Choosing Race Seats for the M Coupe

[3002 tii]

After picking up my M coupe few months ago, I've been slowly converting it to a dual duty track car. When everything is said and done, I’m hoping it’ll be a modern take of a Z4 M ‘CS’. I’ve addressed wheels, suspension, braking and engine so the only item remaining was interior, namely the seats.

I had Recaro Pole Positions on my previous coupe, so I wanted try something a little different this time around. With the goal of maintaining a factory look, I looked at different P-car builds and that's when I stumbled upon this beautiful 991 GT3RS built by GMG. The car is fantastic on every level but what really stuck out were those Sparcos. At $1499 MSRP the Sparco QRT Performance is hard to beat in terms of value. Its FIA rated, lightweight (9.9lb shell), offers very low seating positions and comes in that beautiful red leather.

With any aftermarket seat install you’ll need mounts and brackets. Unless you buy all hardware from the same manufacturer, you should be prepared to modify (i.e. drill) some pieces. It’s almost unavoidable especially for our cars where spacing is tight.

1. floor mounts
2. side mounts
3. harness/belt mounts
4. solution for the occupancy sensor

Silverstone E92 w/ Fox Red interior, courtesy of EAS

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Hardware

Side Mounts
My first preference is Brey Krause since they integrate with OEM rails. It's arguably the safest and the most cost effective since you don't need to purchase floor mounts, sliders or receptacle brackets. In other words, the BK kit is an all-in-one solution. Unfortunately for me, the BK side mounts were not high enough so I ended up getting Sparco's seat-specific mounts.

Floor Mounts
Floor mounts come in 2 flavors -- the first is the single piece frame offered by Planted, Sparco, etc. The second is the 2-piece rectangular mounts offered by VAC, Bimmerworld, etc. The advantage to the 1-piece mount is they are usually designed to be vehicle specific so they'll bolt in perfectly. However, they won't offer as much adjustment range like the 2-piece mounts.

If you go with the 2-piece be sure to pay attention to its length. The longer (or further back it extends), the better your chance of fitting the seat with minimal fiddling. The downside is you may have less room to work with if you decide to install a roll bar. Since that’s in the works for me, I purposely went with the BW’s smaller footprint version.

Sliders
Most race shops will recommend avoiding sliders since they introduce a potential failure point. However, that may not be an option on a street car, so you just need to look for a high quality set withc features such as durable construction, double-locking mechanism, and ECE R17 (European crash standard) ratings.

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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.

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Installation

Tools and Hardware
I’m not going to lie, seat install on this car is one of the most annoying mods. 95% of the annoyance is due to the required trial and error of what you’ll learn along the way; the other 5% is not having the right tools. So I’ll try to document the key findings so your install is way more straightforward.

As for tools, you’ll need a cordless 1/4 ratchet with hex sockets, 1/2 socket with extension, 16mm socket, metric wrench set and metric carbide drill bits. FYI most seats and brackets come with hardware but it won’t hurt to have spare m8x1.25 socket head screw of varying lengths (16-25mm), m8 fender washers and nylon lock nuts.

Assembly
There’s plenty of DIY write ups on how to remove the factory seat so I’m only going to focus on the bucket seat install.

The key to simplifying the install is pre-assembling the brackets and seats first to ensure all the brackets line up and any required drilling is done beforehand. Once you’re confirmed that, disassemble the hardware and do the same thing for slider and floor mount. Depending on floor mount, some extend further behind the floor pan bolt whereas others end right around there. This is why you want to confirm your slider actually bolts in because there could be a scenario where the pre-designated holes on slider don’t line up with floor mount, which means you’ll have to drill a new hole in your slider rails.

But once you’ve confirmed a) side mounts, brackets and sliders align and b) sliders align with floor mounts, you can now proceed with install. Just make mental note which threaded hole you utilized on the floor adapter.

1. Bolt down the new floor mount adapters but don’t fully torque down.
2. Pre-assemble sliders and mounts to seats. Also use this time to mount the factory belt receptacle to which every bracket you went with. I had few m10 nylon lock nuts handy to secure them to my brackets.
3. Move both sliders forward just enough so you see the back holes since you’ll want to secure those first based on the pre-assembly fitment you did before.
4. Place the assembled seat on the floor mount. The goal should be to get rid the slider mounted furthest inboard (i.e., toward transmission tunnel) and furthest back (i.e., toward the bulkhead) as possible.
5. With the rear holes of slider exposed, mount the inner rail first. Then move the slider back and secure the front hole of the inner rail. Even though you are working on the inner slider first, make sure you move both sliders in parallel.
6. If you have trouble securing the inner rail because the seat rubs against trans tunnel, pull the seat out and try using an aluminum shim or spacer on the side mount to offset the seat slightly away from the transmission tunnel. Some side mounts have offset designs to begin with it offer lateral adjustability for this very reason.
7. Once the inner rail is mounted down, do the same for the outer slider.You want to use the most inner ’column’ of threaded holes on the floor mount. If the outer side mount is too far extended from the seat, use a thick spacer or shim to close the distance.
8. Bolt everything down, use loctite as necessary and fender washers where possible.
9. Mount the factory belt and route accordingly, test to make sure seat is secure, sliders engage smoothly without any binding and seat shoulders clear door cards.

Pics to follow but here’s a quick picture of passenger side.

[amcp]

Great post and the seats look perfect. Thinking about a set for my M as well.

[MBan]

Did you weigh the components going in and those coming out? I've heard the weight advantage of aftermarket seats is not as big as expected once you've gotten everything installed.

[3002 tii]

Originally Posted by MBan

Did you weigh the components going in and those coming out? I've heard the weight advantage of aftermarket seats is not as big as expected once you've gotten everything installed.

Not yet but I can next week, but really depends. It’s true the ancillary hardware adds up but if your reference point is factory electric seats, the weight savings will be substantial. I was able to take the fully assembled bucket seat in/out multiple times with ease, whereas the factory seat would take more effort.

But weight saving aside, the biggest benefit is the side support and ability to run harnesses. Being strapped down and not sliding around helps immensely with lap times.

[Beedub]

Great post, really informative.

i went for the tillet carbon seats for weight ( massive massive saving over stock and that includes the hardware as well ) side mounted setup with siders too for ease of use. the seats are way way more comfortable than they would appear and can be driven in for hours on hours. The tillet is a extremely expensive option but the quality is GT3 Rs worthy ( the resins do kinda stink however, lol) and the support they offer is NUTS. Whats really cool is the lower seat is like a bowl so your sat super low and the seat is molded in a slight reclined position which extends your feel out in-front of you, difficult to describe but by far one of the best seating position Ive enjoyed. I used all the stock components such as seat belt reciprocals, tensioners , etc for an oem type finish. No wiring cut, all premade harnesses for a plug and play setup. combined with the Deep dish MOMO model 07 steering wheel the driver zone in this car feels so special. Setting it all up for the drive was a REAL pain and took weeks to get right, the passenger seat went in perfect on the second hit ( iv got it set slightly lower than the drivers seat , passengers always comment how cool it feels sat on the floor, lol). If you havent already i really recommend a proper steering wheel setup to get the most from your seat, the thinner rim just brims with feel and makes an already excellent rack feel so much more alive!

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Originally Posted by Beedub

Great post, really informative.

i went for the tillet carbon seats for weight ( massive massive saving over stock and that includes the hardware as well ) side mounted setup with siders too for ease of use. the seats are way way more comfortable than they would appear and can be driven in for hours on hours. The tillet is a extremely expensive option but the quality is GT3 Rs worthy ( the resins do kinda stink however, lol) and the support they offer is NUTS. Whats really cool is the lower seat is like a bowl so your sat super low and the seat is molded in a slight reclined position which extends your feel out in-front of you, difficult to describe but by far one of the best seating position Ive enjoyed. I used all the stock components such as seat belt reciprocals, tensioners , etc for an oem type finish. No wiring cut, all premade harnesses for a plug and play setup. combined with the Deep dish MOMO model 07 steering wheel the driver zone in this car feels so special. Setting it all up for the drive was a REAL pain and took weeks to get right, the passenger seat went in perfect on the second hit ( iv got it set slightly lower than the drivers seat , passengers always comment how cool it feels sat on the floor, lol). If you havent already i really recommend a proper steering wheel setup to get the most from your seat, the thinner rim just brims with feel and makes an already excellent rack feel so much more alive!

Those seats are amazing. I don’t think my old lame self could deal without having cushions. But you can’t ever go wrong with carbon seats lol.

[E93Seattle (Racerbruce)]

3002 tii -
amazing - well done.

your definitive detail and description of this conversion is incredible.

"little" things like ensure if you have sliding/adjustable seats that they meet the EU requirement.

so well done.

[Beedub]

Originally Posted by 3002 tii

Those seats are amazing. I don’t think my old lame self could deal without having cushions. But you can’t ever go wrong with carbon seats lol.

Literally everyone says the same thing.... until they sit in the them. The way they mold to your body is pretty unreal. However their are some special order seat pads to make things alittle more comfortable , each seat came in at 4kg, lol! Fitting aftermarket seats in this car is a PITA as you know. The pedals are offset slightly so it takes some serious fiddling!

One of the best mods we can do to this car as i find the stock seats just completely junk for back road thrashes!

[amcp]

My worry regarding the Tillet seats is the lack of a headrest. If you were in an accident on the road, smacking your head on CF probably sucks a bunch.

[Beedub]

Originally Posted by amcp

My worry regarding the Tillet seats is the lack of a headrest. If you were in an accident on the road, smacking your head on CF probably sucks a bunch.

once your in the seat your head rests against the tillet pad you see in the pic.... it couldn't hit anywhere , not sure what you mean tbh.....

[amcp]

In an accident your head will bounce around. IE rear ended or front end collision.
That pad doesn't look very stout compared to the Sparco or OEM seat.