installed BK bar and Simpson belts... too short

Shaun @ Tru6 · 05-23-2004, 04:05 PM

I installed a Brey-Krause harness guide bar and Simpson belts today.

I mounted the belts to stock seat belt locations and the shoulders are short by 6 inches for me, a good foot if you want to play with seat position, smaller drivers, etc.

Here's a pic. Did I just get belts that are too short?

jyl · jyl's Garage

Are you sure the BK bar isn't installed backwards? There seems to be an awful lot of room between the bar and the seat. That's all I can think of, besides ordering too-short belts.

Shuie · 05-23-2004, 04:48 PM

Did I miss the update on the interior? That looks awesome.

Shaun @ Tru6 · 05-23-2004, 04:51 PM

Quote:

Originally posted by jyl
Are you sure the BK bar isn't installed backwards? There seems to be an awful lot of room between the bar and the seat. That's all I can think of, besides ordering too-short belts.

Good point, and I looked at that, but the bar can only be mounted one way since it has uni-directional stays that go down to the outboard sill seat belt mounts. It really can only be mounted one way. the good part is that it ought to really stiffen the car up.

Shaun @ Tru6 · 05-23-2004, 04:56 PM

Quote:

Originally posted by Shuie
Did I miss the update on the interior? That looks awesome.

Sherman, by update I think you are referring to the 73 track car. Oh my friend, it will be some time before the interior goes in. This past week I got hte carbon front fenders, hood and left rear quarter on. Pics late tomorrow night.

I put these belts in my daily driver 84 Targa since it has the 1-piece buckets (very comfortable) and I am using it as my DE car. Last instructor strongly recommended I put proper belts in it.

ipapilot · 05-23-2004, 07:21 PM

I do think it is possible you have the wrong belts. I think they come in short and long depending on how they mount. I'm sure they can be exchanged!

75'930cab · 07:31 PM

You loop them around the bar. That's why there short. That's my guess???

ipapilot · 05-23-2004, 07:35 PM

You would only mount directly to the bar if it was the harness truss. This is only a guide bar and should not be mounted directly to... The harnesses provided would fit fine if a truss was used. Definitely cheaper just to swap out the harnesses for the correct length.

nostatic · nostatic's Garage

I believe the BK bar is offset towards the rear so you can still slide the seat back.

Zeke · 05-23-2004, 08:32 PM

There is a very comprehensive thread on this board all about seats, belts and bars. One thing I could conclude from that reading is that you might want to mount those belts higher up on the bulkhead. As a benefit, you get less of a stress angle on the harness bar. The belts should be long enough from that location. You may not want the holes in your pad, though. Commonly done with the RS style carpet. Maybe take out the pad temporarily and install the belts until your track car is ready.

Be sure to use suitable backing washers. Simpson has these.

Lindy · 05-24-2004, 07:34 AM

I have spoken with a number of both drivers and race/preperation shops who have used the B-K harness as a direct mounting point for wraparound belts for drivers ed. and autocross applications.

According to the shops (all of whom specialize in Porsche only work) that I have spoken with, the harness guide is extremely strong, the only difference being that it has not been tested to the degree that the harness-truss has been. In order to fail, the harness guide would have to break the stock mounting bolt on the driver's side, drop down to the intersection of the pillar and window sill junction and rip out the metal reinforcements in this area.

Also, I have been told that belts are not supposed to be mounted through the guide to the stock mounting points in the rear. If the harness guide did fail under extreme conditions, the driver would be subjected to a compressive (vertical) load on the spinal cord as the belts tightened between the rear mounting points and the lap belt latch.

Lindy

Shaun @ Tru6 · 05-24-2004, 08:02 AM

Thanks Lindy, good write-up. I agree about the strenght of this unit, it is a serious piece of machinery.

I think I will wrap the belts for now and have some backstays made going to the rear seat mounts making it a truss, very similar to the front stays.

nostatic · nostatic's Garage

Quote:

Originally posted by Lindy
I have spoken with a number of both drivers and race/preperation shops who have used the B-K harness as a direct mounting point for wraparound belts for drivers ed. and autocross applications.
.......

Also, I have been told that belts are not supposed to be mounted through the guide to the stock mounting points in the rear. If the harness guide did fail under extreme conditions, the driver would be subjected to a compressive (vertical) load on the spinal cord as the belts tightened between the rear mounting points and the lap belt latch.

Lindy

This isn't what I've heard, and the last part is somewhat contradictory. I know it is a no-no to mount the harness to the floor behind the seat becuase the angle is too small, but rear belt point is OK with a harness guide. Assume two possibilities:

Harness wrapped around guide bar. In an impact all of the force is directly on the guide bar.

Harness routed over the guide bar down to seat belt mount points. In an impact, only part of the force is directly on the guide bar.

Seems to me it the guide bar were to fail, it would be more likely in scenario one since the forces are greater. And in the failure, you have no retention of the upper boddy. In scenario two, if the guide bar were to fail you would still have retention, and assuming you are using a proper seat with holes for the harness, you still have some support against compression.

That being said it is likely better to mount the harness to the firewall, but my half-arsed mental calculations say rear belt/guide bar is better than direct-to-guide-bar.

Lindy · 05-24-2004, 08:34 AM

In order for a harness guide to fail (at least a B-K harness guide), the entire bar would have to break the mounting bolt, at which point it would (by design) slide down the pillar until it hit the intersection of the pillar and the rear window sill. It would then have to rip through the reinforced junction between the pillar and the sill. The was a 911 at Road America that have a major frontal impact with this bar, the driver and an instructor. The bar was one of the few things on the car (in addition to the passengers) that survived intact.

chrisp · 05-24-2004, 08:39 AM

Not sure I would mount belts direct to the bar. Wouldn't BK just market this as a mounting point if it were such? I see that someone said it just hasn't been tested for that application but why then would they design the truss (a complex part) when possibly an existing product would work? Also you are taking those mounting bolts out of single shear and introducing a bending load since the pull of the belts is not flush against the surface of the b-pillar like the stock belts do. Peak loads in a stock belt are probably lower than a 4/5/6 point set up because the stock belt is narrower webbing and the system has stretch built in. There's less stretch in your Simpson set up and therefore higher peak loads.

You've mentioned building your own truss system. You could run a piece of 3" (so it doesn't stretch under impact g-loading) webbing straight back (to slightly upwards) to the rear deck and preload it so the whole system has tension pulling it back and then, should you get in a frontal impact, that webbing would carry a significant portion of the load and keep the bar from flexing. Flexing will encourage the bolt heads to pop off.

Doesn't Simpson make a longer seatbelt? Most offer two lengths.

Wil Ferch · 05-24-2004, 08:40 AM

Nostatic is correct....don't mount directly to the bar unless it is only for low speed autocross. Talk to BK...that's why they also make "the truss" style...

Shoulder harnesses come in nominal 48" and nominal 72" lengths. You need the longer style to drape over the harness bar ( as shown and as proper).

--Wil

Zeke · 05-24-2004, 08:49 AM

This thing will never be resolved. Common sense and consenus are going to be the"guide" here. Another good data point would be SCCA Tech Rules. My copy is 2 years old now, so it's probably not current with the latest thinking. For them, a seat brace is necessary. That would solve the hinged seat issue. IIRC, the thing has to be 12 inches square. I'm sure that could be a bolt-in piece.

I don't know why, but I don't have any problem with lateral support and body stability with my stock early sport seats. I could use a touch of additional lumbar support. As such, I'm reluctant to change them out for now.

chrisp · 05-24-2004, 08:58 AM

from the 2004 PCA racing rules

Safety Rule 25: A seat back brace is not required in cars equipped with an FIA-approved seats and FIA approved factory seat rails. The seat must be replaced after 5 years from the date of manufacture.

Shaun @ Tru6 · 05-24-2004, 10:31 AM

Great discussion. I can get longer belts, Simpson is great to work with. But I think I am going to go another route:

The bar ends have angle plates used for attachment to the B pillar. This provides a nice -25 degree (pointing to the rear sheet metal) angle flat surface. Given that, using the same tubing as the bar with a small flat plate welded to one end which will bolt to the bar and the othendwtih a plate that will bolt to the rear sheet metal, but be able to sneak under the rear pad at the very edge.

Either that or for no money or hassle get longer belts.

chrisp · 05-24-2004, 10:43 AM

Your idea would be pretty stout as long as the rear deck can handle that type of pulling loads.

Even though I come up with some pretty creative stuff and own my car so I can have fun doing cool things, I would not put safety parts design in my own hands. Sure, if I am just duplicating an existing design (like having my own roll bar made) it's okay but there's no way to test your own designs without potentially paying the ultimate price.

I would get longer belts.