It is the way they are forged. I will look for the explanation on the difference and try to post it, or you can research it. You have to ask what process was used in the making of the wheel. CNC machined wheels will cost a lot more for example. 3 piece rims are outrageous in price, but are the best. There are a host of 3 piece look a likes. So, you have to be careful there as well. I just bought a wheel without researching it, and it was a bad mistake I would normally not make...but hey, I'm getting old...lol. Just be careful, because these copies look like the real deal. I love the look of the rims....but I kind of figured I would have a problem with them and I did... The TSW I just purchased are a risk as well, but we will try them. The E model MB is a very heavy well built car... I would think the XF would be a little easier on these kinds of wheels, but I wouldn't chance it myself again.