Whos running 275/60r15. Having issues

You must be running large bolt axles and the larger brakes. Because if you had factory small bolt axles the 15 x 8 and 4.5 backing space would not work, those tires would be hitting the springs unless you had offset shackles. Factory year with the small bolt axles 15x8 and 4 1/8 backing space fits nice, thats what I run

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Nope...running factory SBP 8.75 with factory drum brakes and no spring perch mods or offset shackles. Mind you, this is on a 68 Barracuda...not a Duster