• Registered: 2020-12-10
  • Posts: 26

Topic: c4 roll cage guidance

I’m building my dream, the greatest sports in automotive history, the mid year c4 corvette!

Roll cage question.  I want to pass tech without any problems.  The convertible c4 mounting possibilities are not like any of the pics.  The roll hoop behind the driver is the challenge.  The strongest part of the convertible car is the steel wall behind the seats.  It attaches directly to the rear frame rails that are also unusual because of their height with respect to the driver.  The strongest place to attach appears to be to the top wall behind the seats with a large plate added down the wall.  The plate would also support the side impact bars.  I found a similar set up that appeared to be approved for 'that other series' but I want to make sure it would also be Lemons compliant. 

Top pic was approved by 'that other series'.  Bottom pic is what we are planning, but with the addition of a large 1/8 in plate covering the top and traveling down below the lower side impact beams.  Any thoughts ?


https://i.ibb.co/r4YCyrq/0513.jpg

https://i.ibb.co/RTPQfYV/Screenshot-2023-06-09-at-9-19-40-PM.png

  • From: SF BayArea/Land of Enchantment
  • Registered: 2012-01-22
  • Posts: 903

Re: c4 roll cage guidance

Your best bet would be to contact 'The Evil One' aka John Pagel, head of technical inspections for Lemons.He has experience caging these things,and is really an alright human being.Contact him before you go any farther.Send him photos and listen to the wisdom he will give...   pagel@24hoursoflemons.com

45+x Loser.....You'd think I would learn......
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  • Registered: 2020-12-10
  • Posts: 26

Re: c4 roll cage guidance

Thanks, email sent

  • Registered: 2020-12-10
  • Posts: 26

Re: c4 roll cage guidance

Moving forward as planned.  Thanks

  • Zacks
  • Ripened Lemon
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  • Registered: 2022-10-17
  • Posts: 111

Re: c4 roll cage guidance

Dunno about rules ect but logically for safety:

Since the door bars appear to not be connected to the main hoop, in the event of a side impact the force would be transferred to the unibody through the spreader plates.  Is there a risk of shearing here?  If the unibody is thin sheet metal (vs multiple layers of structural sheet metal)  You could consider adding a crossbar from left to right door bars to brace against crushing in side impact

Once again not talking about the actual rules, just logic.  My understanding is you can add bonus stuff to the cage and not just have minimum pieces of flare.

  • From: Tustin, CA
  • Registered: 2010-12-30
  • Posts: 3,275

Re: c4 roll cage guidance

Zacks wrote:

Dunno about rules ect but logically for safety:

Since the door bars appear to not be connected to the main hoop, in the event of a side impact the force would be transferred to the unibody through the spreader plates.  Is there a risk of shearing here?  If the unibody is thin sheet metal (vs multiple layers of structural sheet metal)  You could consider adding a crossbar from left to right door bars to brace against crushing in side impact

Once again not talking about the actual rules, just logic.  My understanding is you can add bonus stuff to the cage and not just have minimum pieces of flare.

The problem with a C4 is that a lot of the structure you see in the pix isn't steel.  In the 2nd pic, the vertical piece where the main hoop is landed and the section of tube he's holding is touching is structural steel along with the sill (front legs of the cage will need to land on a plinth attached to the side/vertical portion of the sill as the floor isn't steel) but most everything else around that is not steel.  If you land the top door bar on the main hoop, you end up with door bars at shoulder level.  If you put a crossbar between left/right door bars then your team needs to be very short as the seat will want to be all the way back to that bulkhead for most drivers.  This just isn't a particularly easy car to cage and the OP is wise to consult with Pagel on this as he has caged these before.

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  • Registered: 2020-12-10
  • Posts: 26

Re: c4 roll cage guidance

I didn't want to share much about our car before the race, but with people helping me with guidance, here is our progress.

https://i.ibb.co/zXX4RsJ/Screenshot-2023-06-13-at-9-17-50-PM.png
upload

https://i.ibb.co/Br6PBTX/Screenshot-2023-06-13-at-9-22-01-PM.png
upload

https://i.ibb.co/ZBgn6QJ/Screenshot-2023-06-13-at-9-22-38-PM.png
upload

  • From: Santa Cruz
  • Registered: 2020-11-06
  • Posts: 10

Re: c4 roll cage guidance

What size and type of steel tubing did you choose?  The C4 is listed at 3,239 pounds, but I'm not sure if the removal of windows, carpet, etc. brings the weight so far below 3,000 pounds that there really isn't a question about which size is required.

9 Reply by CWracer (edited by CWracer 2023-06-26 12:08 PM)

  • Registered: 2020-12-10
  • Posts: 26

Re: c4 roll cage guidance

We will be under 3000 lbs.

  • Registered: 2009-08-28
  • Posts: 606

Re: c4 roll cage guidance

This is basically what we did when we made our C4 for Lemons (Tiger Strip 38). 

I DID check with Pagel to make sure it was OK to do this (you should too).  He gave me the thumbs up, the car passed tech in 2 other series and Lemons with no problem. 

Best of luck!

Team Sucker Punch: Winner Class B Doing Time at Joliet 2023 Autobahn ,Winner Org Choice award Were the Elite Meet to Cheat 2015
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Chevy Corvette 1984......and still racing!
  • From: Northeast PA
  • Registered: 2020-12-02
  • Posts: 16

Re: c4 roll cage guidance

It’s a bit late but there is also structure in the door jamb that you could use to land the door bars but would require removal of some of the fiberglass. Don’t know if it’s applicable in your case but just some info for anyone else playing around with C-4’s. If I ever figure out how to post an image, I’ll add one later………