I think my XC70 hates its tires!--need advice! - Wheels and Tires Message Board

Hi all, first-time poster with a problem I haven't experienced before. Sorry for a long post, just trying to lay out all the facts and look for some feedback.

Never had a tire-matching problem on my BMWs, but we have a 2007 Volvo XC70 that is working our last nerve.

The car came with 16" wheels and we are upgrading to the 18" Atlantis wheels from an XC90 (SUV). This upgrade requires hubcentric rings (od 67mm, id 65.1mm). We purchased Falken Ziex 912 in 235/50/18 size and had them mounted last week. The vibration at highway speeds is unbelievable, and only gets worse as speed increases. We have taken the car back 3 times now, and just yesterday they used a Hunter road force machine to balance. 3 of the 4 tires/wheels required (in their opinion) quite a bit of weight to balance out, but they did balance to 0. However, we noticed that two of the rings were missing, so only the front wheels had the rings. Don't know if they never had the rings, or if they were lost during one of the trips to the shop.

They are ordering the replacement rings, due in tomorrow, however the amount of vibration we get just doesn't seem like it could be totally related to two missing rings that are less than 2mm thick.

My question is, ARE THE TIRES ACTUALLY TO BLAME? Are they just not a good match for the car? The tire shop wants to swap them out for (considerably more expensive) Yoko Advan ST tires, and I'm willing to do that. But what I do not understand is how the tire interacts with the car to such an extent as to cause a terrible virbation...it seems like if it balances on the road force machine, and the hub rings are the proper size, then it should work on the car.

You guys have any thoughts or experiences that would be helpful?

Thanks!