Thanks for the link. I've checked the article shared by @ingegnere about Ford's rims. They claim a weight of 18lbs (about 8 kgs), which isn't far off Koenigsegg's numbers (6.5 kgs). Carbon Revolution also says that their CR-9 wheels are about 40-50% lighter than OEM aluminium rims, a claim in line with Ferrari's (-40% compared to GTB standard wheels). Here's the quote from their website (http://www.carbonrev.com/faq) Q: How much lighter are they than my stock wheels? A: "CR-9’s are between 40-50% lighter than the OEM aluminum wheels they replace with no decrease in durability or stiffness. CR-9’s on a Porsche 911 reduce the un-sprung rotating mass by over 40 lbs. (almost 20kg)."