Racing Seats and removing pretensioners the correct way without disabiling SRS System

[thegenius46m]

As the title states I am looking to remove to remove the pretensioners from my m3 and run rear buckles with some modifications like the S2K community runs with a fixed length rear buckle so the belt no longer has to go over the side bolster on my recaro pole position. Since this is an FIA racing seat and not a street bucket you can’t run the pretensioner properly through the pass through on the side like many of you know. This is sketch in an accident because you could in theory submarine.

Running a rear buckle will get the belt at a proper angle and of the two situations at least this will be holding you in the seat properly so when you fly forward the upper tensioner on the b pillar will still lock the entire seatbelt from letting you fly forward. Currently with the buckle going OVER the seat the buckle pretensioner is kinda worthless.





Now the dangerous way everyone runs these on the street because the seat is truly designed for harnesses only:




Now I want to get rid of the pretensioner buckle entirely and I know how to code everything out BUT I’m fairly certain that will just get rid of the faults for the missing hardware. What I’m not sure is whether it will truly disable the SRS system in an accident by missing the pretensioner buckle?

It appears there is a seat belt sensor in the buckle that tells the SRS system when a person is sitting in the car and buckled in so when there is an accident the airbags do indeed go off. If I remove the pretensioner that obviously would no longer be present.

I haven’t dug into the logic just yet but being a safety thing I’d like more assurance the front airbags will still go off in a front impact if I can tell the airbag system to ignore the presence of the pretensioner being a requirement? I’m not sure that’s possible but will be taking a look tonight.

Worst case I guess I could keep the pretensioner buckle hard mounted with a buckle permanently connected then run the rear buckle mounted but that’s ugly.

Curious if anyone has done this properly?




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[SpaceJockey]

I am dealing with the same thing. What rear buckle are you going to run?

[thegenius46m]

I am dealing with the same thing. What rear buckle are you going to run?

So there's a whole list of parts you can run from schroth that I'll link here if I end up doing this. Basically you run a stock rear buckle, a a 3 bar slide and a belt with an eyelet and bolt it to the seat like this




The point of the 3 bar slide is so that the buckle is a fixed length that you will preset so that the buckle has nowhere to go in an accident and will keep proper tension then the b pillar tensioner on the regular seatbelt will do the rest.

S2k runs a similar setup from the factory and I saw my buddy's car last night and this seems way safer than what I'm running now which is buckle over the seat. On track I run a 6 pt so this never mattered but now I'm older and a little wiser and didn't realize till last night there truly was a much more viable option.

Let's be honest here guys… unless you get one of the non fia seats that are huge you're not going to be able to use the stock buckle pretensioner how it was designed in the first place so it's not really doing its job in an accident anyways. Plus it seems it's more of a redundancy for extra lock in an accident since you still have the main one on the b pillar one that grabs the entire belt from moving. At least with this modification, the seatbelt will be properly around your waist instead of halfway so there's no way you're going to submarine


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[George Hill]

This has been in the back of my mind as well, I always give people the caveat you may submarine with the belt going over the bolster like you depicted.

Right now I am working on mounting a convertible E46 rear seat belt which is very short and in some situations will allow the belt to connect through the hole in the side. But I'd like to change it a little bit so thats on my to do list. I'll get some pics later today.

[zivagolee]

I run the PP ABE and I have my buckle going through the hole in the side.

[OEM3]

I have the factory assembly under the seat, covered by black towels. Inserted a tongue into the buckle so the SRS system doesn't think my seatbelt isn't fastened (I NEVER start my car before buckling up).
The pretensioner is unplugged, used a resistor to trick the system into thinking that it isn't.

[usdmej]

Now the dangerous way everyone runs these on the street because the seat is truly designed for harnesses only:

yes it's not ideal, but at the same time i haven't seen any anecdotal information about it actually happening

porsche carerra GT came like that stock



996 gt3 also came like that, albeit without pretensioners

[thegenius46m]

I have the factory assembly under the seat, covered by black towels. Inserted a tongue into the buckle so the SRS system doesn't think my seatbelt isn't fastened (I NEVER start my car before buckling up).
The pretensioner is unplugged, used a resistor to trick the system into thinking that it isn't.

Yeah I didn't want to do this but given it's a safety thing and I really don't want to play the guessing game with my life in an accident I don't think coding out the missing parameters of hardware that isn't present will for sure allow the system to trigger the airbags in an accident so I think this might be the only real option here which would be to keep the pretensioner under the seat with a spare buckle always plugged in so the car always thinks someone is in the seat. This is what I've been leaning towards for the last 24hrs now. It's the safest bet to ensure less issues but it's a little ugly.

The airbags are virtually free ($50 each) to replace from a part out or junkyard in the event of an accident which honestly is my last concern. My insurance would pick that slack up anyways


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[Nate047]

Just use the 6-point and your helmet and a HANS every time you get in the car.

JK

But I would love to see a verified working way to run non ABE Pole Position or similar seats with fully functioning SRS.

[karter16]

For anyone digging into this more I recommend "ST403 Passive Safety Systems" as it gets into the detailed workings of BMWs various passive safety systems. There is a lot of detail in there (hundreds of pages) which may hold some of the answers to this discussion. I have not trawled through it all to find the answers. But flicking through it seems you would be able to find out answers around the failsafe states of the various systems, etc.

[thegenius46m]

Just use the 6-point and your helmet and a HANS every time you get in the car.

JK

But I would love to see a verified working way to run non ABE Pole Position or similar seats with fully functioning SRS.

Haha for real.

In all honestly I decided this is too risky to play guess and check with my body so I'm unfortunately going to leave the pretensioners connected with a spare buckle permanently plugged in so the car thinks someone is always in both seats so in the event of an accident both front airbags deploy as intended. Idc about the airbag cost because that's the least of my worries if there's a crash hard enough they go off lol. Then I'll run that s2k mod so I'm properly latched in.

I ordered everything on Friday so I will keep everyone posted on what the solution ends up being. I'm either going to have a friend help build a bracket so mount the pretensioners under the seat securely or I'm going to just leave them attached on the side but hidden out of the way so I don't have to deal with rattles.


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[bigjae46]

First...nice thread opening pic of your crotch...hahaha

I used a Schroth quickfit without the pre-tensioner with a racing seat before I installed the roll cage. Keep in mind I rarely ever drove the car on the street...maybe 2-4 times per month.

[thegenius46m]

First...nice thread opening pic of your crotch...hahaha

I used a Schroth quickfit without the pre-tensioner with a racing seat before I installed the roll cage. Keep in mind I rarely ever drove the car on the street...maybe 2-4 times per month.

Hahahahhaa! That's not mine but this is great.

I'm not worried about the track because I'll have a proper 6 pt with sub straps.


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