Harnesses with stock seats

Let's get this out of the way: it's a bad idea. I know.

But let's just take "unmodified stock seat" as a given. What's the least bad way to run the sub belt? Anchoring it is not an issue. The car is a 2004 Miata with a roll bar.

I thought YOU were the guy with all of the answers about The Answer.

With a 6-point you could just run the subs from the lap belt anchors.

Assuming cutting a hole in the seat base isn't really an option? What about the Schroth ASM harness?

I've used the seat anchors in the front. The most important thing for the anti-sub belt is to keep the belt on your hips more than you going down.

I'm sure there are better places, but I was pretty confident when it was all tight.

Anchoring the sub is not an issue. We're using a 5 point, and we can put an eyebolt wherever we need it along the floor.

I'm more interesting in routing - do I go over the front of the seat or the back? I seem to recall reading that the latter was preferred as it will tighten as you move forward instead of loosening, although it seems a little hard on the family jewels.

Cutting a hole in the seat is not acceptable to the car owner. I know we're not dealing with the best option, I'm looking for the least bad one.

Common sense (at least my version of it) tells me to anchor the sub belt directly under the trailing edge of the seat bottom, then route the belt between the bottom and back of the seat. That should give you the shortest, least-influenced-by-seat-deformation routing, which I think is the best you could hope for. I think you have to assume the seat will act like jello in a crash, and let the belts move in whatever direction they are tugged in.

Seriously though, the dude should buy a real seat.

I discovered yesterday that the people who run the mile events require a 5 point harness but allow stock seats.

Personally I have a 5-point with the sub strap mounted directly below the front of the seat. A combination of the seat giving way and a reclined driving position mean the sub strap can do its job of anchoring the latch down so the shoulder straps don't yank it up to get friendly with my liver. I like the harness tight enough that breathing is difficult.

I have heard that the way to run a 6 point is to anchor the sub straps at the same place as the lap belts. Must be for people who can sit upright while driving...

I know the original question was about the sub belt, but if this is for a stock Miata seat what's keeping the shoulder belts from separating and allowing the driver to chew the steering wheel? There are no holes for the shoulder straps and it has an integrated headrest. That's a no-no for multi-point belts.

Yeah, IMHO there really is no acceptable solution for harnesses with stock Miata seats.

On my dad's old Miata, he cut a hole in the seat pan, put some sort of trim around it to take care of the sharp edge and sewed a "sock" into the seat cushion so that the sub belt could be run through the seat bottom at the proper angle. It's a little extra work, but worth it if you ever crash.

I have modified a stock seat base in the past to take a sub belt. But I was told "no" by this customer on both using a race seat (my first choice) and modifying the stock seat.

You could use a sternum strap to get around the shoulder belt problem. Makes them a bit more of a hassle to use, but it should be a reasonable option.

Maybe I'll just hand him the harnesses in a box and say "here, you do it".

I did find a Simpson installation page that showed the shoulder belts crossed behind the headrest. Still looked wonky to me.

I would probably just not do theinstallation then Keith. You know this, but the customer needs to realize that saftey is no place to cut corners.

DeadSkunk wrote: I did find a Simpson installation page that showed the shoulder belts crossed behind the headrest. Still looked wonky to me.

Actually, I've done that with a stock seat and a harness bar in the past. It actually works pretty well to keep the belts from moving apart on the bar, but I never tested it in a crash.

My recommendation to the boss is that we install the harness mounting points (easy enough) and let him clip the harnesses in and route them however he wants. Frustratingly, the customer is a Spec Miata racer so he should also know better. But he wants to turn this 2004 street car into a track car without compromising the street use, thus the stock seats.

Considering the business you are in, this is the only acceptable solution:

Keith Tanner wrote: Maybe I'll just hand him the harnesses in a box and say "here, you do it".

Anything else will put the liability for the improper installation completely on you.

You know it's wrong. You've said so here. Better not do it.

Our business in general is a liability nightmare.

I figured there was a good chance I'd get more preaching than tech help.

SVreX wrote: Considering the business you are in, this is the only acceptable solution:

Keith Tanner wrote: Maybe I'll just hand him the harnesses in a box and say "here, you do it".

Anything else will put the liability for the improper installation completely on you. You know it's wrong. You've said so here. Better not do it.

+1

Keith Tanner wrote: Our business in general is a liability nightmare. I figured there was a good chance I'd get more preaching than tech help.

I think you've gotten both.

You are asking the best wrong way to do it. You got that answer.

I have no interest in preaching to you. Just reminding you of the stuff you already know.

Sometimes you gotta tell people "No" Keith. This is definitely one of the instances. He's a racer, he knows. Just tell him you value his continued business and don't feel right doing something you know will compromise his safety.

You're right, the preaching comment was out of line. Although this is the same forum where people occasionally rant on about having to buy a new helmet every decade I still don't think we've got a solid answer on if the sub belt should go over the front or the rear of the seat if there's no hole available - which is the case in some race seats as well, I can think of a Sparco that's like that.

This particular customer has a personal relationship with the company, especially with the boss. So the big man's going to tell the customer that he has to man up and get a real seat, or stick with the stock belts.

Which brings up an interesting question that's more theoretical. Would a set of five point FIA harnesses, not ideally installed with a stock seat, be more or less safe than a set of 10 year old stock three point retractable belts?

Kind of doesn't matter. In court, the installer of the 5 point would be liable, but the installer of the 3 point (manufacturer) would not.

I don't think your question can be answered, because I don't think the primary risk is the age of the belt or the number of attachment points. The primary risk is the specific routing of the belts in relation to the specific nature of the incident. In many scenarios, the 5 point would perform better. But in a sideways slide into the wall, or a rollover or T-bone, all bets are off.

Considering that most race cars have had their airbags disabled, may have modified the collapsible steering, and may have compromised the crumble zone with the cage, the reality is that the 3 point has been compromised too, since the entire package of safety system devices as designed from the factory to work in conjunction with each other is not in place. (Not that it matters, from a liability standpoint).

Personally, I'd rather the 5 point, and I have had them in a car with stock seats. But I installed them myself, and wouldn't ask you to do it.

If it were me, I'd take a 5 point with the crotch strap over the front and crossed shoulder belts over the stock 3 point belt. I've crashed a race car a couple of times, so I have some idea about what went on.

I'd put in the mounts, tell him that he really needs to use a different seat (which doesn't have to be a 'race' seat, there are some very nice reclining aftermarket seats with harness cutouts) and hand him the belts in a box. I personally don't see anyone who is unwilling to remove the stock seat being happy with the belt running between the bottom and the back. They're looking for compromise, not the safest solution,and that means mounting the 5th point right at the seat edge and accepting that it's more of a catchers mitt than a harness.

I'm actually kinda surprised that no one makes an anti-sub belt that attaches both at the front and rear of the seat bottom, kinda wrapping around it if you will, for just this situation. Six point could be a sewn assembly like a tow dolly wheel strap rig, one ring in the front and two in the back, with a couple straps.

Might have to break out the upholstery sewing machine and see how it would work...