65 Barracuda slant 6

It depends. What rear end do you have?

With a 7.25 rear I have a 245/60-15 on a 7" rim. Fronts are a 215/65-15 on a 6" rim. 66 Valiant. Thats about all I can do and still have clearance.

You need to check measurements on your car, clearance can be different even on the same year and model.