Trailer tires are like a black hole on what to choose at times. If it is an older trailer that was designed for bias tires and not radial you have to be extremely careful in a decision to replace bias with radial. Typically older trailers that have bias tires were designed with much stiffer suspensions that require heavier sidewall ratings plus tougher materials to manage trailer sway safely. Radials are not constructed to manage this type of sidewall sway and can accentuate trailer sway as we all know ain't fun at high speed. Bias tires perform the best at max air ratings since the trailer was designed for that as well. The biggest reasons that bias trailer tires come apart is their speed rating which virtually nobody looks at all. Bias tires can have a max speed rating of 65mph and if you pull at higher speeds they will heat up and bad things can happen. Look at the sidewall to determine if the tire has a max speed rating and understand if you exceed it it is not designed for the higher speed. Furthermore if you are towing in hot conditions, the tire can also heat up faster even at the rated speed. Stopping periodically to let tires cool will extend life and keep them from peeling apart. Trailer tires do have limitations that are not even remotely close to passenger tires. If a bias tire is underinflated, it will heat up even faster at over speed or hot environmental conditions. The air temp is lower than the concrete or asphalt road temp so bear that in mind as well.
There are possible radial options that I have heard that might work and usually they are LT rated radial tires which are most costly but do have stiffer sidewalls to help on trailer sway. I have a 4500# rated dual axle boat trailer built in 1989 with bias tires that I contacted manufacturer to see if I could switch and they said absolutely not based upon the suspension of my trailer. It has a jointed tag axle suspension that requires bias tires to work properly. It hauls my boat perfectly without any issues at all. I haul my boat 20-25 times a year fishing up and down the Lake Michigan coast for salmon so it does see a lot of highway. One way to improve bias trailer tire life is go up in tire size if you have fender space, typically it will increase load rating as well and pull nicer.
I also have a travel trailer with radials that pulls nicely with them but clearly was designed to do so.
The points I hope everyone takes is bias tires have a speed rating, keep them inflated at psi listed and check psi before using every time, older trailers are designed for bias due to suspensions, road temp can affect bias tire integrity, radials have softer sidewalls for ride and can adversely affect older bias tire designed trailer handling and bias tires can be safe if managed as bias tires.
I have been trailering all sorts of trailers (boats, 8 horse, travel trailers, flat beds, box trailers etc.) for over 50+ years and have never had a tire failure except when I hit road debris kicked into me. It just takes a willingness to accept the limitations of bias tires and work with them as they are designed.
