I gleamed this from the web site of a large trailer tire supplier.
Question asked and answer provided by supplier
Should I balance my trailer tires?
None of our tire and wheel assemblies come balanced from the factory.
Although some customers do insist upon balancing their trailer tires most (98%) do not. Trailer tires have a tendency to "throw weights". Meaning the weights come off the wheels. This can happen for a number of reasons, but it is not uncommon for the weights to be thrown off when towing a trailer empty (the trailer bounces excessively b/c of the no load conditions) or when making very tight turns on tandem or tri axle trailers.
Furthermore, galvanized trailer wheels are not designed to be balanced. When the steel wheel is dipped into the vat of molten galvanized and then pulled out, some of the liquid zinc always accumulates on one end. Which makes galvanized wheels incredibly difficult to balance. But the galvanized coating does provide one of the best corrosion resistance to harsh environments such as salt water.
Most automotive centers are not equipped with the proper wheel balancing machine to correctly balance most trailer wheels. All of our trailer wheels are a lug centric design. Meaning, that the wheels are centered on the hub by the torque of the lug nuts. Most/many automotive wheels are a hub centric design. Many automotive centers use a computerized "cone" balancer which works great on hub centric wheels, but not on lug centric trailer wheels. In order to balance trailer wheels, an adapter must be used on the cone balancer to correctly balance trailer rims. Check with your automotive center to see if they keep the adapter on hand. Read the details about balancing lug centric trailer wheels here.