Using harnesses on OEM Sport seats - is it possible and safe

Post Wed May 06, 2009 12:23 am

Hi there all, my E30 is currently undergoing the transformation from standard 'SE' spec coupe to become a very capable track car. The main difference between mine and most of yours is that I am keeping mine as my daily.

I am enjoying the car so much that I decided to make all the chassis modifications as originally planned but instead of stripping and caging the interior I have instead swapped the original 'SE' interior for an MTECII 'Sport' interior.

I do not want to use harnesses all the time but wondered if it is possible to install them for trackdays to work safely with the OEM 'Sport' seats? Would I mount them into where the rears are bolted? I'm assuming a 4-point harness would work ok?

Any help or advice would be greatly appreciated...

James.

Post Wed May 06, 2009 10:10 am

Hi James,

In the event of an accident, the general idea is that you are sandwiched between the seat and the harness. There is no point to having a strong racing harness in your car if the OEM Sport seat isn't equally as strong.

You would be ill advised to use a four or five point harness with anything else other than a single piece (bucket) FIA approved (Sparco or Recaro, for example) racing seat. OEM "sport" seats have a habit of breaking at the pivot point (where the bum-rest meets the back-rest) and you go sliding head first into the backseat/cage/boot and snap your neck (in the event of you being rear ended by someone at speed) or you slide forwards under the harness feet-first into the pedals (in the event that you rear ended someone or something else)

Around the world, FIA approved equipment (race-suits, helmets, seats, gloves etc) are slowly becoming mandatory, even within minor events, not because of the necessity for high quality FIA approved equipment, but because of the influx of cheap shitty low quality race gear from unscrupulous manufacturers.

Regards,
Geoff

Post Wed May 06, 2009 12:53 pm

why dose this not hapen with a standard seat belt. i would be less blunt but im in a rush. sorry

Post Wed May 06, 2009 1:07 pm

Oh, it most certainly does. In fact it happened to me personally once, but that's another story.

It is however more likely to happen with a full harness over a "normal" type seat because two of the straps go over the top (shoulder) of the seat, which exert a substantial bending moment on the seat pivot in the event of an accident. There is very little give/stretch in the harness belts, which are designed to be tighened up with you sitting in the seat.

Post Wed May 06, 2009 1:21 pm

Is it the hindg that fales? I ask as I run a 3 point on my is drivers seat. I wos in a crash on moterway on harnises once and have felt safer since.

Could I weld in strength?

Post Wed May 06, 2009 2:03 pm

Yeh, it's the hinge/pivot that fails. Usually if someone shunts you hard from behind and the weight of your body (times the number g's you are pulling) pushes back hard into the seat, breaking the hinge. That's why racing seats are one piece bucket type.

If you wan't to use a full harness in a road car, best fit a good quality one-piece bucket seat to go with it. Also, you need a good solid connection between the seat and the floor, otherwise the next thing to fail is the seat mounting - and then the harness has to hold you and the seat in place

Post Wed May 06, 2009 2:12 pm

Geoff you make some good points....on most threads actually.

I am a skinny fucker and weigh 65 kilos ish I think. My bucket seat weighs 15kilos roughly, possibly less. So the harness has to stop 80kilos if the seat mounts fail(this is theoretical, I hope they won't).

Is there any difference between a harness that has to stop an 80 kilo man and a 65 kilo man and a 15 kilo bucket seat. I was never that good at phsyics you see!

I don't think there is.

I can see the potential for problem as the bucket seat could move around underneath you I guess, but even that should be limited by the harness presuming the shunt isn't massive enough to stretch the belts.

Post Wed May 06, 2009 2:29 pm

Is your bucket seat made from cast iron Jon?

Post Wed May 06, 2009 2:31 pm

Yeah, I think i might have got confused with the standard 205 seat.

It doesn't take much.

Post Wed May 06, 2009 2:43 pm

Thanks Jon, I try my best. I really should get out of here, this damn forum thing is gettin' addictive.

If your harness is FIA approved it should have a static load failure value of well over a ton (1000kg) if I am not mistaken, possibly in excess of 2 tons. This is because the load it has to sustain in the event of a crash (for very short duration mind you), is your weight multiplied by the number of g's of acceleration you are experiencing. IE, if you experience 15g (that's a pretty solid head-on collision), say, your harness will have to hold back 975kg! Assuming your guts don't turn to jelly, you might possibly survive.

However, if your seat is on rails, and they fail, the harness will have to hold back 1200kg (heavy seat that?). This is not the real problem, however. The biggest problem is that if the seat tips, you could slide out from under your harness). This is how a lot of foot and ankle injuries occur - sharp little buggers those pedals! A five-point harness helps prevent this. A strong connection between your seat and the floor (or frame if possible) is very wise. You'll notice that there is not one single FIA approved race seat that is sold with a pair of floor mounting sliders!

Your weight, by the way, is to your advantage since the load on your body while cornering is your weight multiplied by your lateral acceleration, and is thus less for you. Similarly your forwards load while heavy braking.

Post Wed May 06, 2009 2:55 pm

'Arr' its G force that has to multiplied by the weight. I knew it was something, its been a while since I did GSCE science.

Agreed about the seat tipping. Are harnesses approved to a certain 'weighting' then? I think I made a mistake about my seat, its a shit Corbeau Forza one, FIA approved but out of date. I suspect its half that weight I quoted. It has the provision to take a 5/6 point at least, and thats the next task along with a roll cage. Until then I'll avoid tracks with big barriors

Post Wed May 06, 2009 3:02 pm

I've always been told that the one bonus about the hinge breaking when you're wearing harnesses is that at least in a roll the hinge might break before your neck.

I use 4 point harnesses in my car with standard comfort seats. The thing that makes me most nervous is the angle of the belts coming up from the rear.

Post Wed May 06, 2009 3:09 pm

DUBGT wrote:
I do not want to use harnesses all the time but wondered if it is possible to install them for trackdays to work safely with the OEM 'Sport' seats?

If you want to keep your sport seats, you might consider a CG Lock http://www.cg-lock.co.uk/ basically a little contraption that locks your lap belt in place so only the diaginal moves. Helps keep you located witout restricting movement and the seatbelt will work in the usual way in an accident.

Post Wed May 06, 2009 3:12 pm

Without a roll cage I would not use either.

Stonger seat with harness means you then hold the roof up, if you go upside down.

More people want the track look and think with a racing seat and harnesses they are safer when in fact all they do is placing themselves at greater risk in the unfortunate event of an incident.

Cheers

Dave

Post Wed May 06, 2009 3:12 pm

'Arr' its G force that has to multiplied by the weight. I knew it was something, its been a while since I did GSCE science.

Agreed about the seat tipping. Are harnesses approved to a certain 'weighting' then? I think I made a mistake about my seat, its a shit Corbeau Forza one, FIA approved but out of date. I suspect its half that weight I quoted. It has the provision to take a 5/6 point at least, and thats the next task along with a roll cage. Until then I'll avoid tracks with big barriors

Not that I am aware of, all that I know is that to get FIA approval it has to have an ultimate breaking strength that exceeds a certain value. I'll need to check what that value is, but its well in excess if 1000kg. I think it would be pointless to rate them according to a persons weight, since the outcome of the crash equally depends on how many g's you pulled. If you ever reach the point where your harness snaps, its probably already too late. Your internal organs can't handle that sort of deceleration and it's unlikely that you would survive.

Even if the harness does hold out, you still hear the old story of finding the driver strapped, intact, inside a brilliantly constructed moly cage, but dead from internal injuries. It's what they call "coming to a dead halt".

Post Wed May 06, 2009 3:20 pm

I agree Dave. You really need to do Bucket seat /cage /6 point harness all at the same time. If you get a good cage that has harness mounts you also remove the problem that Elecblondie is refering to.

There is no really easy way to do it, but all at once.

Post Wed May 06, 2009 3:36 pm

I agree Dave. You really need to do Bucket seat /cage /6 point harness all at the same time. If you get a good cage that has harness mounts you also remove the problem that Elecblondie is refering to.

That's exactly what I'm using on my track car - cage, harness and race-seat. All three work together in harmony. Take one away and the others become a danger to you. And not forgetting the strength of the seat mounting!

Post Wed May 06, 2009 3:48 pm

In my view when it comes to safety equipment no-one will tell you car can be too safe. Of course you need to balance all your requirements of saftey / budget / practicality etc. I used to use a CG-Lock that secured the standard lapstrap in place meaning that my lower body was not moving about during spirited driving. The benefit is that your driving is not distracted by trying to brace yourself. Obviously harnesses would be better: you could fit a harness bar that mounts behind the front seats between the upper fixing points for the seat belts. If yours is a two-door this will restrict access to the rear, although it may not be difficult to remove for 'normal' use. FIA conformation means minimum safety tolerances are met as mentioned above and full compliance would probably pass scrutineering for race events, at the expense of relative practicality (eg if you fit a full cage).

Mine is a touring with a bespoke bolt-in cage and B-pillar harness bar, buckets and harnesses. This for me is the most versatile daily driver and spirited track hack.

Post Wed May 06, 2009 5:32 pm

Mine is a touring with a bespoke bolt-in cage and B-pillar harness bar, buckets and harnesses. This for me is the most versatile daily driver and spirited track hack.

Sounds like a fantastic ride.

Post Wed May 06, 2009 5:38 pm

With all due respect Geoff, wtf is that! It certainly looks lightweight.

Any links to a build thread? Looks prime for a v8

Post Wed May 06, 2009 6:31 pm

Jon_Bmw wrote:With all due respect Geoff, wtf is that! It certainly looks lightweight.

Any links to a build thread? Looks prime for a v8

That's an E30 with the body replaced with an integral chassis-cage. I built it out of a 325i that I ripped apart, and some lengths of steel. The above pic doesn't show the body, since I wanted to hi-lite the seats attached to the frame inside the cage for the purposes of this thread. The engine is a turbocharged 2litre Toyota 3SGTE pulled back behind the front crossmember so as to improve weight distribution and reduce the moment of inertia about the vertical. The body is a combination of R5TS and R5Turbo composite panels. The floor, firewall and doors are aluminium. The only glass is the windscreen, the rest is polycarbonate, so total weight is around 750kg. She drives and handles like a mini on steroids, but shes's a well disguised E30 at heart

There are some older photos posted here, http://www.e3024v.com/board/index.php?topic=514.0, but I need to take some newer ones and introduce her to this forum some time.

Post Wed May 06, 2009 7:41 pm

Looks brilliant on the link, having a look at the link, within the 24v site as well. Cracking project.

Post Wed May 06, 2009 9:11 pm

Jon_Bmw wrote:Looks brilliant on the link, having a look at the link, within the 24v site as well. Cracking project.

Thanks Jon. I'll post a more up-to-date write-up here as well when I get a chance.

Post Wed May 06, 2009 11:54 pm

Thank you all very much for your replies on this subject. My car may become the fully fledged track car that I originally intended it to be in the future but for now it sounds like I ought to do a little research into these CG locks that you guys mentioned. If that is the safest I can be with OEM seats then it's the thing for me, for now...

Thanks again,

James.