Hello, just had to much time on my hands, using a digital scale I weighed a new set of CK ISO hubs, double butted spokes, al. nipples and 317 Mavic rims which came alittle over 1600 grams. Then I weighed a new set of XT disc hubs minus the skewer's with basicly the same spokes, nipples and rims, they came to about 1840 grams. The difference between the complete wheels is only 224 grams, about 1/2 pound, and that is in the hubs, the rest of the wheel parts are the same so the rotating mass is really the same. both of these wheels are mine so Im not flaming anyone who has some King hubs, Im not going to compare the quality of the two hubs, CK's are some of the best, XT hubs are smooth perfromers that when they go, just trash it and buy another one, there is a big difference in price though, and that you could trash quite a few XT's before you will spend the same amount of doe that you would for a King. Will I buy King's again after this, probably, I do like quality parts. there are some other hubset's out there that I might try sometime like Hadley's or Hugi's.