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  • Writer's pictureBill Lindemulder

Everything You Wanted to Know About Trailer Tires (and a lot that you didn't)!

Updated: Jun 22, 2023

We started selling and installing trailer tires at Wild Mountain RV shortly after we first opened. We wanted to offer our customers a ‘one stop’ solution for their trailer maintenance and realized that a huge headache for trailer owners was having to take their trailers to a tire shop for new tires. The headache was due to not being able to leave their trailer with the shop, waiting for the new tires, trying to find parking, etc, etc. Here at our shop, you can drop off your trailer and have the tire changed while you are getting other repair work done, during regular maintenance, or just for the tires. We also discovered that there is a lot of information that trailer owners do not know about trailer tires; information we didn’t know at first either, and information that most RV repair shops and dealers who do not sell tires will also not be aware of. So, here is the information that we find we share the most to our customers concerning trailer tires. **note** the information here is only for trailer tires and not for motorhomes, as those questions are still best left to the motorized vehicle tire experts.

  1. When do I need new tires? This is a common question, and the answer might surprise you. To start with there are a couple of obvious answers, and then one not widely known:

    1. When your tires have no more tread left. This is not very common as trailers are not used nearly as much as vehicles, and tires will almost always “age out” before they go bald. If you have uneven wear, or balding on your tires, this is the result of other issues which I will explain further below.

    2. When there are cracks in the tires. Sidewall cracks are most easy to see, but sometimes trailer tires will develop cracks in-between the treads of the tires as well. Take the time to really inspect your tires regularly for cracks. The cracks will usually appear on tires that were ‘south facing’ during the winter months. If you store your trailer with any part of your trailer tires facing south, make sure to cover them – preferable with tire covers – to prevent this UV damage.

    3. After 7 years. This is the one that most trailer owners do not know. This rule is not widely known because most of us only have dealt with vehicle tires. Did you know that all vehicle tires should be changed every 6 years regardless of mileage? We don’t know this because most vehicle tires are changed every 3-5 years as they wear. You will often find this same 6-year rule for trailer tires, but at Wild Mountain RV we recommend 7 years, as using this measurement usually means the tires have been used for 6 seasons. How do you know if your tire are 7 years old? Is the 7-year rule based on the date of the tire or the date installed? Here are those answers:

      1. How to find the manufacture date of your tire? You can find your tire date on the side wall by finding the ‘DOT code’. The DOT code is usually 8-13 letters and numbers preceded by the letter ‘DOT’. You don’t have to know what the letters all mean, just the last 2 numbers. There are usually 4 numbers at the end of the DOT code, indicating the week and year the tire was manufactured. So, the last 2 numbers will show you the year. If you can’t find the DOT code on your tire, you will have to crawl under your trailer and read it from the inside sidewall. If your DOT code does not have the 4 numbers, then your tire was manufactured before the year 2000 and you desperately need new tires!! 😊

      2. Is the 7-year rule based on the date of the tire or the date installed? Most tires are manufactured, shipped, and used quite quickly so the difference between date manufactured and installed is usually only 3-8 months apart. The more common brands and sizes will not have that big of a gap. The general rule though is to use the date installed. This is because the tire degradation occurs from being in the outside elements and sun exposure, not sitting in a warehouse. For most trailer owners they do not know or remember the installation date of their tires, so then they need to use the DOT code date.

  2. My tires look fine, even if they are past the 7-year mark. Do I still need to change them? I will never tell a customer what they ‘need’ to do – it’s your trailer, your decision. If the trailer has always been stored inside, for instance, then the life of the tire may extend past 7 years, but you need to be aware of why 7 years is the rule. Tires break down regardless of amount used, and the risk of blowout increases every year. One of my favorite stories regarding this issue involves a family member. This person brought me his new to him trailer for a long list of work. When I informed him that his tires were 12 years old, they asked what they looked like. I told him they looked fine, but that they needed to be changed. He said, “what do I care about how old the tires are?”. He picked up his trailer and called me half an hour later to inform me that AMA was changing one of his trailer tires on the side of the road and that he was bringing it back for 4 new tires.

  3. What kind of tires do trailers use?

    1. Trailer tires are usually what are called ST tires, which stands for ‘Specialty Tire’. You will find the ST at the start of the tire size – for example ST225/75R15. Some very large 5th wheels and old trailers will have LT tires. The LT stands for ‘Light Truck’. There are not a lot of differences between the two, except for 2 main design features. ST tires are designed to withstand the forces that a trailer puts on tires, namely the side-to-side torque and twisting they experience with sharp turns. They can better withstand this due to a stronger sidewall. ST tires are also engineered to limit the amount of “rolling resistance”. Better rolling resistance equals greater gas mileage. With that being said, you should still only use the recommended type of tire for your trailer. This information can be found on the ‘Trailer Tag’ on the front driver’s side of the trailer (usually with or including the VIN). When large trailers call for LT tires, it is best to stick with LT tires as the trailer was designed for these tires, and (strangely, as we found out the hard way), the diameter of the tire may be an issue between the ST and the LT tire.

    2. Radial or Diagonal Bias Tires? You probably didn't even know there was 2 types. I didn't either until I started selling tires. The difference between the 2 is the construction type of the tire. Radial tires (indicated with an "R" on the tire size - ST205/75R14) are constructed with crisscrossing steel belts running from bead to bead straight across the width of the tire. Diagonal Bias tires (indicated with a "D" - ST205/75D14) are constructed with crisscrossing cords of polyester and nylon at 30 to 45 degrees of the centerline. You can look up the difference online for details of why Radial tires are better, but generally they are better because they are stronger and last longer. Manufacturers were using Diagonal Bias tires for a few years because they were cheaper. I have not seen these on new trailers for few years now, which tells us that even the manufacturers realized they were inferior.

  4. What is ‘Load Range’? On trailer tires you will also find a ‘Load Range’ written on the side wall, as well as indicated on your Trailer Tag (right behind the tire size). Trailer tires are most often Load Range ‘C’, ‘D’, or ‘E’ for the very heavy trailers. The load range is exactly what it indicates, how much load (in pounds or kilos) a tire can handle. This used to be referred to by the number of 'Plys' a tire had (an 8 ply tire, a 10 ply tire, etc). Although the term 'ply' is still used sometimes, it has been replaced with 'Load Range', due to the fact that tire manufacturing has changed and no longer has a specific number of plys. All tires have an exact load range written on the side wall, but the letter category is all you need to know. When buying new tires, you can always use the recommended load range, or go one size up (if it is available), but you should never go down. For example, if your trailer has load range ‘C’, you can go to ‘D’ if you wish, or if those tires are what is available. Because the price is not much different, I usually recommend going up if that is an option as the heavier load range will have a stiffer sidewall. With that being said, going up in load range does not mean your trailer can now carry heavier weight. The entire suspension is designed for the max weight indicated on your Trailer Tag. Your axles, suspension system, and tires were all designed to not exceed a certain weight and you must stick to this.

  5. What brand of tire is the best? Here at Wild Mountain RV, we normally offer 3 brands of tires. An ‘economy brand’, ‘middle of the road’, and a ‘top of the line’ brand. In order we sell Road Rider, Carlisle, and Goodyear. Which brand to buy really comes down to customer preference and number of kilometers put on the trailer. Personally, we only use our trailer a few weekends a year and one longer summer vacation, so I always go with the economy brand for my trailer. If you put on lots of kilometers or take your trailer down the ‘trunk roads’ of Alberta often, you will want to spend the extra money and buy the top of the line. If you are somewhere in-between or unsure, go with the middle of the road. Sometimes availability becomes a factor as well.

  6. What if my tires are wearing unevenly? Uneven tire wear is the result of factors that can sometimes be difficult to diagnose. Here are some scenarios:

    1. Underinflation. An under inflated tire will have equal tire wear on the inside and outside edges of the tire. Trailer tires should always be inflated to the max PSI when cold (which means after sitting – not right after moving).

    2. Overinflation. An over inflated tire will have tire wear right down the middle of the tire. Once again, ensure tires are inflated to the max PSI when cold.

    3. Outer or inner edge of tire worn on one or multiple tires. This is usually an indication of a bent axle. Bent axles should be replaced. There are some suspension shops that will “straighten” bent axles, but once an axle bends, it is prone to bend again (this is information that I have learned from my customers over the years). The replacement axles we use at Wild Mountain RV are manufactured using the dimensions of the existing axle and are usually stronger that the original axle. The cost for replacing an axle is not quite as expensive as you may think, and in the long run will save the cost of replacing the tires every couple of years. The exception to this is torsion axles. These are almost double the price of straight beam axles and tend to have a lifespan even if they don’t get damage.

  7. Do I need to have my Trailer Tires Balanced? The short answer is "no". This is once again a customer preference, and some of our customers do ask for balancing, which we do offer as an extra service. Most new tires manufactured today are quite close to "balanced" straight from the manufacturer. The reason passenger vehicle tires are balanced is mostly for steering, and if not balanced, the passengers or driver may feel a slight vibration when riding in the vehicle. Trailers come from the manufacturer without balanced tires, and there is no reason to balance your new tires either. There is one other side of this; if a tire is very 'out of balance' it can cause your trailer to shake (vibrate) and loosen components or shift belonging. This is the reason some of our customer request balancing when purchasing new tires.

As you can see, there is a lot to know about trailer tires, and thankfully there are blogs like this to be able to share all this information as it is impossible to explain it all over the phone. If you have any further questions, please reach out and let us know!

Trailer Tires

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