"Installing buck seats appears more complicated than it actually is. I expand on the options and the one I selected for my E46 M3. Hopefully this helps you in your selection!"
The OEM Configuration
Most BMW M stock seats are electrically powered and installed on sliders. They have these small, powerful electrical motors that can push our bodies of varying weights forwards and backwards.
The motors are those grey cylinders underneath the seats. There are quite a few.
Only 1x is used to power the sliders.
The others are there for other electrical functions on the seats themselves that aren't re-used when fitting aftermarket bucket seats.
Determine your goal!
You want it to slide, and remain electrical?
Brey Krause side mounts + OEM sliders.
This is what I personally picked for my E46 M3. I wanted to keep the electrical power sliders and I wanted a simpler installation.
The Recaro Pole Position ABEs require the R-9222 (Driver side) and R9223 (Passenger side) mounts.
They are height adjustable with the slots showcased below. Allowing you to adjust the seats height, and tilt according to your preferences and your M car's flooring.
The E46 M3 has the front of the mounts sitting higher than the rear on the flooring. Keep that in mind when adjusting your seat outside the car!
Note: if you're planning on installing Recaro Sportster CS, these are bottom mounted and will require Brey Krause's bottom mount solution (R9246).
The BK side mounts are well engineered and designed to work with the OEM sliders. They come with all the required mounting hardware along with washers for adjustments to the seats angle.
They offer the option to run the electrical power sliders. They provide all the wiring and brackets for you to do so.
In order to activate the powered OEM sliders, you will need to re-wire and pin the OEM seat harness.
The picture above shows the OEM electrical motor and rod having been transferred to the new Brey Krause side mounts.
The harness is connected to E30 Accessory buttons (SKU 61311367373) as pictured below. You will need 1x per seat.
These aren't exactly cheap. Running electrical seats adds 160$ in materials + electrical wiring labor if you won't DIY this.
Brey Krause provides all the necessary instructions to do this.
You want it to low, fixed and with shiny Recaro side mounts?
If you'll be tracking your car extensively, and/or desire a super low seating position. this is for you.
To run this configuration, you're ditching everything from the OEM seat sliders and rails.
You can optionally run universal Sparco or Recaro sliders with these. I find that solution pointless considering the BK Auto solution presented above, unless you really want the shiny Recaro side mounts.
Floor Mounts + Recaro Side mounts!
New Chassis Specific Floor Mounts
First things first, you need new floor mounts. These replace your OEM sliders and are bolted directly into the OEM mounting points into the floor.
I have not yet curated any floor mounts as I don't have hands on experience. Below is from a German brand I may work with.
The various threaded holes are used to position and bolt down the seats to the floor mounts.
Recaro Side Mounts
We've all seen the magazines - we've all wanted this at some point in our life.
This is it. I can source these directly from Germany for you.
These are made from steel and feature the famed RECARO logo.
You just want it even lower and fixed?
Brey Krause Floor Mounts
BR arguably makes the lowest fixed mounts for M cars. No sliders, nothing. It's a pair of mounts directly bolted into the chassis and your seats.
It's also arguably the safest solution out there. They are DOT and SAE approved for most BMW M applications.
This buttons up it up!
Stay safe out there.