I'd be much more worried about the pedals or handlebars of a high quality Roadmaster(tm) bicycle falling off than the bearings seizing. Personally, I wouldn't take that kind of bike over 12 mph these days unless I was wearing body armor. I used to ride that kind of bike, and I destroyed at least a half a dozen of them before I got the message. In my experience, you're lucky if the bike makes it 100 miles. And hey, that's only 2.5 hours at the pace you'll be going.