The trick with the trailer wheels is weight and heat. With 12" wheels and 60+ MPH your trailer wheels will have to turn up to 1.5 (approximate guess but you can figure it out with the circumference of your tires) times per tire rotation on your truck or car and the trailer hubs get hot as they are smaller as well. Too hot and they seize, they seize and you stop....not good. 14" will run a little cooler and handle the weight better especially over all the bumps and holes in our highways. I also use "bearing buddies" on my trailer so I can make sure they are lube'd and running well. Carry a spare, seems cubersome until you need it. You could probably get by with 12" wheels, and I've seen some who have, just check your hub's every stop. I pulled 2 4wheelers in my trailer up and over the Smokies, about a 1200mi road trip at Thanksgiving and not a hitch. Have only hauled my bike once but it was fine. Also make sure your trailer is strong enough to have strap holds to keep your bike down. You'll have to strap it down almost to the limit of the forks/springs to keep it from bouncing, not good. I've seen some of the cheaper trailers crack and break welds (thankfully made it but some frantics reenforcement needed) from the tension of strapping a 700lb bike and the bouncing around on the roads.
