roll cage question

[janjon]

Hello Roo and all:
Got a question concerning  the secondary roll bar on my car. If you can see in the photo I'm trying like xxxx to attach, the left and right sides of the secondary roll bar extend to the back braces, up from the shoulder hoop, but between the back braces, the secondary roll bar does not exist. I have seen this in the past on other cars, if memory serves. What would be the reason for this, if indeed there is one, and is this kosher according to the rules as published? And would it represent best practices? It would seem that this would allow for a bit of "crush", but I'm not sure I see that as a good thing... helmet fit being pretty tight as-is. Any thoughts?

[hotrod316]

If you are talking about center brace between the back supports in line with the secondary hoop, on a 2.6 or 2.6a yes, (750 slower). On a 2.4c again yes  Effective: march 5, 2010 sfi 2.4c and august 2001 sfi 2.6a - it is number 2 in the sfi books
if not sorry ,
your turn Roo

[dreracecar]

Most builders use a piece of oval or streamline tubing in that area and posistion it flush with the top of the round tube.

[janjon]

 Thanks, hotrod and dre for the replies. I will get myself a copy of 2.6A for further guidance. 2.4C will never apply to this chassis. Not even in my dreams. Sub 7.50 is WAY out of reach.
 Dre, I find it interesting about airfoil tubing filling that gap, seems certainly no aerodynamic advantage to that, possibly just using up drops from wing struts to fill the gap for cool factor?
 It just seems logical to me that if the main hoop should be entire, so should the secondary hoop, from a structural standpoint, interrupted only by the existence of the back braces, and my inquiring mind still does not know what the reasoning there is.
So, again, any thoughts?

[dreracecar]

A six point cage must have a center brace between the back supports in line with the secondary hoop of the roll cage. It has nothing to do with COOL or AERO,  Because the width is smaller than the dia of the roll cage tubes and one mounts it on the high side of the support uprites it gives more clearence for the curve of the helmet between the two rear/upper roll cage supports. We have two shapes available to us, one is oval and the other is streamline, Legal streamline is approx 2" X .857 X .049 and has the tension rating equal to 1 1/2 dia round and is available thru sourses by the foot  ($21.65 per)- oval tubing has to be made by useing a press to compress the round into an oval.

Draw two circles 1.500 dia 6 inches apart, then draw a straight line across from the 12 oclock possision. Now draw another line across from the 6 oclock possision. this will give you the relationship if one uses round tubing for the cross support. Now from the top line draw another line parallel below the top line about 7/8", this will give you the effect of the oval or streamline tubing. Your helmet is now afforded the clearence between the two 1.500dia tubes and not a single contact point.

[janjon]

Thanks dre, so it's a clearance thing. However your statement that it must be there seems to contradict racecar's statement, if I understood it correctly, that it being lacking (not there) is kosher and does represent best practice??? All should become clear upon the arrival of 2.6A. I recall from the NHRA rule book that the front of the helmet must be 3" min (rearward) from the front hoop, but is there a vertical min. clearance?
John

[dreracecar]

Vertical clearence is 2"

Any chassie that must have a NHRA/SFI sticker -MUST have a tube between the uprites. Any chassie that does not have to be inspected or tagged (10.00 and slower) must have that tube in place although most local track inspectors will overlook it because the diagram in the rulebook is not detailed as much as the SFI spec book. I asked another racer about his car and the answer was that it was to save weight on the chassie to allow him to eat a double cheeseburger instead of a single.

[rooman]

Bruce (and Steve),
                         thanks for jumping in while I was otherwise occupied over the weekend.

Roo

[janjon]

Thanks, everybody, for taking the time to answer. 'Tis now clear. Crystal. Now for some Krystal. Not.
John

[hotrod316]

Roo next year DINNER on you
STEVE