Sam's build thread

[Sydneykid]

I've had 30 plus track day, hillclimb, race cars that I have worked on and not one had a problem with the rear seat belt angle using the lower seat belt mounting points. Some of them were much smaller than a Polo, so I'd be very surprised if it's any different.

The reason for the angle limitation is to avoid vertebra compression. They don't want the seat belt compressing your spine when you get thrown forward in an accident. Before that reg we used to see cars with the seat belt shoulder straps mounted straight down to the floor directly behind the seat. That's where the minimum 45 degrees comes from. I've never actually seen anyone measure it, we just look and if it's at a "reasonable" angle then we move on.

If your shoulders are higher than the seat back (or level with it) where the shoulder straps go, then the seat itself should be fine.

OEM seats/recliners are OK in forward accidents (the seat belt does its job), but in any decent rearwards or angular accident they break surprisingly easily. My son went LHS rear into the wall at Eastern Creek turn 1 (around 160 kph) and the hit destroyed the OEM Recaro in the Evo.

Cheers
Gary

[sambb]

stoked.... I measured the angles properly off the seat down to the rear seat belt anchor points. Measuring from the angle of my spine its only a 30 degree divergence from the ideal 90 degrees down to those points ie well within the 45 degree rules.
So I can just bung eye bolts into those points and also the front bolt of the slider rail. I'm not sure if there's room to put one in on the seats buckle mounting point against the centre console. With kids getting in and out and the seat sliding fwd/back on its rails it might tear up the carpet, so it may be that I need to drill into the tunnel furtherback. But either way it looks like a 4 point is just a plug and play and a 6 point looks east enough too once I can find someone to upholster the seat once I hack a slit into it for a crotch strap.

I've seen pull through bezels sold - ones where you can reinforce/dress holes cut in your seat back for harness shoulder straps. Anyone seen something similar to these sold so that you can line a hole cut in a seat base for a crotch strap?

[sambb]

Ok Ive had a really good look at the base of the factory seat in the Polo and I'm pretty well resigned to the fact that the seat cant be modified for a 5/6point harness. It took forever to get the seat base cuddy removed (64 screws and clips holding it in in typical teutonic fashion) so that I could get a good look underneath. With the seat unbolted it was clear that there is far too much steel plating under the seat cushion to be able to get a 5/6 point crotch strap through. There is a bit of a void but the problem is there is a nest of bars and adjusters etc under there that run pretty flush to the floor that would prevent a crotch strap getting cleanly through even if you could enlarge the hole in the steel base which I don't think you could without a grinder that would burn everything.

There are two plugs under there. One is a two wire which is for recognition that a seat belt is plugged in. I might bridge that so I dont get the annoying seat belt alarm. The other 3 wire plug is for the airbag. It would need to have been resistered out if a new seat was to be fitted. But I have neither the $ for a nice 1 piece.

So I've made the decision. After watching/hearing a felloe hillclimber nearly kill himself last year I'm not going to hold off anymore. Better to get something in even if its not the whole seat/harness etc caboodle. I'm going to go for a 4 pointer. Not a run of the mill one but one of the proper ones with anti submarine strapping on the inside shoulder to combat the normal 4 point harnesses biggest vice - the fact that in a head on you can submarine/slide underneath the waist strap. That's why 6 pointers are the go for racing. The crotch strap acts to prevent submarining and allows you to get the ideal shoulder strap tension without the shoulder straps lifting the waist strap which can cause submarining with 4 pointers.
So from what I can find, a 4 point harness will be safer than a lap sash provided the waist strap fixing points are in the ideal positions AND the inside shoulder strap has anti submarining tech built into it. ASM basically allows your inside shoulder to move a squidge more before it is arrested than the door side shoulder. This twist in the torso causes the waist belt to dig into the waist (same deal as a lap sash) to prevent you sliding under it. So its safer than a lap sash because it wont let you submarine yet holds you much closer to the seat during the crash - the lap sash lets you move miles before it arrests you, and in other collision angles is apparently much safer than a lap sash.
The only two brands I could find that have ASM 4 pointers are Takata and Scroth. This is the one i'll probably get because it has a proper latch mech (the takata has a normal seat belt kind of latch) and it has a 2 inch waist belt (apparently digs in more than a 3 inch to prevent submarining). Both have 3 in shoulder belts as I wont be using a HANS:

Schroth Clubman II-ASM-4 Black | HARNESSES | Revolution Racegear


All I need are 2 x eye hooks M10 fine for the rear seat belt positions, another for the side of the centre console tunnel and another to screw in on the front bolt hole of the seat belt slider rail. So 3 of the 4 bolts are plug and play and only the inside waist belt one will need to be drilled. An alternative to that is screwing a spec strap on underneath the existing seat belt latch mech that the harness can clip on to but I'm not sure I'll get the right angles on the waist belt if I use that.

anyway. that's the plan. I'd have loved to use a 6 pointer but I only have enough money for a seat OR a harness not both, and as the seat cant be modded for a 6 pointer, then a 4 pointer will have to get me through this year until I get afford some more safety down the track.

[metalhead]

Sounds good to me.

I've had some dramas over the weekend with the car. I might be pushing it to make Bathurst now, though you can bet I'll do all I can.

[simon k]

good plan, take pictures so I have something to copy... I love the Polo seat, but would like to be held more securely

I wouldn't be concerned about the Takata latch, just the looks and comments you'd get about airbags... How long are the shoulder straps on that Schroth? will it need extensions?

I already have the 4x M10 eye bolts, they were rattling around on the floor of that Honda I worked on and happened to land on my bench.

[sambb]

Yeah I like the seat too. The side bolsters are unreal. I was assumed because its OE that its inherently crap until I went in a few other cars and couldn't believe how rubbish they are or made for someone who must be 150kg in size. The whole unit weighs like 24kg though which does make an 8kg 1 piece look very attractive.

Have you test fit those bolts. To my eye they are metric fine.. Hopefully yours are cos I was a bit concerned that they might be something that are hard to find.

And yep i'll head down to the race supplies shop today to find out if those straps are long enough. Hope so because that harness has everything I need. Even if it only just reaches the rear seatbelt points that wouldn't be good enough as eventually I do want it coming off a proper harness bar a bit further back and higher at the 'strut' towers. Otherwise it will be this Takata:

Race Harness Takata Drift III 4pt ASM Harness. 3" Shoulder, 2" Lap

edit: race shop had all the bits with M10 fine 8.8 grade in plentiful supply. $50 bucks. No Scroth 4 pointer in stock so waiting on the supplier to give shoulder strap measurements.

[sambb]

Sounds good to me.

I've had some dramas over the weekend with the car. I might be pushing it to make Bathurst now, though you can bet I'll do all I can.

No - what happened mate? We have exactly one month so hopefully you'll make it.

[sambb]

[simon k]

looks alright - hopefully you'll never find out if they work

[sambb]

Ok so the middle back seat anchors is the long bolt and the short ones come from the sliding rail by the door and the rear drivers side. I bought eye bolts that matched those lengths maybe a tad longer. The rear drivers side eye bolt can stay there as its well out of the way. Same goes for the middle rear. The seat base clicks into place aok with them fitted. I race with my seats out though and the middle belt has to be undone anyway to achieve that so I'll just screw that eyebolt in at that time. At the angle the shoulder straps will fall off the back of the seat, although it looks tight and provided you orient the eye bolts correctly, the clip on's wont foul on anything.
The slider rail thing is dead easy too. Its possible I could have just clipped onto the rail with the harness but I think the latch would have fouled on the trim and not sat right and given you a false sense of seat belt tightness and would have been capable of a bit of twist in an impact and loosing a bit of waist tension in the process. The eye bolt will position the harness clip out of the way and further back to give a really good position for the belt. I only had to knick a little sliver off the edge of the carpet to get it sitting flush around the bolt. Last thing tonight is to drill and mount the other waist belt eye bolt into the side of the centre console/exhaust tunnel directly across from the other one. Unfortunately the OE latch mech which is attached to the seat itself is on a rigid strap that is bent at all kinds of angle to clear the adjuster mechanism and putting another strap onto that bolt point wouldn't have worked. However on the passenger side there is enough clearance to do the same.
Last thing I did was meter the seat belt electrics. I measured incorrectly the other day and gave a bum steer I think regarding its resistance. I think I accidentally measured up towards the ECU. Its pretty simple really. Closed circuit for if the belt isn't latched and open circuit if it is plugged in/latched. So it couldn't be more simple - you just unplug the red plug making it O/C and the car thinks you are wearing the belt = can wear a harness without the OE belt and wont be subjected to the seat belt alarm and in case the car needs to see the belt plugged in to fettle airbag deployment pressures (some cars do this but no idea if ours does) then that is taken care of at the same time too.