion here some time ago about the difference between LT and ST tires in that the ST has a much stiffer sidewall?  Seems that this is desirable when making a hard turn with a multi-axle trailer as the tires on the trailer scrub in this situation.  And, is not the ST more stable in a straight line for the same reason, leading to less trailer sway?

I've looked, and I can't find the thread, but this sticks in the back of my mind for some reason.

Frank.

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I have seen some mention in previous posts alluding to differences in tread design and sidewall construction between ST and LT tires. Nothing definitive seems to have come out of these discussions. In my personal experience, after about 3000 miles of pulling the trailer with the LT's, the trailer tracks better in crosswinds and on uneven pavement surfaces, with less tendency to wander or sway. The tires which were originally on the trailer were Carlisles, and intuitively I can see that the Firestone Transforce 10-plys that I replaced them with are a more rigid tire. They just seem to be much more substantial. The difference in stability is not just a small difference, but enough that I instantly noticed it. The other concern was the "dragging" action which tandem-axle tires undergo when negotiating tight turns at low speed. I have noticed no ill effects due to the difference in tires. All tires will drag somewhat in a low-speed tight turn, and I think it makes little difference which tires they are, they will still be dragged sideways to some degree.

This is only my personal experience with this tire switch, and the reason I posted is to share this experience with others. I personally will never buy ST tires again, especially now that it is difficult or impossible to find a domestic-built ST tire. I feel MUCH more confident now, instead of holding my breath waiting for the next tread separation to occur.

I would like to quote this guy, he is a sharp cookie.

"I have 18 trailer tires on the road at this time and have Goodyear and Carlile and have never had a failure, some run at and often just over max weight, some way below max most of the time. That said I have also read about trailer tire fails all over the web ( I been lucky) and think you did the right thing and made a good choice for size rating and air pressure. I do not think a little uneven load has any real bad effects and running high pressure will never hurt you, running low sure can. For high loads like yours 80 sounds like the right pressure to me, and  E rated tires have good stiff sidewalls at 80 psi and will most definitely make your trailer more stable and better handling then 60 psi trailer tires. Good call and good towing to you."

Didn't we have a discussion here some time ago about the difference between LT and ST tires in that the ST has a much stiffer sidewall?

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I think perhaps you misremember the discussion, Frank. LT tires have relatively stiff sidewalls. It is P (passenger) tires that have a lot of flex. It is hard to generalize, though. Any given brand or model of tire may be stiffer than some other specific brand of the same size. In general, though, both ST & LT are stiffer in the sidewalls than a P series tire of the same size. An ST may be stiffer than a corresponding LT, but both are plenty stiff. Trailer tires don't steer like the front end of a car needs to, but they are subject to a lot of side stress when the trailer turns. Trailer tires often get dragged sideways when the tow vehicle turns, so some flex is goodness.

The bottom line is that LT tires perform very well as trailer tires and generally cost a less. There is also a larger selection of makes, models and sizes.