And not really sure why BMW used "wobble" bolt in first place...?

Because "wobble" bolts are the correct fasteners for hub-centric wheels.

Standard bolt should be used with lug-centric wheels.

So every other vehicle I've owned is lug-centric, and our stock wheels are not hub-centric?

Not discounting BMW engineer's expertise but why are the E53's the only bimmers I've seen with these wobble bolts.

Back in the day it was easy for me to get replacement powder coated grade 10.9 lug bolts as long as I knew the thread length, pitch, and whether conical/ball seat or not.

Our stock wheels are hub-centric, as well as the rest of BMW's line up, Audi's, VW's, ect. The X5 is the only one I have seen use wobble bolts from the factory.

^^^ This is what I'm saying.

yes, but not 100% correct concerning the OP, maybe.
As an example: e46, e39 and a bunch of other BMW's have all hub-centric wheels, but don't have the wobble bolt. But they ALL have CONICAL lug bolts. The issue some people have, same as with the OP, if using incorrect mounting technique of the wheel it can induce "shimmy".

The correct way of mounting the wheel, is, with the wheel in the air (jackstand or jack), once it's mounted on the hub, try to torque as close as possible to the 130 or 140 Nm the lug bolts. The bolts have that conical shape to force the wheel to be hub-centric. On the e53, the wheels (especially the 20") are heavy, and having the wobble bolt, it will "help" setting the wheel hub-centric.

if the wheel is mounted above ground, and the bolts are torqued only to keep the wheel from falling off, then torqued on the ground with the weight of the car on them, they might get misaligned ever so slightly and as a result you have a car with shimmy induced. It doesn't matter if you use spacers or not, e53 or e39 or e46 etc.

Also, I use spacers on my e39 for years now, never experienced shimmy, and they never got stuck on the hub. As a matter of fact, none of the wheels on any of my cars get stuck. What I do, I use a light coat of antiseize between wheels & hub or between wheels, both sides of spacers & hub. And they still look like brand new after many years of DD-ing through slush, snow or summer. :thumbup:

The E53 wheels are secured with a higher torque (seat pressure is greater). A non-floating bolt would have a smearing effect on the aluminium.

I believe the floating seat bolts were utilized to prevent aluminium deformation of the bolt seating surfaces of the soft aluminium wheels.

It would be interesting to hear for sure from a BMW tech or something too, although you may be on to something.

However, all my VW/Audi experience were around 90 ft lbs of torque so not too far off from the 101 ft lbs here, I wouldn't exactly say its a huge amount of torque for wheel lugs.

I actually clean and lube the contact surface between the bolt and floating cone seat when I remove the wheels. This keeps all the "slip" during torquing away from the aluminium wheel.

ECS does have great Customer Service. I am going to send them the old ones back and they will send me a new set of 12.5mm. They have the same suspicions I have, which is the 15mm might be from a faulty batch.

So we'll see. Keeping my fingers crossed that the new ones work. The X5 looks kind of funny with the 30mm on the rear and nothing up front. I'll update the thread once I get the new ones on.

Thanks for all the input fellas. This is a great forum!