Question on Lexan Thickness and OEM Door bars

[Magus2727]

Lexan Thickness:

I searched and could not find anything in the rules or specific to ST5/6 (I participate specifically in TT6) about a thickness for the Lexan/Polycarbonate.  6.1.4 - 3 specifies that you can:

The following are permitted allowances/modifications for vehicles taking the Modification Factor assessment for “BTM Aero”: 3) Lexan front, rear, and rear side windows without uncovered holes

But nothing NASA published specifies a minimum thickness.  There were some posts dated a few years back that asked this question and rules from other bodies (PCA and SCCA) were brought in but nothing from NASA.  TT rules only mention that fixed front passenger and driver windows are not allowed.  ST rules have some more information but just goes into use of Lexan while still tasking the BTM modification factor.    Is there a NASA Rule on the thickness of a rear or rear side replacement of Lexan/Polycarbonate?  I have searched the rules (using the newest 2022 ones) and have not been able to find anything.

 

Door Bars:

I am installing a cage on my vehicle and am working on removing weight in the areas that are now no longer needed due to having a cage.  One of the things I was reading in the general CC&R's was:

15.6.12 Door Bars / Side Impact Protection At least two (2) door bars on the driver side and one (1) door bar on the passenger side are required in all vehicles. Note- an “X” design counts as two bars. Unless superseded by class rules, modifications to any non-chassis structure (such as door panels, inner door sheet metal, windows, door internals, etc.) may be made to accommodate any allowed door bar configuration. However, removal of material and / or modifications is limited to 1) the least amount to accommodate the door bar(s), and 2) can serve no other function. Holes, or notches, in the door jamb (B-pillar) are permitted to accommodate door bars.

The area I have question about is the bit I added in bold.  This reads to me that I am unable to completely "skin" the OEM door i.e. remove the internal sheet metal and the side OEM crash brace unless it interferes with the roll cage.  As I have walked around the paddock I have seen MANY if not ALL cars that have the two side bars operate with a completely "gutted" door leaving only the outside sheet metal.  In the https://nasaspeed.news/tech/fabrication/gutting-a-door/ it shows the full removal with out measuring where it may interfere with the "Petty" bars.  If the cage I have has the two door bars can I remove the factory side impact brace? 

Thank you!

 

  

[Greg G.]

There are no longer any rules in the CCR or ST rules regarding thickness of Lexan.  If you don't use thick enough Lexan or enough supports on the rear, you may get the window buckling in and out (since venting of the window and cockpit are not permitted in ST4-6). 

The ST Rules do not require you to keep the door internals or inside metal intact, so they supersede the CCR.  NASCAR style door bars on the cage will most likely require the removal of the OEM crash brace.  A lot of folks will still leave that brace if possible to give the door a bit more strength.  Hank Padilla would have to answer if you can remove it if you don't have NASCAR style door bars, because it is really a Tech issue more than a class rules issue. I've pointed him to this thread.

[Hank P.]

Hi, some class rules do not allow removal of the side impact beams; as Greg states this is not the case for ST so it is ok to remove the side impact beam to accommodate your extended Nascar-style door bars.

Regarding your observation that some cars have more of the door structure removed than is specifically required for fitment of their extended Nascar-style or extended-X-style door bars, some regions may allow this as long as it does not present a safety issue. However, if using straight/non-extended door bars, then per the CCR removal of the door sheetmetal is not allowed if it is not necessary to accommodate the door bar design.

Hank
National Chief of Tech

[Magus2727]

Thank you for answering this and clarifying.