There’s a number of things to consider when looking at wheels. The larger the wheel diameter, the more energy to get it spinning. There’s also bearing and road friction. One thing that would reduce drag would be to make the tire and rim narrower but the trade off would be weight capacity. [/quote]

IMHO the friction from larger dia wheel/tyre combo on a boat trailer would be virtually nil compared to that of overall wind-drag at 40+ mph. I think it would be a no-brainer in most cases.

Tiger Mike