Wheel to spring clearance

4.5" backspacing it about the max on a Dart. Depending on what tire you're using it may or may not be hitting the spring. A thin spacer (1/8") might sometimes be needed. A 225 tire will fit, a 235 tire might fit, a 245 or bigger tire probably won't fit. But every car is unique. And a Duster/Demon has tons more room for tires than a Dart, so Coyote Jack's advice really doesn't apply here.