Some companies are now making 2.6 and 2.8 wide tires for standard rims. Will these fit in a standard fork? Have a Fox 34- looks close on the 2.6 but the 2.8 seems unlikely. Thought it might be nice for winter riding in Colorado.
Assuming you have a 27.5 fork, a 27.5×2.8 will probably not clear. Keep in mind that you need to be able to clear the arch AND the crown. To check the crown clearance, let all the air out of your fork and compress it completely. If the tire touches the crown DON’T RIDE IT!
A lot of 29er forks will clear a 27.5×2.8 though.
Another consideration is rim width. If you’re running a 2.6 or 2.8 you’re going to want a wider rim (like 30-40mm wide). Running a really wide tire on a relatively narrow rim can be a recipe for disaster. I tried putting a 2.8 on a 25mm internal rim and I could easily rip the tire off the rim in a turn.