How to Pick the Best Trailer Tire
We might use our trucks, SUV’s or cars every day of the week, but trailers are the real workhorses of the automotive world. Without them, our toys, work equipment and the larger of life’s necessities wouldn’t get where they need to be. But how often do we take stock of the rubber under our trailers? The answer for most people is “very seldom.” Unfortunately, the trailer tire is one of the most neglected vehicular components rolling down the highway. Some folks don’t even know there are trailer-specific tires, and even if they do many more aren’t aware that trailer tires should never be substituted with car tires.
In sourcing the perfect tire for your trailer, the tire’s design, load range, size and your trailer’s gross vehicle weight rating (GVWR) should all be taken into consideration. To help you in your quest for the right trailer tire, we’ve not only spelled out the key differences between trailer and car tires, but also how bias ply and radial trailer tires differ. In addition, we’ll go over proper air pressure and how it correlates to load carrying capacity, appropriate sizing, tread wear tips and proper tire maintenance. Your tow-rig is already your pride and joy. Let’s make it tow your trailer as effectively and safely as possible.
What Exactly Is A Trailer Tire?
First off, never put car tires on your trailer. The design of a car tire places a lot of emphasis on comfort and ride quality, which entails a more flexible side wall. The opposite is true for a trailer tire, where a rigid sidewall is what you want for max load carrying capacity and stability. Trailer-specific tires can be broken down into two groups: radial and bias ply. Both are in the special trailer (or “ST”) tire category. Many radial trailer tires feature low rolling resistance for optimum efficiency and wear protection. Load ranges for either radial or bias ply tires range from B through F.
Radial Trailer Tires
The unique makeup of a radial trailer tire entails an inner steel belt layer that runs at a 90-degree angle from the tread center line. Radials offer much less rolling resistance than their bias ply counterparts, which means they dissipate heat more effectively and as a result the tread lasts longer. Their low rolling resistance also lends itself to better fuel economy. It’s also worth noting that, unlike bias ply tires, radial trailer tires aren’t known to develop flat spots when sitting for extended periods of time. For seasonal trailers like campers and travel trailers, this is a key selling point for radials over bias ply.
Bias Ply Trailer Tires
Different in construction from that of a radial trailer tire, a bias ply tire features an inner layer of cross-hatched nylon and steel cords, which sit at a 30 to 45-degree angle from the tread center line. In general, bias ply tires have stronger side walls than radials, which promotes stability and less trailer sway. Rolling down the road, a bias ply tire’s more rigid construction tends to make them run straighter than radials. They’re also typically more affordable than the equivalent radial option.
Finding the right tire for your trailer always begins with the trailer’s gross vehicle weight rating (GVWR). GVWR includes the weight of the trailer itself, plus the maximum cargo it can carry (i.e. its “loaded” weight). For example: a 10,000-pound GVWR travel trailer that weighs 6,300-pounds empty can be loaded with 3,700 pounds worth of cargo before reaching its GVWR. In this tandem axle example, each tire would need to have (at least) a 2,500-pound load carrying capacity. To find out what your tires’ load carrying capacity minimum needs to be, simply divide the trailer’s GVWR by the total number of tires (in our example: 10,000/4 = 2,500). Luckily, trailer manufacturers almost always include tires that (when combined) exceed the trailer’s GVWR by a fair margin.
The next item to look at is your trailer’s gross axle weight rating (GAWR). The combined GAWR from each axle under your trailer will always exceed the trailer’s GVWR, but that doesn’t mean you can tow more than GVWR. Along the same line of thinking, just because you bought tires with a load carrying capacity higher than what the trailer originally came with doesn’t mean you can overload your trailer.
An additional thought on trailer tires is to always check its speed rating. Even though you might be able to get a great deal on a heavy-duty, 14-ply set of tires, the speed rating may be lower than you think. Most trailer tires’ maximum speed ratings check in at 65-mph. Running a 65-mph-rated tire 75-mph down the highway can increase its inflation pressure as much as 10-psi without the trailer seeing any increase in load. Among the numbers listed near the edge of the rim in the photo above, you’ll find an “N.” This speed rating means the tire’s maximum rated speed is 87 mph.
Load Carrying Capacity Explained
A trailer tire’s load carrying capacity should be selected based on your trailer’s GVWR and GAWR information, but instead of matching your trailer’s GVWR it pays to add a little insurance. In the photo shown above, each tire on a single-wheel, tandem axle toy hauler is rated for a maximum of 2,830 pounds. The fully loaded trailer (i.e. its GVWR) tips the scales at 9,995 pounds, but the tires—provided they’re inflated to maximum pressure—can handle 11,320 pounds in theory. Also take note that in dual wheel applications each individual tire’s carrying capacity checks in at a lower, 2,470 pounds. This is typical.
Stick With the Same Tire Size
Regardless of whether or not you choose radial or bias ply trailer tires, it’s best to stick with the trailer manufacturer’s recommended tire size. To this extent, keep the load range the same (or at least close to the original tires’ load index number, which is visible on the sidewall). Also refrain from mixing and matching different tires. Different brands, models and types may wear differently and have varying load carrying ability. Also make sure that your spare is the same size and has an identical load carrying capacity. If you need the spare and it can’t handle the same weight as the others you could wind up on the side of the road again.
How to Make Trailer Tires Last
Trailer tire longevity begins with air pressure. Always check, inflate or bleed air pressure when the tires are cold and make sure you use an accurate gauge. Once a month or before setting out on a lengthy journey, always ensure that air pressure is where it’s supposed to be. For trailer tires, this usually means running them at their maximum rated inflated pressure for utmost load carrying capacity. Just as important, keep all tires on an axle the same pressure. Under-inflation leads to poor fuel economy, hinders maximum braking potential and decreases a tire’s handling.
Rotate Every 5,000 to 6,000 Miles
Just like your car, truck or SUV, rotating your trailer tires every 5,000 to 6,000 miles will allow the tires to wear as evenly as possible. It’s also worth keeping tabs on tread wear with a tread depth gauge. In general, trailer tires should be replaced once tread depth reaches 3/32-inch. Regardless of condition, trailer tires should be replaced every six to eight years—and immediately if abnormal wear, corrosion or other damage is spotted. Keeping relatively new tires on your trailer can save you more than just the hassle of having to install your spare in the middle of a trip, it can save you from experiencing the kind of blow-out that causes fender, flooring and body damage to the trailer.
One of Your Tires' Biggest Enemies is the Sun
The life of a trailer tire is a hard one. Unlike the tread fitted to your car or truck which may spend most of its time in a garage, trailer tires are typically exposed to the elements year-round. On top of that (literally), many trailers perpetually have weight on them, such as with enclosed box trailers and travel trailers. In our experience, the most destructive force your tires face is prolonged exposure to sunlight. After extended time soaking up its UV rays, the sun dries out the oil present in the tire’s compound, leading to dry-rotting and corrosion. The best way to preserve the life of trailer tires is to get them out of the sun, be it by parking the trailer under shelter or (most affordably) shielding them with tire covers.
On the hunt for fresh tires for your tow rig? Check out the long-term test we’re conducting with Nitto’s Ridge Grappler here.