Sport seat modification for a "wider" frame


Apr 6, 2018
Dallas, TX but soon to be Cocoa Beach FL
2012 z4
Finally got everything I needed together to pull the front seat out and see what I can do to take some pressure off my thighs. I like to man-spread, and the side bolsters have always made driving more that an hour uncomfortable. There was another thread where someone mentioned about trimming off the seat side bolster supports, so hey, here we go with some more detail.

Taking the seat out. Seat all the way back, 2x T-50 torx bolt to remove. Move the seat all the way up (vertically), need to do this to get to the underside of the seat later. Move seat all the way forward, and remove the rear 2x torx bolts. Recline the back as much as you can, well just get a gangster lean going (120 degree'ish), makes things easier later.

At this point, disconnect the battery (you put the top down already, right?) and wait ~15 min or so. Let the electrical system discharge before we unhook the seat (i.e. airbag). Under the seat is a yellow plug. On the inboard side is the slide portion (typical BMW plug) that has to slide out for the plug to come apart. Give it a good tug, and the plug separates.

Seat belt cover, pull the rear portion out horizontally to you, then it should slide back and out. T-50 again to remove the seat belt, then the seat is free and can be removed. Admire all of the "stuff" you have accumulated. I found $1.37 in change, that black plastic bolt cover that fits behind the door handle, a pen, and a bunch of leaves.

Visual person like me? BMW seat removal

So seat is out. Flip it upside down and lets get to disassembly.

First thing (sorry no pic of this), is the plastic cover for the bottom of the thigh support. #6 seat parts diagram Three tabs go into the seats, and outer 2 you can push in and unlatch. Middle one is just pressed in, so give it a pull after unlatching the other 2 and it pops out. Found a pic:
seat 5.jpg

The next plastic piece to remove is the seat switches (# 1 in diagram above). This has a few tabs (6 if I remember) to pop off and remove After this, you can see the channel where the leather seat cover is attached. Begin at one edge and work your way around and unattach. The back of the seat has another 3 channels to removed. There are also 2 straps that need to be unattached on the hinge (right side of pic, little black strap). Once all of this is completed. push the rear cover up though the seat crack and uncover one side of the bolster. In the crack, attached to the cushion, is where you will find 4 hog rings (circular fasteners) that need to be cut/disconnected (2 each side). Once these are free, you can proceed to removal.

seat cover 1.jpg

From here you can feel the metal support rod that we will be removing. There are no wires in the section, but be careful nonetheless. Begin trying to expose the metal bar:

seat 2.jpg

This the end facing the rear of the car. It loops around and attaches to the front of the seat, which is where I will cut. Chase it to that curve, and pull out the cutting tool of choice. I had grinder and a hacksaw ready, then I thought...

seat 3.jpg

Yep, bolt cutters. Where the piece is in the pic is roughly where it is in the seat. The cut is almost horizontal, so I'm not worried about anything poking up/cutting anything thought that much foam. Here's what the seat looks like post cut:
seat 4.jpg

From here it's recover, do the other side, and button it back up. Vacuum up the mess under the seat, clean the heck out of your seat while it's out too (headrest really just pops off), contemplate swapping out those subwoofers eventually, and reinstall.

Thoughts after a few rides. This does less that I thought, and it's perfect. The pin-point pressure in my thighs is gone, yet the seat is retaining the support and structure. I'm a bigger guy, so at least the mid-thigh pressure is relieved and there is some give/flexibility now if I need to move around in the seat. Pretty darn happy about this one.
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Feb 23, 2018
2011 335is
Woaaaaaaah this is a modification I haven't seen before.

Very cool! That seems like a pretty easy mod for more comfort.

Reminds me of Herman Miller office chairs and the need to get the bottom correct for size... otherwise it cuts off circulation to the legs. Aeron has a few sizes and some people are not compatible at all.


Lieutenant General
Staff member
Aug 11, 2017
E89 Z4 35i, F10 535d
Ballsy mod and good doc - thanks for sharing this!

Nov 10, 2018
2011 BMW Z4 35i
Well done! I had to make this modification myself. You did a great job of showing how this is done. I also took the back apart because side bolsters were brusing my ribs. BMW used the same round stock to form the shape of the (for lack of a better term) wings. On the back it was much easier to bend the round stock wings outward a little to give me a little more room. I can still use the seat adjustment air bag system to snug things up if need be.