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      11-08-2010, 04:52 PM   #1
sipman
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seatbelt harness on M

I was wondering this weekend about a 4 or 5 point seat belt harness on my z4mc. I noticed the seats have seat belt guides on the outside to guide the shoulder strap. Anyone know if we can add the passenger seat belt guide to the driver's side chair, allowing the shoulder straps of a 4 point harness to fit in there?
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      11-08-2010, 04:58 PM   #2
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Originally Posted by sipman View Post
I was wondering this weekend about a 4 or 5 point seat belt harness on my z4mc. I noticed the seats have seat belt guides on the outside to guide the shoulder strap. Anyone know if we can add the passenger seat belt guide to the driver's side chair, allowing the shoulder straps of a 4 point harness to fit in there?
U need a harness bar or a half cage to use shoulder belts... No one makes a harness bar for our cars, so you would have to get one custom made.

I don't even know if you could use a harness system with the stock seats anyway. I'd bet not, but I could be wrong.

Look at me being the race seat / belt install guy today ! hahaha
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      11-08-2010, 05:04 PM   #3
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You CANNOT use harnesses with the stock seats, and you CANNOT use harnesses without a roll cage, unless you want to die.
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      11-08-2010, 05:07 PM   #4
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You CANNOT use harnesses with the stock seats, and you CANNOT use harnesses without a roll cage, unless you want to die.
Because dying SUCKS.
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      11-08-2010, 09:06 PM   #5
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      11-08-2010, 09:40 PM   #6
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Don't take this as a challenge. It's not. But why can't you use them with stock seats? What would make them more dangerous than the stock 3 point belt?
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      11-08-2010, 09:43 PM   #7
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Don't take this as a challenge. It's not. But why can't you use them with stock seats? What would make them more dangerous than the stock 3 point belt?
3 point belt crosses you, 4 point doesn't. 4 point with stock seat = belts will just slide apart and you will go flying forward as if you had no belts. 4 and 5 points have to be held in place.
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      11-08-2010, 10:05 PM   #8
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I'm definitely not completely thought out, right now. In my minds eye, I was seeing the stock seat, with the original seat belt guide, plus an additional seat belt guide retrofitted from the passenger seat, on the inboard portion of the backrest. This would then guide the two shoulder belts like the cutouts in some racing seats. The harness would then be connected to the body or to a chassis bracing. With the retractable tray out of the way, the harness could be mounted to a chassis brace or to the chassis itself in the trunk.
Would this still not satisfy a safe installation?
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      11-08-2010, 11:31 PM   #9
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All kidding aside....They're not designed this way for a reason.

A racing seat is specially designed for the harnesses to hold you back directly from behind, at your exact shoulder height as well. If the straps are mounted higher than your shoulders, it will drive your body down in an impact. This is also why a 5 point is better than 4 point as well, so you have the anti-sub strap to help stop this. You can't use one with the stock seat.

The way you are describing your idea would have the shoulder straps bending around the seat, instead of holding you back from directly behind your body. Seems like your body would just pop out forward easily between the straps in an impact.

The lap portion must also be anchored at a specific angle to your hips as well. I doubt that mounting to a stock seat would give you this perfect geometry needed either.

Another issue, even if you had a racing seat and the harness mounted perfectly, is the lack of a roll bar. If you rolled your car bad enough and you were strapped into the seat with a 4 or 5 point, you would crush your head and break your neck, as a 3 point strap will let your body move in towards the center of the car. The 4/5 point harness wouldn't let you move at all.

Are you willing to risk your life on a cobbled together seat and set up ? Not really something I would risk.
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      11-09-2010, 09:12 AM   #10
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Quote:
Originally Posted by sipman View Post
I'm definitely not completely thought out, right now. In my minds eye, I was seeing the stock seat, with the original seat belt guide, plus an additional seat belt guide retrofitted from the passenger seat, on the inboard portion of the backrest. This would then guide the two shoulder belts like the cutouts in some racing seats. The harness would then be connected to the body or to a chassis bracing. With the retractable tray out of the way, the harness could be mounted to a chassis brace or to the chassis itself in the trunk.
Would this still not satisfy a safe installation?
I knew exactly what you had in mind, no it won't work, you will die.
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