I can't think of one single reason to run bias tires
on a trailer unless it is perhaps a 5th wheel. Bias tires
develop more internal heat and so are more prone to blowout. They develop a flat spot when left sitting for extended periods. They wear out sooner, ride stiffer, and are more likely to cause vibration from poor balance. I thought this debate was 20 years in the grave
. The one possible plus to bias tires
is that they have stiffer sidewalls. They can resist the sideloads generated by 5th wheels in heavy jack knife. ST radials are supposed to handle that though. I wouldn't have a bias tire on anything. I'm old enough to remember how bad they were!