Dano711 here is a link, no you don't have to replace the drums. http://www.trailertiresandwheels.com/17.5-Aluminum-Trailer-Wheels
Call me cheap, but....8 wheels and tires for my 6 wheel TH (including 2 spares) adds up to over $5k...
Actually, you only need 6 wheels and tires. Your current spares are the same size as the new tires, but you won't be needing the spares or braking the side of your slide outs. $$$$ big dollars to fix. Worth it in the end if you don't feel like changing blown tires, at night, in the rain, on the way to your race weekend. Just a thought, your mileage may very.
I did say might, 16" wheels are available as both 5 lug and 8 lug variety, 17.5 are only 8 lug. I went the G614 route as getting a tire while traveling is much easier for a 16 than a 17.5 wheel. Caveat the G614 are almost always special order tho just the ability to get a temporary replacement while traveling if you destroy a tire, (I never had one blow out in over 12 years of towing with them)
I had the same goodyear bias plys on my tow dolly for 10.5years before one finally blew out. Way overloaded it with econoline vans and whatnot all the time too. Guess I got lucky.
I had these on my 46' trailer. They were the worst tire I've had on a trailer, ever, I've been towing trailers since the 80's. They would last between 5 and 30k miles. not one ever wore out. They all exploded with good tread. Plus at dealer cost they are right at $350. I switched to a P.R.C. (Peoples republic of China) and have had much better luck. They have been on there since the end of 2012. Better tire, and they cost just under $200. I was afraid of the P.R.C. tire at first, but I decided that the Goodyear sucked, so at worst these would also. But they would be cheaper. Turns out, the Chinese are way better at tires than Goodyear. I know a lot of people running the Bridgestone Transforce with good success.