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mulik52
I find it interesting how a lot of points discussed and argued here are explicitly shown in this mounting instructions: https://www.schrothracing.com/sdocs/2009_Competition_Instructions.pdf

The pics on page 11 show clearly that belts stretch a lot (therefore you want shortest possible belts as even in that configuration there will be a lot of give. And you certainly want your belts to stretch, irregarding the timing of peak deceleration, as having bells stretch will necesseraly reduce the total energy which needs to be absorbed by the body. But if they stretch too far then you hit the steering wheel defeating the point of the belts). The pics also show why one might want to wear Hans device, look at the motion of the head without hans. Finally, they explicitly state that shoulder harness should not be mounted below shoulder levels, or spinal column compression will result. As someone pointed out, Hans will exacerbate this requirement, potentially explain all those spinal column compressions.

Klim

Tavarich Klimsli, the page 11 shows "scary pictures' and that is the intent and that is all it shows. No Data at all therefore NOTHING can be concluded..
I think you have just show the "fallacy of "logic'.

In other words it shows something "true" ie "belt stretch" but no data to make that information useful.

We have no idea of weigh of the dummy, rate of deceleration, type of "barrier" length of belt, material of belt, nothing really but scary photos.. And your conclusion should be tempered to something like "below shoulder...MAY result in" since reality has shown us over the years that many people have crashed with harnesses below shoulder without spinal injury. (I was always told it would injure shoulders)..

Belt stretch should be expressed in % of stretch per length ie 2%/foot or something like that.

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Comrade John, please refer to Page 9 of the same brochure:
90 degree head on collision
75 kg dummy
50kph
Stopping distance of 400mm
Peak of 30g


klim

Quote
john vanlandingham
Belt stretch should be expressed in % of stretch per length ie 2%/foot or something like that.

So, using the hypothetical number above, a 2 foot belt would stretch 4% and a 14 foot belt would stretch 8%? Wouldn't 2% be 2% regarless of the belt length?

---

First Rally: 2001
Driver (7), Co-Driver (44)
Drivers (16)
Clerk (10), Official (7), Volunteer (4)
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Last Updated, January 4, 2015

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john vanlandingham
Blame is for idiots. losers.

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Morison

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john vanlandingham
Belt stretch should be expressed in % of stretch per length ie 2%/foot or something like that.

So, using the hypothetical number above, a 2 foot belt would stretch 4% and a 14 foot belt would stretch 8%? Wouldn't 2% be 2% regarless of the belt length?

Wow, you're good with math.
That's how % works. 2% is 2%....

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Easy guys, I best nip this in the bud, the full moon was last week, get a grip of your hormones and menstrual cycles please, potentially they are running seven days retarded. T'internet is already full of shit this week. There's no more room available for pedantically splitting hairs please.

---

Disappointingly not yet a Jackass

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john vanlandingham

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Morison

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john vanlandingham
Belt stretch should be expressed in % of stretch per length ie 2%/foot or something like that.

So, using the hypothetical number above, a 2 foot belt would stretch 4% and a 14 foot belt would stretch 8%? Wouldn't 2% be 2% regarless of the belt length?

Wow, you're good with math.
That's how % works. 2% is 2%....

Shelve the attitude John - I was asking a question so I could get some clarification on what you were saying. Which is why I asked the question.

Your initial comment was that the stretch should be indicated in % of stretch per length... The only reason to have 'per length' would be if the percentage of stretch increased with the length of the belt - otherwise straight percentage of stretch is all that is needed.

2% stretch of a 4 foot belt means it becomes. 4.08' long, or it gains .96 inches.
4 x 1.02 = 4.08

2%/foot of a 4 foot belt means it becomes 4.32' long, gaining. 3.84"
4 x (1+(4*.02)) = 4 x 1.08 = 4.32

The suggestion seemed to be that the percentage of stretch changes with the length of the belt, which I found odd.

---

First Rally: 2001
Driver (7), Co-Driver (44)
Drivers (16)
Clerk (10), Official (7), Volunteer (4)
Cars Built (1), Engines Built (0) Cages Built (0)
Last Updated, January 4, 2015

Quote
john vanlandingham
Blame is for idiots. losers.

Fucks sake, don't over analyse this or the rule makers will notice this discussion on the web. You really don't want the FIA thinking to deeply about this or the can of worms will be well and truly opened.

I mean, even with my current drunken grasp of physics, mass, momentum etc surely "belt stretch" is going to be a variable based on the velocity of impact and the body mass of the crashing occupants of the car, not a constant.
This being the case only thin lightweight people will be allowed to drive fast using propriety and currently acceptable belt standards, and fat dudes will either have to drive slower or pay for a more expensive belt to cope and give an acceptable level of restraint when compared to the thin guys in a similar accident.
I think that is fair, or maybe the specifications regarding the proximity of roll cage, steering wheel, etc, to the occupants could be a variable dimension based on their bodyweight to compensate for "belt stretch"......

---

Disappointingly not yet a Jackass

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danster
"belt stretch" is going to be a variable based on the velocity of impact and the body mass of the crashing occupants of the car

Mass, definitely. But not velocity.

A relatively slow impact into a fixed barrier might be much more dangerous than a high speed impact through a haystack.

Sudden and large change in velocity is what's dangerous, i.e. acceleration/deceleration.

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Ferdinand

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danster
"belt stretch" is going to be a variable based on the velocity of impact and the body mass of the crashing occupants of the car

Mass, definitely. But not velocity.

A relatively slow impact into a fixed barrier might be much more dangerous than a high speed impact through a haystack.

Sudden and large change in velocity is what's dangerous, i.e. acceleration/deceleration.

Now I have already admitted to being DUI (drunk in charge of a keyboard whilst under the influence), and have also managed to pack in another fine glass of wine since I last posted, so my grasp on reality is a variable and most likely slipping. But surely Newton's 2nd law of physics comes in to play here?

---

Disappointingly not yet a Jackass

Quote
danster
surely Newton's 2nd law of physics comes in to play here?

Correct.

F=ma

The Force applied to the belts is proportional to mass times acceleration.

Speed (velocity) is not what kills. It's change in speed (acceleration), particularly if it's a large and sudden change.

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Ferdinand
It's change in speed (acceleration), particularly if it's a large and sudden change.

And that's why we have restrictors! They limit acceleration right?

Okay, so 2% stretch, that means we're all fucked in a very short time period.
2 ft*1.02 = 2.04. It's only a matter of time until it's 3 feet and you're dead. That reminds me of a band called Anal Cunt. As I recall, every song was like 5 seconds long and ended with the lyric "you're dead."

---

Grant Hughes

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Morison

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john vanlandingham

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Morison

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john vanlandingham
Belt stretch should be expressed in % of stretch per length ie 2%/foot or something like that.

So, using the hypothetical number above, a 2 foot belt would stretch 4% and a 14 foot belt would stretch 8%? Wouldn't 2% be 2% regarless of the belt length?

Wow, you're good with math.
That's how % works. 2% is 2%....

Shelve the attitude John - I was asking a question so I could get some clarification on what you were saying. Which is why I asked the question.

Your initial comment was that the stretch should be indicated in % of stretch per length... The only reason to have 'per length' would be if the percentage of stretch increased with the length of the belt - otherwise straight percentage of stretch is all that is needed.

2% stretch of a 4 foot belt means it becomes. 4.08' long, or it gains .96 inches.
4 x 1.02 = 4.08

2%/foot of a 4 foot belt means it becomes 4.32' long, gaining. 3.84"
4 x (1+(4*.02)) = 4 x 1.08 = 4.32 OR a little over 8,12mm longer--if the 2% figure plucked out of the air as an example..

The suggestion seemed to be that the percentage of stretch changes with the length of the belt, which I found odd.

Only to you...

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Quote
john vanlandingham
The suggestion seemed to be that the percentage of stretch changes with the length of the belt, which I found odd.

Only to you... [/quote]

So help me then.
You said "Belt stretch should be expressed in % of stretch per length"
Why does 'per length' come into it at all?

Or did you misspeak when you said that. (and it really is OK if you did)

---

First Rally: 2001
Driver (7), Co-Driver (44)
Drivers (16)
Clerk (10), Official (7), Volunteer (4)
Cars Built (1), Engines Built (0) Cages Built (0)
Last Updated, January 4, 2015

Quote
john vanlandingham
Blame is for idiots. losers.

Keith -

He's claiming that it's non-linear, which could easily be true. There's no freaking way that it's anything like X%/foot, but it's almost definitely not a simple percent, either.

edit: I find John's participation in a discussion of belt-stretch to be amusingly appropriate in the extreme, given that it isn't acceleration that matters, but the next derivative above, which is known as "jerk"



Edited 1 time(s). Last edit at 09/26/2013 08:04PM by Iowa999.

Quote
Iowa999
He's claiming that it's non-linear, which could easily be true.

Agreed, but the non-linearity shouldn't be in the length of the sample should it?
Clearly more stretch with more force applied and I could see stretch under a jerk load being different than the same load applied over time. (I've seen enough tow straps break)

Also, he did quip back that 2% was 2% ...

---

First Rally: 2001
Driver (7), Co-Driver (44)
Drivers (16)
Clerk (10), Official (7), Volunteer (4)
Cars Built (1), Engines Built (0) Cages Built (0)
Last Updated, January 4, 2015

Quote
john vanlandingham
Blame is for idiots. losers.