Yep when we were kids our boats (mine and my brothers) were double decked on a trailer with 8" tyres and I can't recall ever having any dramas. But like I said 'in a perfect world' I'm running 13" on my boat trailer at the moment and will be going to 14" at so stage to use a couple of aluminium mags I have here. Its not so much the bearings etc that would be the problem, the tyres getting hot and melting from spinning so fast - I have seen tyres melt and disintergrate, and tyres poke the wires out the side. But then again while our season is on, and trailers are being used carting boats in regattas etc.. its usually pretty bloody hot to begin with.

Regards