Most Cobra replicas have a chassis based on a 4 inch main frame member although the relationship of that frame member to the body is not always going to be the same. On ERAs they recommend a frame clearance or height at the front of 5-1/4 inch and 5-3/4 inch rear. I run about 5-1/4 inch front and rear.
But it's going to depend on the manufacture, the wheel well opening shape, tire size & height in addition to your preferences and local road hazards.