"ST" Tires On Your Trailer -or- Passenger Car/Truck Tires?

I use car tires on my trailers. Everywhere you look, ‘they’ say using car tires on your trailer is not recommended – it is even dangerous…special trailer “ST” tires are required for trailer use.

I tow quite a bit, over 60,000 miles in the last 10 years or so. In the beginning I was a believer in ST tires because tire and trailer manufacturers recommend ST tires and just about every trailer sold today has ST tires on it.

I had tire troubles with my first trailer. The boat/trailer was only about 3 months old and the tires developed cracks between the tread ribs and wouldn’t hold air. I originally blamed this on the tire manufacturer, but came to find out that while my trailer tires were ‘new’, they had been manufactured 6 years before they were put on my trailer. Outdated ‘new’ ST tires are a common peril, especially if you buy them from a roadside tire store in an emergency.

Here’s something from

http://www.discounttire.com/dtcs/infoTrailerTireFacts.dos

• Time and the elements weaken a trailer tire.
• In approximately three years, roughly one-third of the tire's strength is gone.
• Three to five years is the projected life of a normal trailer tire.
• It is suggested that trailer tires be replaced after three to four years of service regardless of tread depth or tire appearance.

And more from the same site:

Mileage

• Trailer tires are not designed to wear out.
• The life of a trailer tire is limited by time and duty cycles.
• The mileage expectation of a trailer tire is 5,000 to 12,000 miles.

Why Use An "ST" Tire

• "ST" tires feature materials and construction to meet the higher load requirements and demands of trailering.
• The polyester cords are bigger than they would be for a comparable "P" or "LT" tire.
• The steel cords have a larger diameter and greater tensile strength to meet the additional load requirements.
• "ST" tire rubber compounds contain more chemicals to resist weather and ozone cracking.

Storage

• The ideal storage for trailer tires is in a cool, dark garage at maximum inflation.
• Use tire covers to protect the tires from direct sunlight.
• Use thin plywood sections between the tire and the pavement.
• For long term storage, put the trailer on blocks to take the weight off the tires. Then lower the air pressure and cover the tires to protect them from direct sunlight.

Maintenance

• Clean the tires using mild soap and water.
• Do not use tire-care products containing alcohol or petroleum distillates.
• Inspect the tires for any cuts, snags, bulges or punctures.
• Check the inflation before towing and again before the return trip.

Its no wonder I continued to have trailer tire problems - blowouts, irregular wear, weather checking. I wasn’t following the rules:

New tires every 3 years or 5,000 miles.

Store in dark cool place with plywood between the tire and ground.

Wash tires with soap and water.

Get the tires off the ground for ‘winter’ storage and lower the air pressure.

Check inflation before and during towing.

I was encouraged to look at car tires for my trailer because ST tires were such an expensive, unreliable hassle. On the 14,000-mile trip to Alaska with my boat I might have gone through 3 sets of ST tires. There had to be a better way, and there was – get rid of the ST tires, and I did, out of desperation. And lo and behold, the Alaska Highway didn’t destroy the passenger radials on my trailer. In fact those passenger radials went almost 40,000 miles on my boat trailer. And they never got any of the special treatment recommended for ST tires.

No, I don’t recommend you use passenger car/truck tires on your trailer. ‘Just letting you know why I did and still do, complying with this consideration from the Department of Transportation:
How to pick the right car tire for your trailer 

S5.1.2 Except in the case of a vehicle which has a speed attainable in 3.2 kilometers of 80 kilometers per hour or less, the sum of the maximum load ratings of the tires fitted to an axle shall be not less than the gross axle weight rating (GAWR) of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. Except in the case of a vehicle which has a speed attainable in 2 miles of 50 mph or less, the sum of the maximum load ratings of the tires fitted to an axle shall be not less than the gross axle weight rating (GAWR) of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. If the certification label shows more than one GAWR for the axle system, the sum shall be not less than the GAWR corresponding to the size designation of the tires fitted to the axle. If the size designation of the tires fitted to the axle does not appear on the certification label, the sum shall be not less than the lowest GAWR appearing on the label. When a passenger car tire is installed on a multipurpose passenger vehicle, truck, bus, or trailer, the tire's load rating shall be reduced by dividing by 1.10 before calculating the sum (i.e., the sum of the load ratings of the tires on each axle, when the tires' load carrying capacity at the recommended tire cold inflation pressure is reduced by dividing by 1.10, must be appropriate for the GAWR).