What size will fit?

31' (stock size i think) not a lot or room stock . any bigger ou might have to do the body mount chop to stop rubbing

20" rims are large for an off-road car. better to have smaller rims and more air and tire between rim and ground. the smaller rims/large tires are more bouncy and allow "airing" (adding and letting out air for the condition you face in the outback (heavy sand, snow, large rocks etc)

32 inch in diameter is the largest tire without a lift but it will rub if you articulate the suspension! For flat logging roads or very mild off road level ground no problem! Deep ruts 10+ inches they are going to rub! Go to Tacomaworld.com and use their tire calculator if you insist on using the 20s 275/55/20 would be it but this is NOT AN OFFROAD TIRE! The 55 is the height from the top of the wheel to the top of the tire! It is calculated as a percentage of the width of the tire! You need more rubber between the wheel and the ground if you plan on any moderate four wheeling! I would recommend going back to a 17 inch wheel with a 265/75/17 tire ! These are very common and way cheaper than a 20 inch tire that will probably fail if you attempt any or encounter any rough terrain!