Biggest tire I know of without the use of spacers or major offset wheels is 245 /60 R18.
Search for Jeep Compass Trailpass. It was custom vehicle built by Jeep.
Or do a lot of reading on the Renegade forums. Those guys have done a number of wheel and tire combinations.
Spending time learning the science of the mechanisms of friction, lubrication, and wear of interacting surfaces that are in relative motion
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