Roll cage for TT - options?
#22
I have been looking at rules for FIA roll cages. It appears that they spec 1.75" x .095 tubing for the main components of the cage and allow for 1.50" x .095 for the support bars such as a the backstays, diagonals and doorbars.
Am I reading that correctly? I haven't found any that specify tubing size by the weight of the car like some organizations do.
Am I reading that correctly? I haven't found any that specify tubing size by the weight of the car like some organizations do.
#23
I have been looking at rules for FIA roll cages. It appears that they spec 1.75" x .095 tubing for the main components of the cage and allow for 1.50" x .095 for the support bars such as a the backstays, diagonals and doorbars.
Am I reading that correctly? I haven't found any that specify tubing size by the weight of the car like some organizations do.
Am I reading that correctly? I haven't found any that specify tubing size by the weight of the car like some organizations do.
Up to 1500 lbs 1.375” x 0.095” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical), DOM, or Docol R8 (only) 1.500” x 0.080” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical), DOM, or Docol R8 (only) RACING AND COMPETITION 47
1501 - 2500 lbs 1.500” x 0.095” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical), DOM, or Docol R8 (only) 1.500” x 0.120” ERW* (No issuance of log books for cars with ERW cages) *Note- Specifications listed only for reference for inspection of grandfathered vehicles.
2501 - 3000 lbs 1.500” x 0.120” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical), DOM, or Docol R8 (only) 1.750” x 0.095” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical), DOM, or Docol R8 (only) 1.750” x 0.120” ERW* (No issuance of log books for cars with ERW cages) *Note- Specifications listed only for reference for inspection of grandfathered vehicles.
3001 - 4000 lbs 1.750” x .120” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical), DOM, or Docol R8 (only) No ERW allowed. Over 4000 lbs 2.000” x 0.120” Seamless Alloy (4130), Seamless mild steel (CDS Mechanical), DOM, or Docol R8 (only) No ERW allowed.
I'm sure SCCA and other commonly-referenced rulebooks are similar.
The references above to "FIA" spec are mainly the use of IMSA style pyramid or 3D X doorbars and the A pillar reinforcement tubes.
#26
Yes, all the org’s I have seen specify the size of the tubing based on the weight of the car. I find it odd that the FIA only gives 1 spec for tubing size that I can find.
What at is the general thought/ consensus on the additional A pillar reinforcement bars and the pyramid x shaped door bars? Are they considered as strong or stronger than the NASCAR style bars?
#27
Yes, all the org’s I have seen specify the size of the tubing based on the weight of the car. I find it odd that the FIA only gives 1 spec for tubing size that I can find.
What at is the general thought/ consensus on the additional A pillar reinforcement bars and the pyramid x shaped door bars? Are they considered as strong or stronger than the NASCAR style bars?
#29
Keep in mind that FIA bars take a massive amount of room from the door opening and that might not work for many drivers for quick exit purposes.
To avoid that issue in Morpheus, I replaced the tubes with a 3D curved gusset which is a great way to spend 20+ hours fabricating one piece of sheet metal, even if you're well versed at this -
#30
As Andrew observed, if you are not otherwise limited by rules, go big. Traditional Spec Miata cages are floor mounted only. They provided only the minimal roll over and intrusion protection. Beyond that, they offer only the minimal amount of torsional stiffness increase compared to a fully integrated cage. NASA ST rules allow almost a full FIA cage in ST5. In Supermiata, we are adopting more open rules for cages even in S2 (140whp). S1 goes a step further by allowing a full integrated FIA cage with extensions to the front shock mounts. The merits of a 12+ pt cage attached to the firewall and door jambs go far beyond mere intrusion protection but that should be enough. In most cases, the cost and weight only increase slightly and the car is future proof for additional power/grip/ aero loads.
#31
Additionally is important to remember that the Miata is not a strut car so the actual shock tower doesn't have that much load going through it. The highest forces are going into the subframe mounts which are those two big studs that poke out the bottom of the frame rail. Those forces are trying to twist the front of the car and deflect the frame rails out of the same plane. So that's really what you are trying to reinforce, box or triangulate. Triangulation preferred as it uses a lot less material than a box, for a given stiffness.
From a safety standpoint it is intrusion. Like most small cars keeping the front wheel and suspension out of the driver's footwell in a major frontal impact is a challenge. A simple triangulated brace anchored at the door bar foot and a little higher up and extending forward to the stiffest part of the firewall helps hugely in this regard.
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