Forged Performance: SPOHN's Custom FP Spec 4-Point Cage

Originally Posted by wstar

@Forged,

Do you mind if I pick your brains a little bit on the design here? I'm in a similar boat w/ Chris on current status/requirements and looking to put in a similar 4-point in the near future. Forged is a bit of a drive for me though (~13 hrs each way), so I'll probably use a local shop (undecided who yet). I've been trying to at least mostly sort through the design issues first on my own, so that I know what I'm talking about and what is or isn't acceptable when I start talking design with the shop (who I hope knows more than I do anyways, heh).

1) What was the logic on choosing this particular DOM size (1.75 x .095), does that just happen to hit a sweet spot for being legal for this car's usual class in a couple of different rule sets or other?
Minimum tube diameter and wall thickness is mandated by the various road racing sanctioning bodies such as the SCCA, NASA, and Grand Am. We look at the final projected race weight and select the tubing accordingly. Vehicles that race at 2500lbs or greater require a minimum 1.75 X .095 tubing to be used.

2) Is it possible to take the main hoop ends all the way to the lower floorboard as a design option when doing this, or does that just end up being a much weaker mountpoint than the obviously-strong spot you put them on that crossmember? Are there other pros/cons between those two spots, assuming the lower one is even viable?
The cage is tied into the much stronger frame rail, rather than the floor board. You always should strive to anchor your cage to a frame rail or major chassis support structure.


3) What's the pros/cons on going with the harness bar offset to the rear like Chris's vs having it inline with the main hoop? I imagine your design is stronger (because in-line one of the two bars has to be cut and put back together), but is there more to this decision?

The main purpose is to have more seat travel, and more room to loop and angle your harnesses. We take a look at seat, and driver location, and many other factors before making the final decision. It's more work to do the angled harness bar but we think it's the right thing to do for maximum versatility.



Oh and I guess (4) if you happen to know of a shop that's closer to Houston you'd recommend, I'd love to hear about it, would make my search easier
Many of our customers live further away than you...come on down.