Thanks all. I ended up going with E-rated Good Year Endurance tires (ST235/85R16), and had the valve stems replaced with high pressure stems to accommodate the 80 psi tire pressure. My previous (and well aged - 10 years old) Carlisle Nextrail tires "looked" to still be in excellent condition with plenty of tread left and no side wall cracking, but upon closer examination the tread was actually starting to crack and peel off the belts! Unfortunately I didn't catch this tire condition while my boat was in the water. Not wanting to trust these tires to tow my boat anywhere I ended up having to lift both my trailer and boat (Fountain 38EC) to get the tires changed. (Thanks to TireRack.com and two 20-ton bottle jacks). The process was quite a chore and would be have been SO much easier without the boat being on the trailer. I plan to keep a much closer eye on the condition of my trailer tires from here on out. Lesson learned.