37's are pretty ideal for most, but we used to say that about 35's and before that we said the same about 33's. I think 40's are on the cusp of being the ideal size these days, but they are probably too much on the wrong side of diminishing returns to truly take over. They are certainly too big for the Overlanding world.Only trails I see requiring 37" or above is rock buggy trails in reality. 40" has to be a buggy trail. To me 37" tires are optimal, but 35s will do about anything you want, just not always as easy. Take the Rubicon, you can do it on 33s with endless stucks and recoveries, with 35s its very doable, with 37s almost too easy for a good driver. Fordyce is the most difficult overlanding trail I can think of that is not just a buggy trail up a dry wash, or even the new slick rock obstacles in California. Those I would definitely want 37s and 40s would rock. But that sure is the minority.