Apparently not, because he chose the second worse door bar arrangement for any uni-body car. The design of a NASCAR chassis is significantly different than any uni-body design. The NASCAR chassis is designed for the "nascar door bars". Most production cars are in no way designed to accommodate the NASCAR door bars and most are at best a compromise and at worst an overweight tragedy.

If your fabricator is considering using the current mess in the car, find another fabricator.

There are a lot of different designs that people use the term "Nascar doorbars" for.

A prime example would be the guys in the Pro Drift series.

I think most use the term when talking about a double row door bar configuration extending to the outer door skin but not specifically the design used by Nascar.

I understand what he is talking about. In order for them to work the way they work with a Cup chassis, they have to be plated and tied into the chassis properly. Looking at the current structure within Bob's car, there is little to no structure to support those bars. Its doubtful the builder understands what needs to be done to make those work.

Of course my comments apply to most average roll cage builders who would put door bars on the existing structure. Guarantee they walk over to the bender, bend a couple of tubes and stick them to current a-pillar down bars and main hoop.

They put no thought into the way the loads from an impact will feed into those two completely unsupported nodes and thus cause them to collapse inward. To properly utilize the "NASCAR" bars, you would need to build what amounts to a square box around the driver and then out to both shock towers.

I have build dozens of cages and refuse to install NASCAR bars because they are not the right solution. IF NASCAR bars were the end all be all, Porsche, Ferrari, Ford, Chrysler, BMW, etc would install them on their factory engineered race cars. They don't, because they aren't the best solution.

Don't get me started on the drifty kids. They don't build cars for anything beyond show and sliding.

SCCA uses the term "NASCAR bars" not as a design term but as a descriptor for the need for two (minimum) horizontal bars:

NASCAR-Style Door Bars – If installed, shall consist of one or more sidebars that intrude into the door cavity and connect the main hoop to the front hoop.


Fabricators should absolutely consider load paths and attachments when building these, with the goal of stopping a car from intruding into the cockpit and injuring the driver.

I do not build cages (though I do have a BSMechE) so I'll defer to fabricators like Brett, but my general mindset is that the bars should be sufficiently stout not so much to stop a car from coming in, but to assist in moving the caged car out of the way of a collision, based on weight and tires used.

Toward that, SCCA is allowing and encouraging fabricators to attach the seats directly to the cage, not to the car's structure. That way, when the cage moves, the driver moves within that protective structure. That can also give fabricators some flexibility in cage-point-restricted classes (e.g., Touring, B-Spec, Improved Touring) by attaching to cage on both sides of the driver, making a mini-cell-within-the-cell.

We don't have a lot of engineers in the scrutineering pool, so a lot of the design falls on the fabricator; if it has two horizontal bars, it's a "NASCAR Bar" and will get signed off. So, choose your fabricators carefully...

Here's mine, I'm six foot, never a problem with the knee bar. MarkClick to view attachment

Working on a T45 cage by Custom Cages UK,
Attachments from rear main hoop to trailing arm, and another to shock tower, then triangulations.

another view

Is that cage above being built to a specific sanctioning body's regs? May want to review those regs. It would not be acceptable for SCCA Club Racing:

"Braces must be attached as near as possible to the top of the main hoop (not more
than 6 inches below the top), and at an included angle of at least 30 degrees."

?From your quote:
9 C. Roll Cage Bracing
1. The main hoop must have 2 forward braces extending from the hoop and attached to the frame, monocoque, or front hoop. Braces must be attached as near as possible to the top of the hoop but must not be more than 6 inches below the top and at an included angle of at least 30 degrees.

or 9.4.B1c
c. Cars must have 2 braces extending to the rear from the main hoop and attaching to the frame or chassis. Braces must be attached as near as possible to the top of the main hoop (not more than 6 inches below the top), and at an included angle of at least 30 degrees.

In a 914, Is a short rear brace to the inner frame at the top of hoop inside the cabin acceptable?

such as in:

9.4.c.2.e. On cars where the rear window/bulkhead prohibits the installation of rear braces (e.g. Honda del Sol), the main hoop shall be attached to the body by plates welded to the cage and bolted to the stock shoulder harness mounting points. This installation design must incorporate a diagonal bar connecting the top of the main hoop to the lower front passenger side mounting point (Petty Bar).


Hi, still building the cage, not building for SCCA club racing, rather tarmac rally. Will be adding braces high on the main hoop to above the seatbelt anchor bolt frame. Main hoop diagonal, harness cross brace and roof diagonal. The cage is FIA spec kit, but I've modified it so the upper main hoop stays don't travel through the rear window.

options to modify further, always good to build it for as many venues as possible, (ie the next owner)

Any suggestions appreciated, and thanks for the nudge to check roll cage rules again.

Cheers

For reference, I'm an SCCA scrutineer.

What caught my eye on this was that the rear braces do not appear to go up to within 6" of the top of the main hoop. The purpose of those rear bars is to ensure the integrity of the main hoop in case the world turns upside down on you. The braces you have there will support the bottom half of the main hoop, but that leaves the top half vulnerable to collapse.

There are two ways to resolve this:

- Run rear tubes that start within 6" of the top of the main hoop, and run the tubes through a polycarbonate rear window; see second part of GCR 9.4.c.2.e, quoted below.

- If you don't want to run a poly rear windows, then follow first half of GCR 9.4.c.2.e that you quoted above, by adding plates to attach the cage to shoulder harness mounting points and adding a Petty Bar, from the top of the cage just to the right side of the driver's head (with sufficient clearance) down to the mounting plate for the right front leg.

The first option is the more common and traditional method for "real" race cars, and allows you to continue that tube to strategic rear points on the chassis; that's the way my race car was built by Chris Foley. See attached.

But maybe it's a dual-mission car and you don't want to run poly rear glass and/or cut into the car? Then you can use a Petty bar and the additional tab mounts as required. That Bar can also be sleeved to make it removable for the dual-mission, just ensure you make some kind of padded cap to go over the studs for safety in a road accident.

GA

Just a quick follow up that I forgot to mention.

The purpose of allowing the Petty Bar and requiring seat-mount tabs, for a cage not using rear bars, is to keep the cage from "Z-ing" in the middle. This is where the top is held BACK by the upper front bars, and the middle is kept from bending FORWARD or SIDEWAYS (creating a "Z") and collapsing onto the driver. The Petty Bar is additonal lateral support so that it does not collapse sideways.

From a purely technical safety perspective, your bars in that same area as the seat harness mount do the same function. So it's not that I have a technical problem with the safety aspect, presuming you add a Petty Bar; it's just that it may not meet teh technical letter of the regs.

(I'm presuming you're also adding a diagonal and a horizontal with the plane of the mian hoop?)

Since the design does not meet the LETTER minimum of the regs, I'm not sure that field scrutineers would have the authority to approve it for SCCA. Could/might/maybe appeal to the home office for a waiver...? Clearly, I'm speaking for solely for SCCA regs (assuming someone wanted to go that way), not to the tarmac or any other orgs' requirements. - GA

Thanks Greg!

I may have been a little stubborn about the plexi back window.
Have read through a couple more regulations and I understand what you are talking about.

My cage is tacked only, waiting to get full weld after we suss out all the details of fitment.

i broke tacks on the upper rear stay and repositioned it.

perhaps I should go this route and get a FIA cert from custom cages uk.

cheers
IG@beechhousegarage

Click to view attachment