Ivan
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| posted on 30/10/08 at 11:38 AM |
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Roll Cages - are high specs necessary?
I have often wondered why some regs insist on CDS tubing and non- welded bends for roll cages as I think the spec is over the top.
To my mind a cage built of normal welded tubing would be well up to most requirements - especially as it is normally bolted and/or welded to and
already welded structure and most things fail at their weakest point - ie the structure its fixed to or the fixing.
Also all bracing bars are welded to it so there's another weak point.
So bearing in mind that:
1/ In a roll over most loads are pretty transient and not very high so fancy tubing spec is hardly justified.
2/ In a T-bone collision - most probably the worst case scenario for a racing accident the loads are normally straight into bracing bars that are
welded onto the main cage and even then loads are limited by the sideways displacement of the vehicle. In this case the fancy bent main bar has
little loading.
3/ Welding and fabricating many safety critical items such as suspension brackets, chassis etc are subject to significant cyclical loads that roll
cages do not experience is OK
I ask - why the fancy spec for roll cages?
Or is it just to give us and regulators a false sense of security!
In other words - if you are good enough to fabricate a car from scratch and run it without a roll cage why aren't you good enough to fabricate a
roll cage from the same materials with the same processes?
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Mr Whippy
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| posted on 30/10/08 at 11:43 AM |
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just have a look on you-tube at some of the more spectacular catherine wheel like rollovers and I think you'd want the best, the violence of
some of these crashes is quite amazing even a surprisingly low speeds.
I'm more impressed at how the cages take what they do bth, was watching some offroad plunges yesterday and 5 gear did a rollover test on a range
rover, it took quite a pounding at just 40mph 
[Edited on 30/10/08 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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mookaloid
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| posted on 30/10/08 at 12:02 PM |
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I think I'd want a cage which was up to the job.
It amazes me how people - I have to say a lot on here - have rollover hoops which are lower than the tops of their heads
Obviously in the case of a roll you want to be able to be upside down with out your head hitting the ground - this usually means that the bar should
be significantly higher than the top of the drivers (or passengers) head.
The cage is there for when everything else goes wrong so it needs to be good.
"That thing you're thinking - it wont be that."
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Mr Whippy
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| posted on 30/10/08 at 12:05 PM |
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quote:
Originally posted by mookaloid
I think I'd want a cage which was up to the job.
It amazes me how people - I have to say a lot on here - have rollover hoops which are lower than the tops of their heads
Obviously in the case of a roll you want to be able to be upside down with out your head hitting the ground - this usually means that the bar should
be significantly higher than the top of the drivers (or passengers) head.
The cage is there for when everything else goes wrong so it needs to be good.
 how true, the ones that really make me laugh are when they seem to have forgotten the height of the crash helmet...
Fame is when your old car is plastered all over the internet
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Agriv8
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| posted on 30/10/08 at 12:12 PM |
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<--------------
even though it may look a little strange
<--------------
and it is there to do a job not be a fashion accesory. I could not agree more
quote:
Originally posted by mookaloid
I think I'd want a cage which was up to the job.
It amazes me how people - I have to say a lot on here - have rollover hoops which are lower than the tops of their heads
Obviously in the case of a roll you want to be able to be upside down with out your head hitting the ground - this usually means that the bar should
be significantly higher than the top of the drivers (or passengers) head.
The cage is there for when everything else goes wrong so it needs to be good.
Taller than your average Guy !
Management is like a tree of monkeys. - Those at the top look down and see a tree full of smiling faces. BUT Those at the bottom look up and see a
tree full of a*seholes .............
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smart51
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| posted on 30/10/08 at 12:30 PM |
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Am I the only one then to be "amused" by the fact that 45mm diameter 3mm wall thickness seamless tube is "essential" for
safety, even though it is welded to 25mm 16 SWG ERW tube underneath.
No-one has explained to my satisfaction why you can't make the top out of the same stuff as the bottom.
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Mr Whippy
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| posted on 30/10/08 at 12:38 PM |
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quote:
Originally posted by smart51
Am I the only one then to be "amused" by the fact that 45mm diameter 3mm wall thickness seamless tube is "essential" for
safety, even though it is welded to 25mm 16 SWG ERW tube underneath.
No-one has explained to my satisfaction why you can't make the top out of the same stuff as the bottom.
it's simply due to the bar having to span a large distance without much support. Unlike the braced chassis frame. You are meant to weld the
rollbar onto large thick plates to spread the load over the chassis anyway.
Fame is when your old car is plastered all over the internet
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mookaloid
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| posted on 30/10/08 at 12:56 PM |
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quote:
Originally posted by Mr Whippy
quote:
Originally posted by smart51
Am I the only one then to be "amused" by the fact that 45mm diameter 3mm wall thickness seamless tube is "essential" for
safety, even though it is welded to 25mm 16 SWG ERW tube underneath.
No-one has explained to my satisfaction why you can't make the top out of the same stuff as the bottom.
it's simply due to the bar having to span a large distance without much support. Unlike the braced chassis frame. You are meant to weld the
rollbar onto large thick plates to spread the load over the chassis anyway.
Also the cage is likely to be subject to high direct impact forces on a small area where as much of the initial impact on the chassis in a heavy roill
will be absorbed in the ripping off of suspension components and distributed throughout the chassis
..........I would imagine
I am also pleased to say in addition to the people who have too low roll over hoops there are also a good handful who have good sized
ones..........ooh err
Cheers
Mark
"That thing you're thinking - it wont be that."
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blakep82
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| posted on 30/10/08 at 12:58 PM |
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lol
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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indykid
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| posted on 30/10/08 at 01:07 PM |
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i've got a good sized one too. it reaches all the way round infront of my head!
tom
[Edited on 30/10/08 by indykid]
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Mr Whippy
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| posted on 30/10/08 at 01:13 PM |
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quote:
I am also pleased to say in addition to the people who have too low roll over hoops there are also a good handful who have good sized
ones..........ooh err
Cheers
Mark
you have a hoop? bit impractial...
Fame is when your old car is plastered all over the internet
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Ivan
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| posted on 30/10/08 at 01:17 PM |
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So far lots of replies around "wanting the best" but none about by how much it is the best or how justified it is.
For instance I think that in SA many are made of welded bends and tubing (must be because I get blank looks from steel suppliers and recommended cage
manufacturers when I ask for CDS tubing ) and they don't fail either in accidents. And our accidents are just as good (bad) as anyone
else's
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Mr Whippy
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| posted on 30/10/08 at 01:25 PM |
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quote:
Originally posted by Ivan
So far lots of replies around "wanting the best" but none about by how much it is the best or how justified it is.
For instance I think that in SA many are made of welded bends and tubing (must be because I get blank looks from steel suppliers and recommended cage
manufacturers when I ask for CDS tubing ) and they don't fail either in accidents. And our accidents are just as good (bad) as anyone
else's
you use steel? whats wrong with bambo and rope?
Fame is when your old car is plastered all over the internet
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John Bonnett
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| posted on 30/10/08 at 01:30 PM |
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This thread seems to be running in parallel with the one posted by maartenromijn in the Chassis category. The respective merits of both one piece and
fabricated hoops have been well discussed on his thread but at the end of the day, we are free to make our own choice which is nice in a world where
more and more decisions are made for us.
You have no legal requirement (in the UK) to have a rollover bar at all so there is a big choice from nothing to the best which in my view will be the
specification laid down by the FIA. In the end as with many things it's probably a question of what you feel comfortable with in terms of cost
and specification.
John
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Ivan
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| posted on 30/10/08 at 01:36 PM |
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quote:
Originally posted by John Bonnett
In the end as with many things it's probably a question of what you feel comfortable with in terms of cost and specification.
John
John I agree entirely with you - I just wonder if there is any significant difference in strength between the two lb for lb so that I can make a well
informed decision.
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maartenromijn
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| posted on 30/10/08 at 01:39 PM |
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As per topic yesterday ( http://www.locostbuilders.co.uk/viewthread.php?tid=99610 ) we concluded that CDS bent roll-bars are stronger than fabricated
rollbars. It is best, when you have the choice, to opt for the strongest construction in the interest of your own safety.
I do agree with you that it is hard to tell which strength rollbar would be necessary. I think it greatly depends on your own risk assesment. How is
your driving style, in what kind of traffic. Nobody can tell before the accident if the rollbar is strong enough. If you have bad luck, you'll
hit a lamp-post as well.
[Edited on 30/10/08 by maartenromijn]
BLOG: http://thunderroad-super7.blogspot.com/
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blakep82
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| posted on 30/10/08 at 01:42 PM |
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soooo, if you were in a crash, with lots of rolling, landing on the roof, on the sides etc, which of the 2 underneath would you rather have a crash
in?
 
Description
CDS is stonger than ERW. its a fact. yes ERW may well be up to the job, but do you really want to wait til you hit the ground really really hard
upside down to find out?
ERW is likely to split, weakening the tube and then on the next bump on the roof, it'll bend, and your head hits the ground.
CDS holds its structure at much higher impact loads.
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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maartenromijn
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| posted on 30/10/08 at 01:49 PM |
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I'd rather crash in the yellow one. Matter of style....
Your project looks good btw. Have you designed the chassi yourself? Does it have 7-style geometry underneith?
BLOG: http://thunderroad-super7.blogspot.com/
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Mr Whippy
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| posted on 30/10/08 at 01:55 PM |
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saying that dude...
 
Rescued attachment truck.JPG
Fame is when your old car is plastered all over the internet
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Ivan
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| posted on 30/10/08 at 01:55 PM |
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Just as an aside, and I know that this has little to do with the topic - you can have too strong as well, which is exactly why car manufacturers build
in deformation into their structures - and no, I'm not saying that roll bars shouldn't be as strong as possible, what I am saying is that
if you intend to drive in circumstances that will put your roll cage to the test you better make sure that your other safety equipment is designed
around saving you from the type of brain and neck injuries that too rapid a deceleration due to too rigid structures will impart on you. (Remember
Senna)
In fact I remember reading somewhere that one of the reasons for the great reductions in F1 driver injuries with the move from steel to fibre
structures was the greater controled deformation in an accident that the fibre structures gave. i.e - controlled deformation good - too much rigidity
bad.
I think that NASCAR has similar experience.
[Edited on 30/10/08 by Ivan]
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lsdweb
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| posted on 30/10/08 at 01:58 PM |
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When the car's gone past the point of no return and just about to flip onto its roof, you'll be glad you fitted the best! Been there
(brand new Mini shell with full Rollcentre cage) and glad I'd spent the months to fit the cage!
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blakep82
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| posted on 30/10/08 at 02:00 PM |
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quote:
Originally posted by Mr Whippy
saying that dude...
yeah, i haven't bought those bar yet, but they will be there!
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Mr Whippy
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| posted on 30/10/08 at 02:06 PM |
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quote:
Originally posted by blakep82
quote:
Originally posted by Mr Whippy
saying that dude...
yeah, i haven't bought those bar yet, but they will be there!
cool just checking , looks very impressive btw 
quote:
Originally posted by Ivan
Just as an aside, and I know that this has little to do with the topic - you can have too strong as well, which is exactly why car manufacturers build
in deformation into their structures - and no, I'm not saying that roll bars shouldn't be as strong as possible, what I am saying is that
if you intend to drive in circumstances that will put your roll cage to the test you better make sure that your other safety equipment is designed
around saving you from the type of brain and neck injuries that too rapid a deceleration due to too rigid structures will impart on you. (Remember
Senna)
Most full cages do not extend to the front off a car and as you say that would be a bad idea anyway. Usually the speed that a car falls on its roof is
not all that great, nothing like hitting a wall and it's unlikey it would help if you went roof first into a tree, but there is so little room
for any deformation before it kills you that the best thing is to make it not bend.
[Edited on 30/10/08 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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maartenromijn
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| posted on 30/10/08 at 02:08 PM |
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quote:
what I am saying is that if you intend to drive in circumstances that will put your roll cage to the test you better make sure that your other safety
equipment is designed around saving you from the type of brain and neck injuries that too rapid a deceleration due to too rigid structures will impart
on you.
Everybody has to decide for himself what amount of risk is justifiable. Where to drive and in what circumstances.
Bottom line is: when you have the choice, fit the best you can.
BLOG: http://thunderroad-super7.blogspot.com/
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blakep82
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| posted on 30/10/08 at 02:10 PM |
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quote:
Originally posted by maartenromijn
I'd rather crash in the yellow one. Matter of style....
Your project looks good btw. Have you designed the chassi yourself? Does it have 7-style geometry underneith?
<--- its one of them
nooo, didn't design it myself. its an ex race car. similar suspension etc to a 7 though, but uses a watts linkage at the back.
[Edited on 30/10/08 by blakep82]
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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