guitarman376

Hi guys, essentially I am wondering this: In the photo (link below) I see the acceptable mounting position/angle of the harness which goes over the shoulders.

https://www.google.com/searchq=shoul...ml%3B650%3B420

Generally I have read that positive angle is better than negative and that the most negative you want is 10 degrees. Here is the problem: The fiero seats I am going to use have optional shoulder harness slots, but only in one place, which happens to be below my shoulders by a good bit. I'm 6'4, hence the low-mounting fiero seats.

Is it just the angle from the harness mount on cage to the shoulders that matters? Or is all geometry out the window if the seatbelt slots in seat are too low relative to my shoulders? Another way of saying this is would it be safe to have the harness bar mounting in the acceptable safe range (relative to my shoulders) but then to have the harnesses go through slots and back up (at a sharp angle) 4" to my shoulders?

This is making me reconsider my later plans of getting 4 point harnesses and instead make a good retractable 3 point system once cage is installed. I will try and read up some more. TIA

bop11

Are you planning on racing this vehicle or driving around Boston? Where did you get this information? Anything that will keep you from crashing into the steering wheel and windshield is an improvement. There is no real crush zone in that car, so plan for the minor accident and drive safely. Put the harness in where it fits best and realize that at your height you will probably can't get your feet under the steering wheel anyway so your knee's will hit you in the chest.
Don't agonize over it and drive defensively.

ajzride

The best option is to mount the seatbelt to the roof, and ignore the shoulder belt slot in the seat. I've been down this road with my S2000 seats. Buy a set of shoulder belts which have a built in sash, this will lower the pivot point and get the angle correct. You can find how long a sash you need by mocking up the seatbelt with some cardboard strips.

Here is the set I bought, with the 8" sash (I'm 6'1").



http://wescoperformance.stores.yahoo.net/resebe.html

3 Point Retractable Seat Belts with Long Sash Guide

guitarman376

I noticed the link doesn't work, sorry about that. I was referring to a 4pt or 5pt racing harness, specifically the part of the harness that goes over your shoulders.

I understand that the mount for this part of the harness has a safe rangle of angles for mounting relative to drivers shoulders. This is such a specific question I did some pictures to show what I mean. In the first is with everything ideal (aka shoulder harness slots are right at shoulder height).

In the second picture is the situation I have. I was wondering if this nixes all the geometry meant to keep a person safe. I know a poorly mounted harness is very dangerous in collisions, but I don't know if my situation is breaking 'the rules' or whatever.

guitarman376

Now that the photos hopefully give you guys an idea what I am talking about, does having the harness go like the in 2nd picture still crush my spine in an accident? My intuition is telling me yes since the seat itself would compress me.

guitarman376

No one has input on this? I decided I am going to go ahead and have the harness slots put in the seat regardless. Has to be better than no shoulder restraints...

bop11

From a mechanical engineering stand point, (40 years), I think that if you do #2 what will happen is that the loop in the seat will actually rip the top of the seat. If this happens it would give excess length to the belt which would let you go forward into the dash and not securely hold you back. The upward force on the seat would be your weight times the deceleration trying to straighten the belt, not crush your spine as the seat is only wire and light gauge steel. The first system would restrain your movement much better.

guitarman376

Thanks bop11, I am going to try modifying the headrest to make my own slots I think.

dcohen

The problem with having the seat belt below your shoulders is that in the event of a crash the seat belt could potentially pull in a direction that would put an axial load on your spine. Think of a ratchet strap going over a box to hold it down to a trailer. The ratchet strap is pulling straight down on the box.

Axial loads on the spine are the worst kind and cause the most severe spinal injuries. Not something I would what to take a chance on.

guitarman376

Yea I am on the same page. That is why I am going to try to figure out how to add harness slots higher up on the headrest instead of the crease they are normally made in.