I know the leather-Z kit has been out for a while. it just never sat right with me that a) it was almost 400 for the kit that fit the 335i ( tire + tools + spacer & bolts)
b) you needed to use a 15mm spacer to get it to work.
digging through the ETK, it looks like the leather-z spare is the spare from the E46 cab.
a little more digging shows that the E60 550i uses front brake rotors the same size (348mm) and thickness as the 335i. brake calipers look to be of approximate same size.
the compact spare for the 550i is:
the offset is close to that of the E46 spare plus spacer-- ET 15 for the E46 spare wheel + spacer vs ET 18
now the fun part. BMW sells a retrofit spare kit for the E60. it includes:
the wheel +tire diameter is within 2% of stock tires
total price from tischer BMW, for the whole retrofit kit listed above, before shipping, is $239.
I've ordered up a set, will keep everyone posted as to if it works. if it doesnt, i have a new flower planter. if it does, a spare that works without having to deal with the spacer, and for a lower price.