Mock Up 335/30/18
 

So I am at the point in my car where I had purchased a cheap set of 335/30/18's off ebay for mock up, they are Hoosier DR2 slicks. Off the rim.
The dilemma I am having is the tire seems to be rubbing in my DSE minitubbed 69 camaro. The hoosier website says they measure 13.2 inches wide on a 12 inch rim, but i am getting 14.25 with a tape measure. Is this because they are used or off the rim? In the center of the wheel well i have about 15 inches of space but it seems to be more tight along the front and back of the wheel well. Any advice would be great. Already have a set of 18x12 wheels and really dont want to run a 315 on the car and that size rim. Again any insight would be great, just trying to get this figured out. And the tubs are in welded/finished. No more moving anything around.