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Trailer Tire Rating

Originally Published in Trailer Life Magazine

Q. I purchased a new 27-foot fifth-wheel. We had traveled 3,500 miles when one of the tires separated like an old recap. We had just stopped for fuel and had rechecked the tire pressure after lunch, so I know the tire inflation was up to snuff. Upon separation the tire damaged the door and side of the trailer, but the good news was we were traveling at 60 mph in the slow lane with no traffic. Looking closer at the tire load rating of 2,540 pounds (ST225/75R15/D) per tire and the gross axle weight rating (gawr) of the trailer at 11,035 pounds, I am concerned that the tires are rated 900 pounds less than total trailer weight.

Can you give me information on the load rate for tires when the vehicle weight is known? I would think it would be at least as much as the gawr, or greater. Also, how would you rate Carlisle tires? I had not heard of them until the purchase of our fifth-wheel.
— J.C., Mesquite, Nevada

A. Carlisle is one of the less-well-known brands, J.C., and we don’t have any information about those tires beyond what may have been in your owner’s information packet. As for the tire failure, you may want to run your loaded trailer over a scale to check its actual ready-to-tow weight. An overloaded tire could have explained the failure, or it could simply have been a random tire problem, too. The total carrying capacity of the tires at maximum inflation pressure, as molded into the tire sidewall, should equal or exceed the total gross axle weight rating (gawr) for the trailer. If the tires are rated less than the axle gawr, the manufacturer made a mistake in using those tires on that trailer.

Check your trailer’s gawr again, and make sure you aren’t looking at its gross vehicle weight rating (gvwr) by mistake. If the tires are underrated, I’d take the unit to the dealer where you bought it and request replacement tires, and wheels if necessary, to result in a suitable match of tires and trailer. Because as much as 15 percent of a fifth-wheel trailer’s weight is located on its hitch, the tires may not be rated to carry the full trailer’s weight. As long as the tires are rated to handle the weight carried on the axles, by way of equaling or exceeding the trailer’s combined gawr, they’re fine.

— J.J.

Jeff Johnston, Trailer Life’s technical director, started RVing at age 6. During his more than 20 years as a writer/photographer, he has worked for Truckin’ and Four Wheeler magazines before joining TL’s technical staff in 1985. Johnston also has produced an award-winning travel video and TV commercials.

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