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280Z-LS3

Plate and tube thickness guidance

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Going to start chassis stiffening and would like guidance on tube and plate thickness.  

 

My main cage will be DOM 1.75"x0.095".  I hope to be under 2800 lbs. but figured better safe than sorry.  What is minimum plate thickness for boxes that support main bar and forward a-pillar bar?  I believe 2020 SCCA rules say between 0.080" and 0.25".

 

Tube size and thickness for anything other than cage, DOM 1.5"x0.065"?

 

And thickness for the additional chassis support plates for stiffening tube?.  Some areas I am considering are from radius arm bracket to rocker panel, wrapping front strut tower to support forward frame rail and rear ward roll cage tie ins, tops of rear shock towers.

 

 

Edit:  Adding info from searches.

Roll cage mounting plate min. of 0.080" thick, no more than 100 sq.in. and no less the 9 sq.in.

 

Edited by 280Z-LS3

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In case you've not seen this, there are some great ideas here for chassis stiffening:  https://imgur.com/a/R27sh

 

Will SCCA be the sole sanctioning body for the events you plan on running (i.e. are you planning to run only SCCA-sanctioned events); and what types of events/classing do you plan to run?  Interested to follow progress on your build. 

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Thanks jhm, I have seen those pics and stealing plenty of ideas, lol.  Of particular interest is bjhines's car/cage he built back in 2006, I like his cross bar that contours firewall just below windshield.  I can just see myself wasting a bunch of tubing trying to get that bar fit properly...  I would like to have the front strut towers triangulated off that bar.  I don't plan on having a node at that point taking load back to rear strut towers because it will intrude on passenger space.  Not the best design but compromises are going to be made.  But that's a whole different conversation...

 

Since my plan for the Z is a street legal car I plan to target autocross, HPDE and maybe Time Attack.  If I decide to go deeper into competition, and have not broken too many rules with all modifications, I'd like to know my cage is legal.  But first and fore most want it provide safety.

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I too just followed the SCCA rules.  In my case 1.5"/.120" wall tubing, and .100" for all the reinforcing plates.  IIRC those specs are good up to 2800# car.  I sure as hell hope my car doesn't wind up heavier than that....but it could I guess.

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There is quite a bit of weight in the tubes. When I did mine the SCCA said they were going to change the tubing requirements, and at the time they had 1.5 x .120 and 1.75 x .090. I went with 1.75 x .120 anticipating a change to a heavier tube, but when they released the rules, they had gone the other way and the requirement was 1.5 x .095. I  haven't gone through how much weight I would have saved with 1.5 x .095, but man, I wish I had gone that way. Probably 50 lbs added, a lot of it way up high. Not good.

EDIT--I did do the 6 point main part of the cage in 1.75 x .120, then I did all of the other stiffening tubes in 1.625 x .065.

Edited by JMortensen

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