You can go A LOT of places in a 2wd vehicle. The challenge is when that well manicured gravel or dirt road gets wet, or if it becomes off camber. Could you do something like the Mendocino BDT in a 2wd Tacoma? Sure, but I wouldn't attempt it when the trails are wet or muddy. Most drivers can probably take on trails rated rated up to a 3 in a 2wd (when dry), and more skilled drivers could probably pick their way through a trail rated 4, or even 5.