Originally Posted by gr8000
A couple of follow on questions (sorry that all this comes in bits & pieces):
1. Can the wheel & tyre fit securely in the trunk (eg by taking out the BMW OEM mobility kit and the soft material that keeps it in place)?
2. I am not sure I understand what the centering rings are for and where are they placed. A hint will be much appreciated!
The spare tire won't fit under the trunk carpet; the space under there is far too small. None of the E9Xs have a spare tire well under the carpet, but the M and dual exhaust 335s are particularly bad in this regard (since the floorpan has been reshaped to make room for the giant mufflers on these cars).
Carrying the spare thus means you lose some trunk space. It's not too bad; I can still get all of my normal luggage in the trunk (on top of the spare).
I use bungee cords from to the tie-downs in the trunk to hold the spare in place. It's kind of cheesy looking, but it gets the job done. The jack and a lug wrench fit underneath the spare wheel; I've wrapped them in packing foam, which keeps them secure and prevents them from rattling around.
Horrible pics taken in the dark with my iPhone are attached.
EDIT: The centering rings go in the center of the wheel, in the large hole at the center of the lug nuts (the hub bore?). This hole is designed to mate with the hub on the wheel, in order to center the wheel properly, but since the X5's hub diameter is slightly larger than the E90's, the wheel doesn't quite center itself when you put it on the hub. The centering rings are literally just plastic rings that fill the (very narrow) gap between the spare wheel's hub bore and the hub of the car.