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F.5.9 Main Hoop Braces
F.5.9.1 Main Hoop Braces must be constructed of closed section steel tubing meeting F.3.2.1.h
F.5.9.2 The Main Hoop must be supported by two Braces extending in the forward or rearward
direction, one on each of the left and right sides of the Main Hoop.
F.5.9.3 In the side view of the Frame, the Main Hoop and the Main Hoop Braces must not lie on the same side of the vertical line through the top of the Main Hoop.
(If the Main Hoop leans forward, the Braces must be forward of the Main Hoop, and if the Main Hoop leans rearward, the Braces must be rearward of the Main Hoop)
F.5.9.4 The Main Hoop Braces must be attached 160 mm or less below the top most surface of the Main Hoop The Main Hoop Braces should be attached as near as possible to the top of the Main Hoop
F.5.9.5 The included angle formed by the Main Hoop and the Main Hoop Braces must be 30° or more.
F.5.9.6 The Main Hoop Braces must be straight, without any bends.
F.5.9.7 The Main Hoop Braces must be:
Securely integrated into the Frame
Capable of transmitting all loads from the Main Hoop into the Major Structure of the Chassis without failing
Explanation
F.5.9.1 Main Hoop Braces must be constructed of closed section steel tubing meeting F.3.2.1.h
The Main Hoop Braces have to be made of closed section metal tubing (i. e. tubes that have continuous sidewalls) and it also must match the requirements in the tubing chart from F.3.2.
F.5.9.2 The Main Hoop must be supported by two Braces extending in the forward or rearward
direction, one on each of the left and right sides of the Main Hoop.
The Main Hoop has to be supported by bracing tubes. These tubes can be located in front or behind the Main Hoop depending on other physical and rules constraints. There has to be a brace on both sides of the Main Hoop.
Our Main Hoop has braces that extend towards the back of the car.
I've drawn in hypothetical front braces (probably not rules compliant) just to show what the forward extending braces look like.
F.5.9.3 In the side view of the Frame, the Main Hoop and the Main Hoop Braces must not lie on the same side of the vertical line through the top of the Main Hoop.
(If the Main Hoop leans forward, the Braces must be forward of the Main Hoop, and if the Main Hoop leans rearward, the Braces must be rearward of the Main Hoop)
This one is easier to draw than it is to explain, but the rule is basically saying that from a side view, the Main Hoop and the Main Hoop Braces need to be on opposite sides of an imaginary vertical line that passes through the top of the Main Hoop.
Here is a picture of our chassis. It is kind of ambiguous how we follow this rule because our Main Hoop follows the line that is the threshold for the rule. I think a vertical Main Hoop is acceptable but is at the limit of what is acceptable.
Here are some hypothetical examples that make the rule a little more clear:
In this example, the Main Hoop is on the opposite side of an imaginary line passing through the top of the Main Hoop than the Main Hoop Brace, which is rules compliant.
In this example, the Main Hoop and the Main Hoop Brace are on the same side of the vertical line passing through the top of the Main Hoop, making it not rules compliant.
F.5.9.4 The Main Hoop Braces must be attached 160 mm or less below the top most surface of the Main Hoop The Main Hoop Braces should be attached as near as possible to the top of the Main Hoop
They want the Main Hoop Braces to be as close as possible to the top of the Main Hoop, probably for safety reasons because it is really important that the Main Hoop not budge in case of a rollover. Specifically, the Main Hoop Braces have to be attached less than 160 mm from the top of the Main Hoop, and it tends to be convenient to attach them at the bends of the hoop anyway (even though this isn't technically required per F.5.2.
It is not super clear if the distance between the Main Hoop Brace and the top of the Main Hoop is measured from the top of where the Main Hoop Brace is connected, or somewhere different. The safeest bet is to have the entirety of the Main Hoop brace connection within 160 mm of the top of the Main Hoop.
Here is a picture from our 2023 SES that shows how we follow this rule. They measured from the bottom connection of the Main Hoop Brace to the top of the Main Hoop.
F.5.9.5 The included angle formed by the Main Hoop and the Main Hoop Braces must be 30° or more.
The angle that the Main Hoop and the Main Hoop Brace connection form should be at least 30 degrees.
The angle between the Main Hoop and the Main Hoop Brace has to be at leaset 30 degrees.
<< Here is the image from our 2023 SES that shows how we follow this rule.
Image from the rules
F.5.9.6 The Main Hoop Braces must be straight, without any bends.
The Main Hoop Braces can not be bent tubes.
<< Straight with no bends
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