Borealis Carbondale 27.5+ rims. Double walled carbon construction. This is a great option for those looking for a summer rim that will hold up to whatever you throw at it, while still allowing for the use of up to a 4-inch tire. Double walled construction and wide rim profile gives you a stiff, durable rim and a nice tire profile. Rims are tubeless-ready and include rim tape and valves.