Drag Radials 235/60/15s

I tried it with factory 15x7 with 4 1/4'' backspace steel wheels and they would rub hitting dips in the road surface and on turns. I went with 15x6'' factory steel wheels(painted Blue) and no problems. All suspension in the rear was 1964 stock with new bushings.. 235/60/15 BFG drag radials.