Not all Darts have enough space for 255/60/15's. They will fit some Darts, not others. I've seen the measurements from cars that don't have enough room to do it without cutting or rolling something. The dimensions and measurements are right in this thread, the math doesn't work. You say to measure to get proper clearance, but if the measurements come up short you just can't get the clearance unless you start cutting. How do you figure you can get the clearance when the measurements tell you there isn't enough space?
These cars were not all the same from the factory, I've seen differences in the quarter measurements that are different by almost a 1/2". Some cars have enough room for 255's, some do not.