The wheels are wider, about 6 inches to accommodate modern radials. From what I was told by Wheelsmith, these are modern rims made to look like vintage to accommodate modern brakes and modern tires. There is a calculator on their site where you fill in all of the dimensions so you get the right wheel.
If you go into my Bolt Bucket (click below), all of the pics with wheels in them are Wheelsmith. I put one on all four corners to make sure there were no problems before I ordered the other four wheels. They are 6 lug 15's.
You will want to order your hubcaps from them new. Because they have a contract with the manufacturer to make them special to fit their wheels... OR.. you can send them your hubcaps and they will modify them for you... OR.. they will send you the special parts you need to weld them yourself. Buying new ones from them is the easiest solution.
They do nice work. They will even powder coat the wheels for a price. I got bare steel so I can paint them myself.
When I told Chris at Wheelsmith what I was working on, he didn't even ask me for the dimension sheet, he knew what I needed and he sent me the right ones. Nice quality as far as what I know about wheels.
