Harness Mounting - Shoulder belts
11-26-2007, 10:13 PM
#16
Burning Brakes
You know, something else I see a lot and disagree with, is when the shoulder belts angle downward as they go back. Seems to me they should go straight back. When they are angled downward, as you press forward, they would seem to have a spine-compressing effect. I'm sure this has been covered also but I'm interested in John's take on it.
11-26-2007, 10:31 PM
#17
Drifting
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So how come the engineers at Porsche and various other professional racecar builders and teams continue to mount the belts this way if it is less safe than other options? They could easily weld a bar to the main hoop that doesn't reduce the amount of seat adjustability and weighs the same as the current bar.
11-26-2007, 11:05 PM
#18
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Still, same result. No matter what it is relative to, the body is still moving when the Earth isn't (in this regard) and the car isn't as much (after it hits something), and the time that the body continues to move is critical. Stop it quick, and in as linear a fashion as possible, reducing the whip, and the overall load.
Now that's not to say don't want to control the body quickly. The harness should still be tight in a static state, not loose. The quicker you control the body, the better. The quicker you stop the body, the worse.
11-27-2007, 12:18 AM
#19
Three Wheelin'
If any of you ever want the right answers on these topics, contact Joe Marko at HMS Motorsports in Peabody, MA.
I have bought some things from him and consulted with him in the past. He is mentioned in the latest Pano. I encourage you to become informed from professionals with racing pedigrees.
By the way, I'd bet that the fellow in the accident at Sears was going nowhere near 80 when he hit the truck.
- Mike
Porsche Racing Club
I have bought some things from him and consulted with him in the past. He is mentioned in the latest Pano. I encourage you to become informed from professionals with racing pedigrees.
By the way, I'd bet that the fellow in the accident at Sears was going nowhere near 80 when he hit the truck.
- Mike
Porsche Racing Club
11-27-2007, 01:55 AM
#20
So how come the engineers at Porsche and various other professional racecar builders and teams continue to mount the belts this way if it is less safe than other options? They could easily weld a bar to the main hoop that doesn't reduce the amount of seat adjustability and weighs the same as the current bar.
11-27-2007, 03:09 AM
#21
Burning Brakes
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OK Gregg;
Point taken. I'd forgotten that. Simon is likely right. It would take someone way smarter than me to work it all out, and I'm sure it has been.
Still, same result. No matter what it is relative to, the body is still moving when the Earth isn't (in this regard) and the car isn't as much (after it hits something), and the time that the body continues to move is critical. Stop it quick, and in as linear a fashion as possible, reducing the whip, and the overall load.
The thing that makes this all work is that when they started crash testing in earnest, they found that it was the violent stop at the end of the long stretch that killed you, not the stop alone. Just like jumping off the building. It's the sudden stop after the long fall. Jump 6" and it doesn't hurt as much.
The human body can take WAY more stress than anyone realized (except the neck) if the term is short. Stop it quick then made sense!
Point taken. I'd forgotten that. Simon is likely right. It would take someone way smarter than me to work it all out, and I'm sure it has been.
Still, same result. No matter what it is relative to, the body is still moving when the Earth isn't (in this regard) and the car isn't as much (after it hits something), and the time that the body continues to move is critical. Stop it quick, and in as linear a fashion as possible, reducing the whip, and the overall load.
The thing that makes this all work is that when they started crash testing in earnest, they found that it was the violent stop at the end of the long stretch that killed you, not the stop alone. Just like jumping off the building. It's the sudden stop after the long fall. Jump 6" and it doesn't hurt as much.
The human body can take WAY more stress than anyone realized (except the neck) if the term is short. Stop it quick then made sense!
I'm with John - I'm sure you don't want the driver to be moving much with respect to the vehicle. John's description of the "whip" is a good one.
With respect to the "long" belts in the OP, I think it *might* be to minimise the angle change for taller vs shorter drivers. Perhaps the factories have analysed that the risk of a steep shoulder harness is greater than a shallow angle on a longer belt. Personally I've side-stepped this issue by having a higher harness bar welded in to my rollbar, and lowering my seat to get both a short run and a shallow angle.
11-27-2007, 09:12 AM
#22
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The physics of what John sasy is sound as I understand it. MY guess at the reason for the disparity in what you see is because John builds cars for you and me custom. They build cars for anyone between 5' and 7' tall. The geometry is simple. The farther back you mount the belts the greater number of driver sizes you can accomodate and still be in the acceptable range of belt angles w and w/o HANS. If you make the belt attachment point right behind the seat for my 5'4" body it is totally wrong for my 6 ' buddy sharing my car in an enduro. Building a car is always a compromise and it is always less of one if I build everything just for me.
11-27-2007, 09:28 AM
#23
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That is an absolutely stand-out observation. Kudos, Sir. Wish I'd tought of it myself! As FBB said, they are building for everyone they can get to drop the coin to own one. Stuck is 6-2-ish, and Long is... well... not. Everyone is free to customize from there to suit their needs. That's why I put NOTHING on my roll bars.
A slight angle downward from shoulder to terminus give a slight bit of compression, and this aids body as well as HANS retention. When you cinch down, you can feel the difference of only a few degrees.
I also encourage people to seek out expert opinion. Get as many as you can. Please do call HMS Motorsport so they can corroborate what I've said. Nobody knows/remembers everything or gets everything right every time they say something, but we've gotten whatever knowledge we possess from a lot of the same sources!
11-27-2007, 11:08 AM
#24
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It definitely does cause a compression effect but I believe it is 'safe' with up to something like 15 degrees of ange downwards. I know Simpson recommends mounting between 0-15 degrees for harnesses and they make those things for racers that crash at over 250mph like top alcohol dragsters.
11-27-2007, 04:11 PM
#25
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Thanks for the conversation. This is a good topic. I spent a lot of time worrying about my install and I spent a lot of time with the Schroth manual
https://rennlist.com/forums/997-gt2-gt3-forum/383245-harness-mount-question.html
http://www.schroth.com/installation-.../en/index.html
https://rennlist.com/forums/997-gt2-gt3-forum/383245-harness-mount-question.html
http://www.schroth.com/installation-.../en/index.html
11-27-2007, 07:17 PM
#26
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11-28-2007, 09:27 AM
#27
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No, no, no; I'm 100% with ya. Excellent summary. You nailed it.
11-28-2007, 10:46 AM
#28
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One thing you want to avoid in your configuration I believe is if you have a downward angle on the harness, you want to ensure that after "your" compression the harnesses have not dropped low enough such that the seat becomes a pivot / support point. This could cause all sorts of problems if the seat breaks during impact as it wasn't designed for the forces being applied.
cheers,
Jeff
cheers,
Jeff
11-28-2007, 10:55 AM
#29
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From the Schroth manual itself!
"Extremely long shoulder belts allow for extra elongation and head movement and must be avoided."
"Long shoulder belts also provide more slack in the rebound phase so the belts may slip off the occupant's shoulders"
However define long and extremely
"Extremely long shoulder belts allow for extra elongation and head movement and must be avoided."
"Long shoulder belts also provide more slack in the rebound phase so the belts may slip off the occupant's shoulders"
However define long and extremely
11-28-2007, 01:51 PM
#30
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I've fallen afoul of too many Gs, and didn't see it until the above. I meant Greg Smith. It sounds the same, you know? Greg... Gregg... Or is the latter GregGUH? It's all so much work!
I understand what Simon was saying, I believe. While it may be splitting hairs, it is likely accurate.