6-point harness installation in miata

[ferris]

I know a lot of you have 5/6-point harnesses and I wanted to know what mounting points you used.

I plan on using the left side lap belt for the left lap belt, the right tunnel mount for the seat for the right lap belt, obviously the roll bar for the shoulder harnesses, and then maybe the rear seat floor mounts for the anti-sub belts. I am not sure if this mounting will give me the correct angle or not, but it is the only place I can think of using.


Also, does anyone use the stock belts (Dave, I think you might have this still in your car) because I have no idea where to mount the buckle. I rather not drive to an from events with a neck collar and helmet.

[milkmandan]

Drill holes in the floor and use backing plates. It's the safest way. Just don't drill through your brake lines. You can use the same mounting points for the lap and sub belts (if you're using 6pts), just about under your butt will give you the correct angle on all 4 of your belts.

[ferris]

I thought the lap belts should be outside of the seat, not under the seat, similar to the current lap belt on the stock seat.

The backing plate is a great idea for the subbelts (I am using a 6-point harness).

[kyle.bowker]

What seats do you have? Are you using factory sliders still? The OEM seat mounting bolts are not long enough to be able to mount the harnesses and hold the seat. Plus the sub straps won't be positioned correctly if mounted there. Alternatively, if you're running a custom fabricated bracket for a racing seat (side mount or bottom mount) it may be possible to incorporate a sturdy mount that is part of the seat bracket and helps distribute the load over a wider area but much depends on how well your seat bracket is engineered and fabricated and the method by which it is attached to the floor (OEM mounts or custom mounts with backing plates). It's probably easiest to just drill some holes in your floorboard and mount eyelets with beefy reinforcing plates top and bottom.

[milkmandan]

From the SCCA GCR Section 9.3.19

C. The shoulder harness shall be the over the shoulder type. There
shall be a single release common to the seat belt and shoulder
harness. When mounting belts and harnesses it is recommended
that they be kept as short as reasonably possible to minimize
stretch when loaded in an accident.

The shoulder harness shall be mounted behind the driver and
supported above a line drawn downward from the shoulder point
at an angle of 20 degrees with the horizontal. The seat itself, or
anything added only to the seat shall not be considered a suitable
guide. Guides must be a part of the roll cage or a part of the car
structure.

Only separate shoulder straps are permitted. (“Y” type shoulder
straps are not allowed.) “H” type configuration is allowed.

D. The single anti-submarine strap of the 5 point system shall be
attached to the floor structure and have a metal to metal connection
with the single release common to the seat belt and shoulder
harness.

E. The double leg straps of the 6 point or 7 point system may be
attached to the floor as above for the 5 point system or be attached
to the seat belt so that the driver sits on them, passing them up
between his legs and attaching either to the single release common
to the seat belt and shoulder harness or attaching to the shoulder
harness straps. It is also permissible for the leg straps to be secured
at a point common to the seat belt attachment to the structure,
passing under the driver and up between his legs to the seat belt
release or shoulder harness straps.

All straps shall be free to run through intermediate loops or clamps/
buckles.

F. Each seat (lap) and shoulder belt of the harness (5, 6, or 7 points)
shall have an individual mounting point (i.e. 2 for seat belt and 2
for shoulder belt minimum). 6 or 7 point system anti-submarine
straps may share a mounting point with one or both seat (lap)
belt(s). The minimum acceptable bolts used in the mounting of all
belts and harnesses is SAE Grade 5. Where possible, seat belt,
shoulder harness, and anti submarine strap(s) should be mounted
to the roll structure or frame of the car. Where this is not possible,
large diameter mounting washers or equivalent should be used to
spread the load. Bolting through aluminum floor panels, etc., is not
acceptable.

http://www.scca.com/contentpage.aspx?content=44

[milkmandan]

Schroth has a pretty good guide on harness mounting too:

http://www.schrothracing.com/sdocs/2009 ... ctions.pdf

[ferris]

What seats do you have? Are you using factory sliders still? The OEM seat mounting bolts are not long enough to be able to mount the harnesses and hold the seat. Plus the sub straps won't be positioned correctly if mounted there. Alternatively, if you're running a custom fabricated bracket for a racing seat (side mount or bottom mount) it may be possible to incorporate a sturdy mount that is part of the seat bracket and helps distribute the load over a wider area but much depends on how well your seat bracket is engineered and fabricated and the method by which it is attached to the floor (OEM mounts or custom mounts with backing plates). It's probably easiest to just drill some holes in your floorboard and mount eyelets with beefy reinforcing plates top and bottom.

I have an OMP seat (it is made in 95 so its not a current model) and I have a bracket that is identicle to this (except home made) http://www.good-win-racing.com/Mazda-Pe ... d=RcuX4v3B

The OMP side mounts mount to the homemade bracket that mounts to the factory mounting points.

I could probably make another cross member for the sub belts to bolt to and weld that into the existing bracket that I have. It might be easier to drill a couple holes in the floor and brackets to bolt the sub belts though.

[david.valeri]

I can't remember where mine mount. The car is in Ed's shop and I won't see it for another couple weeks, but I think that the lap belts mount to the OE mounting points and the sub belts are mounted through the floor with reinforcement plates. Piper Motorsports did the work so whatever they did is likely considered "correct". If anyone at the shop wants to take a photo for you I have no problem with them poking around in the car.

I have the OE belts in the car simply to pass inspection. With the roll bar in place they work for crap and don't retract properly. In their current state, I feel that the harness is safer. I also have an aftermarket steering wheel so I won't use the OE belt with the built-in "give" zone.

[ferris]

Dave,

Thanks for the help. Do you remember where the stock buckle is mounted. I am assuming they look for that at inspection as well. I was thinking that there is no way that the stock seatbelt will work with the new seat. The lap belt will be way above my pelvis with the side bolster and if I route it though the lap belt slot the shoulder belt will be very wrong. I guess I will have to drive to the track with a collar and hope no one hits me ... but as Mike told me ... pray no one hits you no matter what seatbelt you are using in that car.

I guess for inspection I could just mount the buckle to the tunnel next to the seat and never use it since the geometry will be so off now anyway.

[kyle.bowker]

My OEM 3-point seatbelt fit just fine when I had the OMP WRC and now with the Sparco Evo2+ but then again I'm a fat ass and you're a skinny guy. On the OMP seat I routed the lap belt through the outboard harness slot and over the top of the bolster to the buckle receiver. The shoulder harness was routed over top of the shoulder wing.

The challenges you face are familiar to anyone who has tried to turn a street car into a race type car. The compromise for dual-purpose is a tough one. Go with the racing harnesses and you'll be relatively safe. In MD you don't have to worry about annual safety inspections so keeping the 3-point belts isn't critical in your case.