[abbike18]

I installed the X3M rear strut brace a few days ago.

First picture is the required parts:
Rear strut brace, 51718077347. I got mine from eBay, used off a crashed car for $190.
Left and right brackets, 33308077349/350. I had to order these from Germany, and they are required for the install. They replace parts on the M40i that are smaller and don't have the bottom screw holes/mounting area for the actual strut brace.
Rear subframe mounting bolts (2x), 33326760340. The BMW instructions say to renew these screws. I don't always renew when the BMW instructions say to, but the torque on these is 100nm plus 90 degrees and they are major structural bolts, so I replaced them.
Strut Brace to brackets (4x), 51718082205. You need these, there is no equivalent on the M40i. Torque is 38nm.
Strut brace to chassis bolts (8x), 07149390155. These are optional. There is an equivalent on the M40i chassis, but what comes on our cars are class 8.8 and the X3M uses class 10.9 bolts. Also, the torque on the M40i is 25nm and on the X3M is 38nm. So I decided to upgrade these bolts given the increased stress the brace will see.

Install is pretty straight forward and obvious. You do have to remove the torsion link (torque on the big bolts is 100nm plus 90 degrees). I did have to make one small modification to the heat shielding to get the brace to fit through, you can see it in the second picture. A little tin snip action and it was all done.

Driving impressions - well first off the sunroof doesn't make a creak anymore every time I back out of my driveway and off the curb. So it is definitely adding some rigidity. Drive wise yes the back end feels tighter and more rigid, possibly making the car feel more balanced as the rear wheels are more where they would be expected to be. Keep in mind I am heavily tuned, turbo upgrade and with the locking diff. I haven't really sent it yet, but if I have thoughts on it will comment here.