Wheels n Tires

Tabitha has 15x6JJ stock wheels with a 5 on 4.5 pattern.
You can buy new replacements at Vintage Trailer Supply. [This just in: Found the wheels for a steal at the Nuera Transport eBay store.]
The trailer had 215/R75 15 passenger tires on it. [Passenger tires are as you know unsafe for use on trailers as the sidewalls aren't meant to carry the load.] The 215's were also too wide to remove the tire without dropping the axle off of the jack. That's one Big Fat Drag. I went to a ST205/R75 15 8 ply, D load GT Radial tire which I found at www.tires-easy.com out of Oregon for close to $60 each. With shipping, mounting and disposal [by a local shop recommended through Tires-Easy] the total was $350 for four tires. A good idea is to repack the bearings while the tires are off especially if you are uncertain about their condition. I learned that lesson the hard way in an old '63 Rambler American.  Did you know that bearings are basically the only thing keeping the wheel on the axle?  I didn't learn that until the whole wheel came off. 
Long story short - I met a friend at a theater for a movie - parked next to her standing on the sidewalk.  As soon as the car stopped the whole wheel fell off.  I popped out of the car unaware... thought she had a funny look on her face.
Tire width for rims are variable. The tire width range for 15x6JJ wheel is safely between 185 and 215.  I opted for the widest tire that fit the trailer properly... in my case 205. Considering the trailer is 4,280lbs and I am driving mountainous roads - I feel safer with the wider tire.