8 replies to this topic

[Randy Wolfgram]

Okay, time for my first (of what will likely be many) newbie question :-)  Can the lap belt anchors also be used for the sub belts on a 6 point harness?  As I mentioned in my intro thread, I just picked up a "mostly" race ready SM, but I need belts and there is nothing to anchor a sub belt to under the seat.  In our Lemons car, we have an eye bolt under the seat to attach the sub belts to, so was expecting something similar here, but not sure what's allowed.  Do I need to get an anchor installed under the seat or can the lap belt anchor points be used?

 

Thanks in advance

[Ron Alan]

Not sure...but it would seem to defeat the purpose of the lap belt and what it's function is. I referenced this when trying to answer the same question ...

http://www.schroth.c...s/en/index.html

With most Miata seats on the floor, the perfect location for the sub belt is hard to achieve.

[RussMcB]

What kind of seat?

 

You can anchor the sub belt of a 6 pt harness at the same locations as the lap belt.  However, 6 pt belts are for "lay down" cars (formula cars), not cars like ours with a more upright seating position.  In our cars the sub belt is mainly for keeping the lap belt in the right position, and a 5 pt harness will be better.

 

[Mitch Reading]

What kind of seat?

 

You can anchor the sub belt of a 6 pt harness at the same locations as the lap belt.  However, 6 pt belts are for "lay down" cars (formula cars), not cars like ours with a more upright seating position.  In our cars the sub belt is mainly for keeping the lap belt in the right position, and a 5 pt harness will be better.

 Not sure I agree with you on 6pt vs 5pt belts, but I'm not an expert.  Make sure you speak to someone who is before taking wisdom from us knuckleheads.

[Randy Wolfgram]

Thanks guys.  

 

Russ, where are you mounting your sub on the 5 point harness?

[ChrisA]

What kind of seat?

 

You can anchor the sub belt of a 6 pt harness at the same locations as the lap belt.  However, 6 pt belts are for "lay down" cars (formula cars), not cars like ours with a more upright seating position.  In our cars the sub belt is mainly for keeping the lap belt in the right position, and a 5 pt harness will be better.

No, a 6 or 7-point is preferred, 5-point is considered minimal according to the GCR.

Randy read the Schroth belt mounting instructions they are very thorough. A PDF version can be found here: http://www.hmsmotors...-installation  

Note that the anti-sub belts need to be able to withstand a lot of force, as much of the load placed on the shoulder harnesses in head-on collision is directed through those. So make sure your mount point is correct and strong.

 

An exerpt from the Schroth instructions:

WHAT HAPPENS DURING A FRONTAL IMPACT:

This data is based on an optimised installation with an upright seating position during dynamic testing. It simulates a 90° head on collision, utilising a 75 kg [165 lb] mass dummy, an impact velocity of 50 kph [31 mph] and a stopping distance of approximately 400 mm [16”] with a maximum deceleration of 30 g [FIA 8854/98 dynamic test requirements]:

The pelvic load, expected to surpass 14 kN [3,100 lb] at each side, will elongate the lap belt and compress the tissue on the pelvis. The pelvis will slide forward by 80 to 100 mm [3”-4”]

The upper torso load is expected to surpass 7 kN [1,550 lb] on each strap, will elongate the shoulder belts, the upper body will roll in, the adjusters will move up the chest by approximately 200 mm [8”] and forward head trajectory will be up to 400 mm [16”]

The pelvic movement combined with the shoulder belt forces will load the anti-sub straps to more than 6kN [1,320 lb] each in a 5- or 6-point racing harness and can be intentionally higher in a F-type model where the anti-sub straps are routed rearwards.

In more reclined seating positions, the pelvic load will be reduced to approx. 9 kN [2,000 lb] since the seat pan, designed as a ramp, will take some of the load. Therefore it is essential the seat or chassis manufacturer ensure the seat pan is strong enough not to bend or even collapse under extreme loads.

In any case, seats are a significant component of the safety system! 

[Randy Wolfgram]

 Not sure I agree with you on 6pt vs 5pt belts, but I'm not an expert.  Make sure you speak to someone who is before taking wisdom from us knuckleheads.

 

Ya, this seems to be one of those topics.  I did some additional poking around and there seems to be lots of debate on the 5pt vs 6pt.  I looked at the GCR before posting here and it looks like anchoring to the lap belts is an approved method, but I'm more than willing to concede that I could be interpreting what I read incorrectly, which is why I reached out here.  My two main concerns are what is permitted by the rules of the sanctioning body and what is the most appropriate for our cars specifically from a safety standpoint.  I haven't looked in a lot of cars (naively, it didn't really occur to me to check which harness people are using), but now I'm just wondering what flavor (5pt or 6pt) most are using in their cars...

[Randy Wolfgram]

 

No, a 6 or 7-point is preferred, 5-point is considered minimal according to the GCR.

Randy read the Schroth belt mounting instructions they are very thorough. A PDF version can be found here: http://www.hmsmotors...-installation  

Note that the anti-sub belts need to be able to withstand a lot of force, as much of the load placed on the shoulder harnesses in head-on collision is directed through those. So make sure your mount point is correct and strong.

 

An exerpt from the Schroth instructions:

WHAT HAPPENS DURING A FRONTAL IMPACT:

This data is based on an optimised installation with an upright seating position during dynamic testing. It simulates a 90° head on collision, utilising a 75 kg [165 lb] mass dummy, an impact velocity of 50 kph [31 mph] and a stopping distance of approximately 400 mm [16”] with a maximum deceleration of 30 g [FIA 8854/98 dynamic test requirements]:

The pelvic load, expected to surpass 14 kN [3,100 lb] at each side, will elongate the lap belt and compress the tissue on the pelvis. The pelvis will slide forward by 80 to 100 mm [3”-4”]

The upper torso load is expected to surpass 7 kN [1,550 lb] on each strap, will elongate the shoulder belts, the upper body will roll in, the adjusters will move up the chest by approximately 200 mm [8”] and forward head trajectory will be up to 400 mm [16”]

The pelvic movement combined with the shoulder belt forces will load the anti-sub straps to more than 6kN [1,320 lb] each in a 5- or 6-point racing harness and can be intentionally higher in a F-type model where the anti-sub straps are routed rearwards.

In more reclined seating positions, the pelvic load will be reduced to approx. 9 kN [2,000 lb] since the seat pan, designed as a ramp, will take some of the load. Therefore it is essential the seat or chassis manufacturer ensure the seat pan is strong enough not to bend or even collapse under extreme loads.

In any case, seats are a significant component of the safety system! 

 

 

Thanks, Chris!

[Alberto]

Use the Schroth install instructions to identify rough location for the sub belt attachments in the floor. 

 

You'll wind up drilling 2 holes for the 6 point harness - one on each side of the frame rail.  You'll want to start with a small pilot hole to ensure you aren't drilling in the middle of the frame rail.

 

The most recent SCCA GCR will provide rules on what the proper reinforcements for the belt attachment points at the floorboard.  Get the most recent version under "Updated Rule Book".  I believe you'll need something like this:

http://www.saferacer...g-back-up-plate

I think that's what I used.  You'll also need an eyebolt like this:

http://www.saferacer...e-eye-bolt-50mm

 

 

The 6 point harness is way better than the 5 point.  No contest.  Far more comfortable on the family jewels.

 

SafeRacer is a forum vendor/advertiser iirc.  If you wind up ordering from them, Google for the Spec Miata discount code.  I think they give us 10% off or something like that.