largest rear tire without relocating springs or?

Best thing to do is measure twice before ordering. It's pretty simple.

Get under the car and identify your two contact points. Usually the inner fender lip and the spring. Measure between the two. That's your potential maximum tire width. Then measure from the mounting surface of the rotor/axle (where the rim mounts) to the two contact points. This will tell you what your back space should be. And where your rim should be centered for max wheel size. Leave a minimum 1/2 between contact point and the tire. The rear axle will move back and forth under cornering.