ST tires: All-steel radial construction is meeting the demand for more carrying capacity

Ann Neal
Posted on June 2, 2015

Special trailer (ST) tires are bigger, heavier and increasingly available in all-steel radial construction to meet the towing demands of more powerful vehicles and larger campers.

“With the power of today’s vehicles, it’s normal to see them towing a triple-axle trailer in the fast lane passing other cars. The strain of higher speeds for prolonged amounts of time while under constant load is much higher than what many ST tires were originally designed for. So now there is a demand for a more robust ST tire that meets today’s towing demands while still being economical in price,” says Randy Tsai, director of marketing and GBC Motorsports for Greenball Corp.

The current technology in ST tires, specifically radial ST, was developed in the 1990s when the maximum speed rating was 55 mph for ST tires. The trucks of the 1990s were lucky to get up to 55 mph when towing a trailer, says Tsai. “Today’s tow vehicles are far more advanced than ever before. Heavy-duty diesel light trucks of today have horsepower in the 400-plus range and torques that are 700-plus foot pounds or more.”

Bill Dashiell, senior vice president of TBC Corp.’s commercial division, says trailers, especially RV trailers, are getting larger and heavier and are requiring tires that will accommodate this increased load. “RV manufacturers are moving to more all-steel ST radials to better accommodate the increased loading requirements on the largest luxury models. Even more traditional ST radials are coming out with new designs to improve tire wear and reduce heat buildup.”

Dashiell says the heavy-duty ST radial tires are designed similar to an all-steel truck tire and are able to handle the high loads and provide substantial performance improvements. These tires are available in 16-inch and 17.5-inch sizes.

East Bay Tire Co. sells the Carlisle and Duro brands of ST tires. The Carlisle Radial Trail RH, which East Bay says provides improved load-carry capacity and lateral stability to reduce trailer sway, is pictured.
East Bay Tire Co. sells the Carlisle and Duro brands of ST tires. The Carlisle Radial Trail RH, which East Bay says provides improved load-carry capacity and lateral stability to reduce trailer sway, is pictured.

“While these tires provide significant load and performance improvements, the trade-off is the need for higher load capacity wheels and an increase in acquisition cost. However, for high load applications the benefit of the HD ST radial tire far outweighs any associated increase in costs,” he says.

In January 2015, TBC introduced the Sailun S637T HD trailer tire with all-steel construction available in ST metric sizing. Greenball also will introduce all-steel ST tires in 2015. “We plan on launching an ultra-premium all-steel construction ST line in 15- and 16-inch fitments as well as another line in the 17.5- and 19.5-inch fitments,” says Tsai.

Bias versus radial

American Kenda Rubber Industrial Co. Ltd., which does business as Kenda USA, is also seeing a strong move to radial tires at the OE level in more applications, according to Joe Ostrowski, sales manager for Kenda’s Americana Tire Division. “While the bias tire has its place in the market, the radial is being used as a selling feature by the OEs.”

He has a “rule of thumb” for using bias or radials. “Bias, shorter trips, rough terrain. Radial, longer trips and smooth ride. The bias tire runs more on the center crown of the tire while the radial has more road contact across the tread. This leads to the heat being dissipated across a greater area providing longer wear and smooth ride.”

Tom Van Ormer, director of purchasing for East Bay Tire Co., agrees ST tire technology has evolved, but the trick is finding tires that have it. “The ‘new’ technology is existent in the ‘name brand’ trailer tires only.”

During a visit to China in April 2015, Van Ormer saw many new lines of ST products, but says he is aware of only one manufacturer that has “truly changed” the technology of the ST tires. That manufacturer is Carlstar Group LLC, formerly CTP Transportation Products and before that, Carlisle Transportation Products. “With the RH (radial) and LH (bias) trailer tires, they beefed up the bead and sidewall packages so that few others can compete quality-wise with them,” Van Ormer says.

“We see new offers of ‘less expensive’ trailer products from multiple Chinese sources, but none of them seem to offer any new technology, only cheaper prices. These may be fine for farm and construction use, but not for over-the-road, high-speed applications the consumer uses the ST tires for today.”

The Kenda Loadstar K550 was designed specifically for trailers. The company says it has a radial tire’s appearance and a bias tire’s durability. It features longer tread wear, low rolling resistance and increased towing stability.
The Kenda Loadstar K550 was designed specifically for trailers. The company says it has a radial tire’s appearance and a bias tire’s durability. It features longer tread wear, low rolling resistance and increased towing stability.

From LRD to LRE

There are more uses for ST tires that are larger in size with increased load carrying capacities. “ST tires are specifically designed for trailer applications, and the movement into larger sizes brings the benefits of a tire specifically designed for towing to more applications,” says Ostrowski.

The wheel well space on most trailers limits how large ST tires will become. However, the demand to increase carrying capacity has been steadily growing. “One prime example would be the ST225/75R15,” says Greenball’s Tsai. “Traditionally the heaviest load range was LRD. Now most of that demand has now changed to the LRE, which in our Towmaster lineup has an increased load capacity of 290 pounds.”

There are two reasons for the increase in carrying capacity, according to Tsai. The first is trailer manufacturers, specifically the recreational travel trailer manufacturers, are building larger and more elaborate units that require more load carrying capacity. The second is the consumer perception of a heavier load capacity being more robust.

“I once had a consumer request for us to build an ST205/75R14 14 ply,” says Tsai. “I asked her what she was pulling in her trailer and why she would need such a high load capacity from a small tire. Her reply was that she didn’t carry anything heavy but a sport ATV on her trailer, but that she was constantly getting blowouts so she wanted a 14-ply ST205/75R14.”

Tsai’s example highlights the need for dealers to keep up with what is in demand for the towing market. “As consumers demand or desire an ST tire with higher load range, dealers need to be sure they have access to that tire with the proper load range the consumer is looking for. As in my example of ST225/75R15 moving from LRD to LRE in demand, there are other smaller sizes that are doing the same, such as the ST205/75R15 which traditionally has only gone as heavy as an LRC. Now the bigger demand is for the LRD.”

Consumers’ changing expectations are also affecting East Bay Tire Co., a wholesaler, exporter and commercial dealer with nine locations in California and Hawaii. “We see many more 225/75R15 10 plies and a large move to the higher ply 235/80 and 235/85R16 tires. The demand is because trailers and boats are getting bigger and equipment is being moved more and more on trailers, so they lean toward the products that can handle the heavier loads,” says Van Ormer.

Doug Addis, territory sales manager for Maxxis International, says his company does see a trend toward bigger and heavier tires. “Campers are getting larger which requires a larger tire or a heavier load range to support the added weight. Dealers will need to add the larger sizes and new load ranges to their inventory in order to address these larger campers and trailers.”

Maxxis says the STM8008 Radial is a rugged trailer radial with a robust casing design and proven durability. Its features include double steel-belted construction for added strength and increased vehicle towing stability
Maxxis says the STM8008 Radial is a rugged trailer radial with a robust casing design and proven durability. Its features include double steel-belted construction for added strength and increased vehicle towing stability

No substitutes for ST

Consumers may be tempted to swap their ST tires for LT tires. The experts who contributed to this MTD article advise against it due to potential differences in load capacity.

“The sidewall of a trailer tire is designed to support a load while being towed; an LT tire is originally designed to be used on a light truck. Overall, performance in a towing application is better served with an ST tire. Anytime an ST tire is available for a trailer it will better serve the consumer,” says Kenda’s Ostrowski.

Tsai says that as long as the size is the same, people will always assume that they can use a P or LT tire to substitute for an ST tire. “Many don’t think about or take into consideration that Ps/LTs and ST are designed significantly different from each other. Just as in the case of a P-metric versus an LT, the tires are built differently from one another. ST tires are built to carry heavy loads on non-powered axles. Your average ST tire built in the same size as a LT or P will carry a heavier load. The compound in an ST tire is also different and optimized for its application,” he says.

Maxxis does not recommend using an LT in a trailer application, according to Addis.

Sales expected to grow

Demand for trailer tires is expected to remain steady and even grow. “In general, the ST tire market has cooled down a bit from its high between 2006-2009,” says Tsai. “However, demand will always be out there and will always be steady. For 2015 we do not see any significant drop in ST tire demand, but rather an increase in supply due to the anti-dumping tariffs on PCR and LTR coming from China,” he says.

The significant growth in RV sales will benefit ST tires, according to Kenda’s Ostrowski. “Conservatively a growth of 10% to 15% should be anticipated. From a dealer perspective, I would increase my stock on radial tires. Consumers are more familiar with radial tires and will accept it readily as a replacement. It is best not to mix radial and bias tires on the same trailer,” he says.

The outlook for the ST market is favorable at TBC, as well. “2015 should be a good year for trailer tires. The economy continues to improve leading to increased disposable income. One of the results is the increase in RV sales,” says Dashiell.

Trailer tire sales have steadily increased over the past several years, according to Addis. He says Maxxis expects that trend to continue in 2015. There is one exception to the positive outlook. “In California with our drought, we expect to see some decrease in demand, though our gas prices are down. If there is water to fish in or ski in or jet-ski in, people will go to it,” says Van Ormer. “Ag consumption of ST, a very large sector of our market, will certainly decrease as water restrictions cause the amount of acres farmed to shrink as well.”

TBC introduced the Sailun S637T ST HD trailer tire in January of this year in size ST235/85R16 LR-G, and will be expanding the line with the addition of a ST235/80R16 LR-G size for lower height high-load capacity trailer applications.
TBC introduced the Sailun S637T ST HD trailer tire in January of this year in size ST235/85R16 LR-G, and will be expanding the line with the addition of a ST235/80R16 LR-G size for lower height high-load capacity trailer applications.

A trailer tire authority

Thanks to strong RV sales, dealers are expected to sell more trailer tires. In many cases, they will be selling tires to people who do not fully understand their proper application and maintenance. “Inflation pressure, load carrying capacity and speed rating are the most common questions and where there seems to be the most misinformation,” says Addis.

Answering customers’ questions is an opportunity to become a trusted trailer tire authority to them. Taking the time to educate customers helps earn their loyalty. Correct information also helps them use trailer tires safely. “There is a great deal of misinformation and bad habits on the part of the consumer,” says Tsai, who estimates that 95% of most ST tire failures are due to poor or no maintenance, overloading or misuse and abuse.

“Most consumers don’t do any maintenance or routine checks on their ST tires. Also, most consumers don’t realize that a majority of ST tires are not speed rated above 65 mph. There are only a few ST tires that are rated L and they are not the majority of what’s out there in the market.”

Most consumers also fail to properly maintain their tires, Tsai says. “Any tire that is not set to the right air pressure will lose load carrying capacity. If an ST tire is overloaded then the chances of a failure grow exponentially. In the case of one ST tire failing, it is highly likely that any remaining tires were then subjected to overloading as the failed tire could not carry its share of the load. So it is very likely that the remaining tires suffered internal damage even if for a short period of time.”

At the very least in tandem axle trailers, if a tire fails on one side, the second tire on the same side should also be replaced as that tire bore the most weight when the tire next to it failed. “When trailer owners suffer a failure on one tire alone and only replace one, there is a very high probability that they will suffer another failure soon as now the other tires on their trailer are most likely damaged. These customers are always quick to blame the manufacturer/dealer for poor tires,” Tsai says.

“The first tire failure may be due to road hazard and they replace one tire. Then in a short period of time they will very likely experience multiple additional failures due to the unseen damage to the other tires,” says Tsai.

“This causes a lot of frustration on the part of the consumers as they feel that all their tires are failing for no reason. In fact, it is when they had their first failure that lead to all others eventually failing as well.”

Kenda’s Ostrowski offers some key messages to share with consumers to help build their knowledge about ST tires.

“There are leaders and followers in life, and also in tires,” he says. Passenger car tires are designed for turning and handling, the leaders; ST tires are designed to be towed and carry loads, the followers. The sidewall construction of these is designed for the designated applications.

“If you should use a passenger car tire for a trailer application, due to the more flexible sidewall you must discount the load rating of the tire by 11% and anticipate a ride with more sway. Trailer tires are not generally used as often as a passenger car tire.”

A trailer, when not in use, should be parked on a hard surface and the tires protected from UV rays to ensure maximum life.

“Do not exceed the recommended load designated on the sidewall of the tire,” says Ostrowski. A tire set to the maximum suggested psi will provide the maximum load range. Do not mix radial and bias tires on the same trailer. The load range should be the same for all tires on the same trailer, he says.

After a blowout on a tandem-axle trailer, replace both tires on that side. “The remaining tire was likely subjected to excessive load and as a result may fail in the near future,” he says.

Ostrowski has three recommendations to avoid trouble when towing:

  1. Make sure the trailer is equipped with the proper tires.
  2. Maintain the tires. Ensure that the psi is always checked.
  3. Replace trailer tires every three to five years of service, regardless of whether they look worn out or not.

He also offers maintenance tips for trailer tires not in service:

  1. Keep the tires covered.
  2. Lower the air pressure.
  3. Either park on a hard surface or put the trailer on blocks or jack stands to take weight off the tires.   ■

Related Topics: American Kenda, Ann Neal, East Bay Tire Co., Kenda USA, Maxxis International, TBC Corp., trailer tires

Ann Neal Senior Editor
Comments ( 2 )
  • See all comments
  • D.R.Elliott

     | about 2 years ago

    It is a travesty that the RV industry will sell the consumer a new RV that cost $40k, $50k, $60k, or more and send us down the road on a set of SO CALLED SPECIAL TRAILER TIRES that are lucky to get you off the lot and back home before blowing out the side of your new RV and costing thousands of dollars to repair. As with many things today, it may be BARELY LEGAL but that doesn't make it ethically or morally correct. Shame on this industries greed!!!

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