Roll Cage question .......

I totally agree with you Randy, but these things need to be said and risks assessed. Neither of these cars rolled over , so it has to be asked if the "cages" are not a greater danger than not having one at all. As I stated before, I will not drive or passenger in a 40 if it has any exposed steel work inside the cell that we sit in.
 
I have owned/raced Datsun 240z which don't have a lot of room for a full cage. Your head is very close to roof/door bar and depending on the cage installation and your height I have seen drivers helmets rub on that bar during a race let alone an impact. I have owned/raced a classis mini also these are a small car but have more room that a Datsun 240z for a full cage...but again it is still very close to the occupants.

A GT40 has much less room that the 2 vehicle mentioned above. When I start my GT40 build it will NOT be getting a cage or any exposed metal structure inside the occupants area. Especially after reading the pdf Frank shared and other comments/feedback in the thread.

I consider driving these older designed vehicles much like riding a motorcycle on the road. Not ideal to have a crash in period.

Modern cars have so much safety features i believe it is robbing us of correct driver education/skill set. People almost think they will be ok in an accident due to all these safety features. But the safest way to avoid injury is drive to the conditions/cars/drivers ability and avoid a crash in the first place.

Be safe out there and respect other road users they have families too and want to get home to them.

Yes at times I ride my motorbike like a loon when the conditions are right ;) but I also ride daily so know the risks I am putting my self in.
 
Really interesting thread - I had an intention to build a roll cage to my GT40 but as it will used mostly on road and 1-2 trackdays/year I hesitate on having a roll cage ;)

Thinking of having a roll bar as far rear/up behind the seats but skip the front roll bar and the connecting bars in the middle of roof.
Maybe it would be good to have some smaller/lighter reinforcement to support front windshield weight.
Good or bad ideas?
 
Really interesting thread - I had an intention to build a roll cage to my GT40 but as it will used mostly on road and 1-2 trackdays/year I hesitate on having a roll cage ;)

Thinking of having a roll bar as far rear/up behind the seats but skip the front roll bar and the connecting bars in the middle of roof.
Maybe it would be good to have some smaller/lighter reinforcement to support front windshield weight.
Good or bad ideas?
Depending on whose bodywork you use there may already be some limited metalwork embedded within the spider.
 
Don't know how you would create a windshield support structure that wouldn't be prone to bending back towards the occupants in a wreck. This is the primary issue with the GT40 cages to begin with - no direct support from windshield header to roll hoop, because of door shape. Safer bet is probably ensure that your head lies below the plane defined from top of roll hope to the first structural element ahead of the passenger cell - likely the dash hoop. Same criterion used in open cockpit cars.
 
Really interesting thread - I had an intention to build a roll cage to my GT40 but as it will used mostly on road and 1-2 trackdays/year I hesitate on having a roll cage ;)

Thinking of having a roll bar as far rear/up behind the seats but skip the front roll bar and the connecting bars in the middle of roof.
Maybe it would be good to have some smaller/lighter reinforcement to support front windshield weight.
Good or bad ideas?
Man you need to speak with is Frank Catt......

Also as MarkR mentioned there may be some limited metalwork embedded in the spider (depending on whose it is) and if there isn’t it may be quite easy yo do it yourself once the body with windshield is in position.
 
The metalwork that's included I believe is more to stiffen the side of the windscreen aperture to prevent flex and subsequent cracking of the glass.
It's not a structural safety component and is fully embedded into the fibreglass.

To my way of thinking, the difference is that, an impact directly onto the top edge or side edge of the windscreen is going to continue with little resistance and the offending object will continue to hit the occupant or not depending on trajectory.
If that brings with it a 13mm square section of aluminium (this is just a visual guesstimate), some fibreglass and a piece of windscreen then it's not going to hurt any more then bringing fresh air along.

The difference with adding into the cockpit a 38mm (or similar) piece of steel work that the steel work is now closer to your head than the screen behind it. The other consideration with a rigid piece of steel is that, depending on the impact dynamics, it may crush back along its length giving your head no opportunity to be "pushed aside" by the encroaching component.
The other issue with a front hoop is the way it can distort as a result of any hard frontal impact. When it distorts who knows exactly which way it will move but the fleshiness of the human body it reaches won't stop it. For example, a frontal hit on the OS leg of the front hoop will drag the NS beam back and down!
 
From the various reading and photos of accidents involving GT40’s with roll cages I made the decision and removed mine from my build. It’s simply too close for comfort for my liking. Aside from the danger posed by the proximity of the roll cage bars to the occupants heads, the bolt on type of roll cages will always have a very weak connection at the flanges where the bolts go through - anyone who knows about structural angineering and trasmisssion of forces, stresses, moments and torque will know that these type of connections will be the weak spot so the structure will deflect under the smallest of knocks in the right place.
Unless you can figure out a way of building a roll cage not using bolt on method but welded and starting from say higher up (not the lower connecting point of the chassis) and also work out how to keep the occupants heads away from the bars then you’ve got yoursleves a winner! Best way would be to somehow incorporate the roll cage into the spider section which would mean making something simlar to the original spider section. Problem is that each of our builds (even from same supplier) end up so considerably different that this part could probably not be done properly until the build is complete and all body panels in place so as to form the spider to fit perfectly with the front/rear clips and doors/sills.
Yes the metalwork in the spider windshield aperture would not be structural but only for stiffening the opening for the windshield.
Just my thoughts........
 

Randy V

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Lifetime Supporter
Don’t forget that a proper laminated windshield will add an incredible amount of strength to the spider if it is installed with a Urethane bond as are literally every production windshield is today. The center tie-bar between the front and rear of the spider would certainly play a major role in the support of the windshield.
 
Don’t forget that a proper laminated windshield will add an incredible amount of strength to the spider if it is installed with a Urethane bond as are literally every production windshield is today. The center tie-bar between the front and rear of the spider would certainly play a major role in the support of the windshield.
Hi Randy, I disagree - there's no good load path front to back on either corner of the windshield. the spider serves to stop the entire windshield hinging back at the base under a controlled and distributed load (wind). The strength the bonded-in glass provides is transverse/shear for the windshield frame, with next to no elasticity. As a wild-ass guess, a down and back force of a 1000 pounds, delivered at the top of the windshield/front of the spider would cause significant distortion, possibly failure.
 

Randy V

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Lifetime Supporter
In regard to the strength of a properly installed windshield - my son went to college to study not only automobile body design and engineering, but repair of damaged cars to restore their crash worthiness.
A primary tenet of cabin strength was that of the front and rear glass and the fact that they are an integral part of the monocoque system.
Certainly the support structure around the glass must be robust. I won’t get into the strength of stamped mild steel of the original spider vs. the fiberglass structure used by almost every GT40 manufacturer today. Either way - I think it is easy to see that a windshield bonded to the spider with automotive urethane would be far more preferred than one bonded in with simple RTV or gooey butyl..
 

Randy V

Admin
Lifetime Supporter
Hi Randy, I disagree - there's no good load path front to back on either corner of the windshield. the spider serves to stop the entire windshield hinging back at the base under a controlled and distributed load (wind). The strength the bonded-in glass provides is transverse/shear for the windshield frame, with next to no elasticity. As a wild-ass guess, a down and back force of a 1000 pounds, delivered at the top of the windshield/front of the spider would cause significant distortion, possibly failure.
Agree on the corner loads, but without a somewhat robust tie-bar between the top center of the spider and the rear, that windshield would surely collapse with little resistance. This is the point I was trying to make.
 
Came across this at the Zandvoort Historic GP 2020.
Very interresting to say at least. Guess he didn't read this topic.....
Zandvoort 2020 (1b).jpg


Zandvoort 2020 (2b).jpg



Zandvoort 2020 (3b).jpg



Zandvoort 2020 (4b).jpg


Ill guess, you'll get in, Dukes of Hazzard style....:D
In case of an accident, before you get out or.... they get you out thats the real question.

Nice to read the article again in the magazine.
 
Also you can see how the ‘X’ frames in way of the door openings sure up the front vertical bars. The problem with ’bolt in’ roll cages is that they have no support in that direction and any accident from the front or side will force those tubes into the occupants. I can’t see clearly how that roll cage is actuallhy attached and if it is welded (instead of bolted) together with these cross braces and from the looks of it more strengthing then this roll cage will form a more continuous part of the main chassis and transfer forces rather than deform to the extent of killing the ccupants. Of course it depends on the force of the accident but it will take a lot more than the bolt on roll cages which don’t have the cross bracing.......none of which (in this particular case) belies the fact that the driver would still have to be about 4 feet tall and 98 pounds just to get in and out......you couldn’t get a Daisy Duke in that one...
 

Randy V

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As a competition only cage, I like his design. Ingress/Egress is going to be tight, but doable since the driver can step over the door bars and stand on the seat - working his way down. I doubt that he’d pass a closed door 15 second egress test though...
Certainly I would not advise driving this car without padding on that cage as well as a good helmet..
 

Randy V

Admin
Lifetime Supporter
Oh and he still needs to add a diagonal brace on the main hoop.
Looks as though the mounting pads for the cage are welded to the tops of the sills...
 
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