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I personally chose 1.75 x 0.095 DOM MIG-welded for my Spec Boxster after consulting with Josh Lucas of Lucas Fab in Huntington Beach, who built my cage.
A spec Boxster with driver minimum weight is 2650 lbs. I weigh 180, so car minimum is 2470 lbs without driver.
PCA says for a car without driver, under 2500 lbs. requires 1.50 x 0.095 in mild steel. Given that the Boxster is only 30 lbs under that, I think it's prudent to step up to the next level. For over 2500 lbs, the PCA says 1.75 x 0.095 or 1.50 x 0.120 in mild steel.
NASA has exactly the same rules for mild steel. They're different from the PCA for 4130, but my builder does not recommend 4130 because it's more brittle (gives suddenly), even though it's stronger in the same sizes.
The SCCA says for a car of "GCR Vehicle Weight" (with driver, I think), under 2700 lbs, 1.5 x 0.095 or 1.625 x 0.080 mild steel is required. Again, since a Spec Boxster is only 50 lbs under this, I would go up to the next level, which for the SCCA is 1.50 x 0.120 or 1.75 x 0.095 or 2.0 x 0.080.
So, in summary, with all three organizations, you can technically get away with 1.5 x 0.095 mild steel, but I think 1.50 x 0.120 or 1.75 x 0.095 would be smart, since the Boxster is right on the edge of the limits.
Save weight somewhere else. You can still get to 2650 with driver.
I also had the FIA vertical bar added, after seeing how the front of a cage collapsed in a Spec Boxster roll-over accident at Willow Springs a few years ago.
In addition, I had a knee bar added and bars forward to the front shock towers.
Hope this helps,
Greg
Last edited by Greg Holmberg; 01-27-2016 at 08:25 PM.
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