Quick Answer: It’s important to note that the “++” callout in Spank published ERD measurements for all our rims, refers to the height of the heads on the nipples you are using in your wheel build. You must add 2X nipple head height (specific to the nipples you have chosen), to the ERD when calculating spoke lengths. ERD and “++” - In the past ERD was usually communicated as a calculation including a standard nipple head height, (ERD = Inner Diameter of the Rim + 2x Spoke Bed Wall thickness + 2x Nipple Head Height). However, in recent years many new standards of nipples have been introduced, and nipple head heights vary. For example a standard external nipple has a 2mm head, while a DSN type nipple has a 4mm head. For this reason, Spank communicates ERD without including nipple head height, so the user can add the exact height of the nipples they have chosen for their build, (Inner Diameter of the Rim + 2X Spoke Bed Wall Thickness = ERD ++).  If you are using an online spoke calculator, and the ERD value is expected to include nipple head height, then you may need to add the head height of the nipples you have chosen to the spoke length offered.