WHAT SIZE DRAG RADIAL SS SPRING '65 DART

A/MP said
Come spring, an index class starts and car must use drag radial. At this point I am using a 7" slick on a 14" rallye wheel. Want to move up to a 15" wheel. How big of a drag radial can I fit w/o moving the springs and using mini tubs?

275 r 60 15's fit with no tubing but you have to move your spring perches, and measure measure measure,to get the correct back space on your wheels.