Harness Spine Compression & Seat Holes???

So I got my fixed back seat in the mail today.

I sat in it and everything is nice and snug, happy as can be. Then I reach back to feel for the harness holes. The top of the hole is about a good inch below my shoulder level. I remember reading something about spinal compression if the holes aren’t exactly at shoulder level, my question is how real is this danger? am I overreacting?

The good thing is if I take out the cushion the holes line up decently, but then again I’d be sitting on FRP the whole time which I want to avoid.

Any comments or edification will be greatly appreciated.

Thanks,

-H

An inch isn't much. I would install it as is and sit in it with your belts cinched up tight. Then see if the shoulder belts are sloped down much. I'll bet they aren't all that bad, the belts will pull you down into the seat.

Good to know.

If it was a huge issue, I was also thinking about getting some seat cushion foam from Amazon and switching them out as well. 

Such a pity, everything else about the seat fits except the damn harness holes.

The recommended SFI belt angles take spinal compression into consideration.

http://www.sfifoundation.com/wp-content/pdfs/guidelines-bulletins/Seatbelt%20Installation%20Guide%2006-05-12.pdf

-10* is optimal for shoulders. Use an inclinometer and get it as close to ideal as possible.

For what it's worth, There's practically no padding at the base of my aluminum race seat and it's totally fine.

^This. Once it lines up with the recommended belt angles, it's fine. And padding is overrated unless you're doing endurance racing.

 Thanks guys. 

I remeasured everything again and it seems like the height different is less. It’s about 1cm from the top of my shoulder to the top edge of the harness slot with the padding in place. I stuck a ruler through the slot and let it rest on my shoulder it’s definitely less than 20 degrees off horizontal. 

I’m hoping over time the cushion will naturally sag offering more clearance. And I was thinking in the event of a front end collision the top of my shoulder is soft tissue anyway so it’s compress naturally.  Well I’m hoping so anyways. I think the seat will be worth keeping. Being 6’3, I don’t have that many choices in terms of seats  

What seat? How is it mounted and what are you mounting the harness to?

You do own a HANS right?

Take out the seat cushion.  I'm all torso, to the point where I really only fit in 2 or 3 seats.  Recaro SPG XL, Racetech 4009W, Cobra Suzaka GT.  All of them have really large shoulder harness holes.  While I "fit" in a Recaro Pole Position, the shoulder harness holes are 2" below my shoulder level.

GameboyRMH said:

...And padding is overrated unless you're doing endurance racing.

...Or are involved in a wreck where significant vertical forces are involved. A Stalker driver that had a high speed off course excursion, as the result of a suspension failure leading to brake loss, spent months in a back brace due to injuries which were exacerbated by insufficient seat padding on a frame-mounted aluminum seat.

Preventing spinal compression injuries in wrecks is why many top racing sanctioning bodies now specifically require an energy absorbing seat foam to be used on at least the seat bottom.  Much like rollbar padding though, it really should be the good (firm) high energy absorbing stuff, not just the soft comfy stuff.

^ Can you link us to the requirements? This is news to me and I'm very interested (always am, safety wise).

Unfortunately I don't have access to professional racing rulebooks, but back when I reserached it I was able to find a number of secondary sources like this:

Kirkey NASCAR Seat

Kirkey Racing wrote:

SFI 45.2 certified padding in bottom of seat to pass NASCAR rules. 

Apparently a pour-in version of this SFI 45.2 foam is typically used when making higher level formula car seats. Also used in helmets, child seats, and lower level formula car seats is XPS (eXpanded PolyStyrene).  If looking to GRM it and buy similar in sheet form, this would be the white stuff made of many individual pellets, not the smooth pink/blue sheets of EPS (Extruded PolyStyrene).

In the aviation world, where vertical impacts are the norm, studies have also shown CONFOR to significantly reduce back injuries in very-hard landings. 

^ Very interesting!

Makes total sense (I work in aviation but never done impact analysis with seats).

There's no space for padding in my track car but in my future one this is another item to add. Thanks dude!

In reply to Blaise :

I'm using a Bride Zeta3 Type L which is the tall version. It's a FIA seat which is always nice. I have a weird body and where I'm kind of lanky and the seat holds me better than the recaros I've tried. Plus I'm in Korea, which makes getting them a little easier since Japan is right next door. They are mounted on their standard sliding side mount rails. 

The harness is a Schroth ASM Autocontol II 2 inch belts which has the retractor. The retractor will be mounted on the C pillar which is pretty close to horizontal. 

No HANS device yet. I don't do that much track driving yet so I couldn't justify the additional cost. If i really get into track driving I'll have to upgrade the seat and harness at some point because of the Hans. 

AH! I didn't realize they even build a 3-point replacement. Just make sure your airbag system is functional and you should be good to go!

I have same issue with my recaro spg. Couldn’t figure out why my belts wanted to slip off my Hans device constantly. Even with seat cushions out still too tall in the torso; new seat is on the list along with trying to lower the seat mount. I would like to get more space between my head and the cage. Jcamper

I'd advise you not to install a seat and harness that aren't compatible with a HANS device in 2017...it's already required for any form of wheel to wheel racing or time trial, and you shouldn't be surprised if the safety requirements soon propagate "downward" to track days (perhaps with a hybrid device).

Some track day events require anyone using a 5-6 point harness to have some form of head and neck restraint.  The devices are now cheap enough that they aren't the $800 hurdle they once were. I bought a HANS 15 years ago, I'd run out of excuses as to why I hadn't purchased one and having a family made me realize I needed to get one.  At the time the company I'd worked for closed down and my new employer didn't pay very well so I worked some Kart races over the summer to pay for it. 

Before I put seat pour material in my aluminum seat I put one of my old motorcycle back braces on the seat back (cheaper impact foam one not my  Dainese spine one) and SFI impact foam in the base.

I struggle with seats as well 5' 7" with 30" inseam and weigh 140lbs. In my single seat cars I have to pour a seat, I didn't on my first one (Formula Vee) and would end up bruised just from driving it. In production cars I prefer the aluminum seat with poured foam because I can get my torso at the right height for the shoulder belts. It also allows me to get the anti submarine belt in the correct spot. The aluminum seat in my Datsun didn't have a slot in the base for the sub belt, which is fine because of my size I need to cut the hole specifically to me for the belt to fit correctly. I try to treat seats like helmets as far as fit goes.

Digging up an old topic but my question is related. I just picked up a set of FIA rated seats for my track/fun car (1984 525i) to go along with the bolt in roll bar I've built and harnesses. I'm 6'3" and the seats fit me perfect but for anyone with a shorter torso the shoulder harness holes sit a couple of inches too high. Is this a big issue? There won't be spine compression issues that I can see but the effectiveness of the shoulder belts might be compromised. The bottom pads for the seats are just velcroed in so I could make a booster to go under the padding to get the passengers (or drivers) up a bit but obviously they won't be as deep in the buckets then. Any recommendations for something lightweight to make that booster out of are appreciated. Seats are Bimarco Futuras, I'm 6'3" but my height is all in my legs so probable someone 6' with average proportions would be the ideal fit in the seats.

Thanks,

Adam