A no comprimise answer to the question of a fat bike specific rim. The ARC 35 rim with a 35mm internal blurs the line between a wide mountain rim and Plus rim and is at home in either application. The ARC 40 is a true Plus rim with a 40mm internal rim width but in a lighter package than the ARC 45 which is the widest rim Easton makes and at the upper spectrum of Plus rim widths. A deep rim profile gives resolute performance and stiffness where others fail. This is not a simple size increase, this is a full re-think. And from that rethink, an optimised rim extrusion with great weight saving and Easton durability.Rim tape, valve and sealant is needed to run a tubeless set-upThe Manufacturer Spec ERD specification listed uses the less common "ERD+" method. ERD+ is the manufacturer listed diameter of the rim at the spoke nipple seat and does not account for the height of the spoke nipple shoulder when calculating spoke length. If unfamiliar with this system of measurement physically measure ERD yourself prior to committing to a spoke length