The first questions is most likely this... what is 27+
In essence, it's a new wheel format for mountain bikes, burlier than 27" (650b), though not as pneumatically challenging as the current 26" fat-tire standard. Combining a 26" diameter wheel with a 4" width tyre does present challenges for creating a bike with sharp handling... so a new format has been revealed 27+, sharing the standard that's common across bike and component manufacturers and introducing a wider wheel/tire combination.
One of the first manufacturers to launch a bike featuring these new wheel and tire standards is Rocky Mountain, with their 2016 Sherpa. It's a dual suspension bike aimed at adventure/expedition riders.
Rocky Mountain 2016 Sherpa 27+ Features:
Frame: Smoothwall Carbon with 6005 Alloy rear-triangleSizes: S, M, L, XL
Colour: Black/Gold
Fork: Manitou Magnum 27.5+ 120mm
Rear shock: Manitou McLeaod 95mm
Drivetrain: Shimano SLX/XT/Deore 2x10
Rims: WTB Scraper I45 27.5+
Tires: WTB Trailblazer 27.5+ TCS 27.5" x 2.8"
Just to prove the value of the new format, Rocky Mountain dispatch some riders out into the world, including Wade Simmons and Andreas Hestler.
Source: Rocky Mountain Bicycles