Halloween Pumpkin

On the fence on what rims to run on the red Duster, I have a set of 14" ralley wheels with new tires, already mounted and balanced, on my Challenger, tires have never touched the ground.

But I bought another set of slot wheels a week or so ago cheap.
But they are a weird size, two are 15 x 8.5 with a 5" back space, fronts I really am not going to use them they are 14" Crager slots two piece wheels, steel and aluminum.

How much tire can I put on the 15" wheels, I have the stock 7.25" rear, have not had time to get the old tires dis-mounted and measure what will fit, or if these wheels with the 5" back-space are even going to fit.