Belt Mounts
On most BMWs, only the belt receptacle is attached to the rail, whereas on the Z4, both the lower belt and receptacle are attached to the seat rails. That means you will need to purchase 2 kits (or 4 brackets) for both seats. Your options include
VAC and
Rogue Engineering. The only downside with these is they both attach to a fixed point, instead of moving with the seat like the factory setup. Therefore I chose to go with
PS Designs whose brackets sit in between side mount and slider, thus mimicking the factory setup.
Note Planted floor mounts include welded fixed tabs for belts so you don’t need to purchase additional brackets.
Belt Receptacle
Unless you have Cobra Nogaros or Recaro PP ABE seats, chances are you will have difficulty routing the factory lap belt properly. The answer, however, should not be securing the belt over the side bolsters -- that is very
dangerous and could lead to
submarining during a crash. It's imperative you have the factory lap belts positioned over your pelvis. So there are two options I am aware of:
- Option 1 - Use an aftermarket non-rigid belt extender with the factory receptacle OR
- Option 2 - Replace the factory receptacle with a rear lap belt (e.g. E92) and purchase a separate clip only
Neither is perfect but they’re better than nothing. Option 1 retains the factory pretensioner but you're putting your faith in an aftermarket product. Option 2 is simpler, but you have to relocate the factory receptacle under your seat and purchase a spare belt clip so the car won't give the seat belt warning. FWIW I went with option 2.
Occupancy Sensor
The OC sensor can be dealt with coding on newer platforms but I don't believe that's the case for the E85/86. So the easiest option is to buy an aftermarket emulator from eBay. I did this on my prior Z and it worked flawlessly. Just be sure to have the seller confirm it will work with your Z4 as there are different versions for different BMW chassis. Alternatively, you can always find a spare factory OC sensor on eBay for ~$75. You just need to make sure you can access your seat cushion to install the sensor.
Note you only need one occupancy sensor for the passenger side and the factory OC sensor part numbers differs for pre-facelift and LCI (06-08) Z4s.