Originally Posted by Kapusta

27.5+ is kinda still working itself out. The initial idea was that a 2.8-3.0-ish tire would allow very low pressures and make riding most trails easier. On its face that made sense as people had been realizing the benefits of low pressures that tubeless had allowed in more standard size tires. And to a large extent it does work out that way. The problem it has run into for some riders is that once you go much beyond 2.4 or so, the limit you run into for pressure is not pinch flats or rim strikes, but the instability of an underinflated tire. This is not much of an issue of you are not an aggressive rider (and this tire size was, in fact, marketed as more "beginner friendly), but as you start to really stuff the bike into corners and land on less than perfect ground, you are losing some control. This is somewhat born out by the fact that most Enduro and DH racers stick to tires in the 2.3-2.5 range. Of course, you can get around the squirmy tire issue by either increasing tire pressure or beefing up the sidewalls. The former kind of defeats the whole point of plus tires, and the latter makes the tire heavy, as well as less compliant (which negates some of the benefit of the lower pressure). However, for less aggressive riding, they can make a lot of sense, and you will often see them recommended for off-road touring. In fact that is actually what the very first plus size tire and bike (the 29+ Surly and Knard and Krampus) were marketed to. I see that the trend has lately been going to something like ~2.6" as the happy medium between standard and plus.