"The average car tyre will have a working load of approx 1200 lbs and my trailer weight is around 1000 lbs per wheel so the loadings will be similar. (I usually have 2 boats and all my stuff in the trailer). You should use a tyre designed for whatever load you are putting on it."

Hi Mike
It's not so much the load, as the flex of the sidewall...from what I have read on the subject, the sidewalls are much stiffer on dedicated trailer tires which helps to keep trailer sway to a minimum...granted this is a much bigger issue with a heavy utility or power boat trailers.

Regards,
Bob