OOPS - posted on wrong forum. But if anybody on this forum has input in general, I'd welcome it.
New tires on our 2019 GLC300.
The tire shop has not been able to get a good balance on the tires. I have gone back twice after the original mount and balance, and it's still off.
After the latest effort, it is worse, but instead of feeling like a balance issue, it seems like I'm driving on rocks.

Which makes me wonder just how the tire shop is fitting the wheels to their balance machine.
So, This Question:

A hub adapter centers the wheel and should always be used. A rubber surfaced cup or a lug type adaptor with the spinner nut installed on the shaft pushes the wheel against the hub adaptor and spring loaded shaft flange, centering the wheel and securing it on the shaft.
If the shop is using a lug type adaptor without a hub adaptor they are doing it wrong.

Mercedes and BMW are hub centered wheels.

Thanks. I know that, and I should have been more clear. I was asking about what a tire shop might use, if they didn't know or lost their adapters.
I think I am headed down a path of incompetence with this new shop.
I'm trying to get back up to speed with equipment they might try to use.

I have had very good luck with Discount Tire in spite of the cheap sounding name. They normally have well trained staff and Hunter Road Force Balance machines. The RFB seems to be the best method since it simulates real load conditions. I’ve had them do two sets for our Audi and Winters for my 53. No vibration at any speed. Many years ago I had a set of Goodyear’s on a new Ford Explorer that could not be balanced (2 tires) and all four were finally replaced at no cost to me. It’s doubtful that a bad tire today would even leave the factory.

I have had good luck with Discount Tire, too. Seem like the most reliable stores, with good training and up to date equipment. Unfortunately the nearest is an hour away, so I am trying a local store. I hope I haven't gotten stuck with a bad one.