What is the Largest Tire that fits stock 20" wheels with little to no rubbing?

[ryanjl]

The black one is an LR3, which came with 18's from the factory. My guess is those are either 265.65.18 or 275.65.18.

The silver one looks like it's running 18" LR3 wheels with 1.25" wheel spacers, and probably 265.60.18

 

[TrinidadLR4]

If anyone knows the answer to this: I have been running these 20in RR supercharged wheels which have a 58mm offset. They fit fine with 275 55 20 tires but since the offset is so high, they are quite tucked into the wheelwell. It doesn't quite look right and I am thinking about adding spacers to move them out a bit. Not sure what spacers I should get - I just need the wheels further out and more flush with the fenders. Having never run spacers on a Rover, guide me on what to look for. Thanks!