Modifying Harness Holes In Seat

[AMR33]

Hey folks, got a curly one. I bought a sparco pro 2000 seat and installed it in the r33. the seat is equipped to run a 6 point harness which is great. One issue I am having is that my shoulders sit a bit above the bottom of the top holes for the harness. As you may/not know, your shoulders should sit below the holes so that the harness rests on the bottom of the hole rather than the shoulders (if you know what I mean).

Now I was thinking of making up some "spacers" and drilling them into the existing holes; effectively making the holes sit above my shoulders.

For those few who understand what I'm on about, what are your thoughts on this course of action?

Cheers

Amir

[james32gtr]

2 options

1: shrink

2: add something to the bottom of the holes to make harness sit higher (may not be a great idea drilling the seats, try and find some plastic sleeve you could perhaps slide over the holes to make them higher)

[AMR33]

Option 2 is what I was thinking. But I think it might be a silly idea and if they come loose in a crash or something then I may have a problem. Best bet to get a seat that fits I guess. But that means going XL seat which means it will be much wider (Im quite slim) and will defeat the purpose. Its really hard finding the right size seat

[warps]

One issue I am having is that my shoulders sit a bit above the bottom of the top holes for the harness. As you may/not know, your shoulders should sit below the holes so that the harness rests on the bottom of the hole rather than the shoulders (if you know what I mean).

Sorry for the late reply - only just saw this.

Don't know where you got this misinformation but it is WRONG. There is absolutely nothing wrong with the strap running across your shoulder and not touching the seat, in fact this is better for the harness. There are exceptions to this rule, but only if the harness is located low, in which case the seat becomes a structural part of the harness load path (which requires seats specifically made for this purpose).

Here's one good guide for harness installation. I'm sure there are plenty of others out there.

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

Don't start modifying your seat. Just think: will the mods you make be capable of withstanding a 20G deceleration with your body weight?

[AMR33]

I've seen and gone through that guide before, cheers man. It didnt mention that the shoulder belts should not run straight accross the shoulder. The idea is that if the shoulder belt is resting on the driver's shoulder, in a crash it will push down on the shoulders and could compress the driver's spine. This is why it should run accross the seat and then down towards the shoulders pulling the driver back into the seat (as opposed to pushing down on the driver).

Why do you say its better for the strap to rest on the driver's shoulders?

Cheers for the input

[warps]

As I said earlier, if the harness is mounted to the floor, and the angle of the harness to horizontal is greater than 20 deg (as per the Schroth guide) then this will put excessive vertical load onto you, or the seat. In that case, if you have the correct seats (designed to withstand that type of force) you can get away with the harness angle closer to vertical. This is the least optimal way to do it - best to have the harnesses coming into the seat as horizontal as possible

If you have the harness correctly mounted, ie less than 20 deg, then you don't need any special seats, and the harness is supposed to go over your shoulder. The small vertical component of the load won't be enough to cause any damage to your spine.

Also, having the harness rest on your shoulders means it's not rubbing on the edge of the hole (I've seen some seats with pretty rough edges on these holes). This protects the harness from abrasion.

In the first scenario above, if there is a slight gap between the harness and bottom of the hole, this won't cause any problem as your shoulders will easily conform a bit (half a hole height) under the load of the harness, and won't put any excess load onto your spine.

If you're really concerned about it, call the harness and / or seat suppliers and talk to them. Send photos if you need to. If your harnesses are mounted to the floor, and you haven't got the right seats, then you'll be in a world of hurt, regardless of whether the harness goes over your shoulder or the edge of the hole in the seat.

I can see where you got your idea from, but am concerned that you have misinterpreted the reasoning behind it.

[AMR33]

I see. If I run the harness I am planning to use a harness bar and have the shoulder belts as horizontal as possible.

[warps]

No problems, In that case it sounds like your seats are fine to use as they are. As long as passing through the hole in the seat keeps the harness in a fairly straight line, all should be sweet.

Just pay attention to the rest of the harness installation instructions - I've seen a lot of dodgy installs.

Also don't buy second hand harnesses (in case you're wondering). You never know the life a second hand harness has had. Good quality new harnesses aren't that dear.

[AMR33]

Yeah your right. New 6 point harnesses are within the $300 range so its worth buying brand new. The seat I have is Sparco Pro 2000 which is FIA approved for another 2-3 years.

[warps]

I'm not 100% certain on this, but I believe that seats don't "expire" like harnesses do. Maybe at international level events (or possibly even national) they might, but apart from that they have no use by date..

Oh, and harnesses currently have an additional 5 years after the use-by date on the label.

[AMR33]

Cheers for the advice