NEHA

Have you verified that angle is acceptable? My understanding is that you want the main hoop to be as vertical as possible. Harness bar can be curved to allow the seats to go further back while retaining a more upright stance.

a quick consult with a couple of folks at work, indicate that 10° from vertical is the max according to FIA standards.

I can work with 10°. I was told (unvalidated, I'm sure Sherm can weigh in more meaningfully) that spec Miata maxes at 15° and made a few assumptions there. If I'm limited to 10°, that might mean cutting the rear wheelwells a little and moving the 'feet' back slightly.

On the other hand, there are advantages to being short. I'll have to do some quick math to see how much farther back I can place the seat at 10° - It might be enough to be able to fit, even though that'll greatly limit who else could safely drive this. Time to cut out some of the reinforcement that's in the way, and spend some time doing mockup.

Yep, Art 253 says vertical +/- 10 degrees for the main hoop. NEHA doesnt specify so technically you could get away with more for NEHA. I would suggest trying to follow the 10 degree max since it is possible other sanctioning rules have similar limits and it would be unfortunate if the most elemental part of the cage were rejected elsewhere because of it.

So it's measured relative to 'level' - Doesn't that mean raking the chassis would affect the main hoop angle? That seems like a pretty big loophole.

drummingpariah wrote:I can work with 10°. I was told (unvalidated, I'm sure Sherm can weigh in more meaningfully) that spec Miata maxes at 15° and made a few assumptions there. If I'm limited to 10°, that might mean cutting the rear wheelwells a little and moving the 'feet' back slightly.

On the other hand, there are advantages to being short. I'll have to do some quick math to see how much farther back I can place the seat at 10° - It might be enough to be able to fit, even though that'll greatly limit who else could safely drive this. Time to cut out some of the reinforcement that's in the way, and spend some time doing mockup.

I never much thought about it-so I checked one. It was about 12 degrees.

sdwarf36 wrote: I never much thought about it-so I checked one. It was about 12 degrees.

I figured as much, most of the cages I was looking at for reference on my old Miata had quite a bit of layback to them.

UPDATE TIME!

Because it's Saturday, I have an update on the build! I think I've solidified most of the fender profile at this point. I'd say it looks pretty good, and is ready for some final touches and blending to the bumper.



I don't really have a way to express how much math and thinking went into the cage so far, but here are the key points:

1. It's friction-fit.
I didn't even need to tack it into place, it's so tight against the body.


2. It's symmetrical.
... and level within 5mm from any point to any other point



3. There are no visibility problems.
The diagonal X is 16" lower than the roofline, so it won't interfere with my rear-view mirror.

4. It reclines 10 degrees.
Originally I was planning on 15 degrees, as that would fit the lines of the body and rear quarter windows nicely, but FIA regulations require no more than 10 degrees. I'd like to keep my options open as to what racing I do in this car, so I'm going with the most stringent sanctioning body I know of.



5. I haven't tested fitment with the seat.
I can't really make more space than I am now, and I'd have to remove the remaining horizontal body brace to test fit. I'm just going to put it all off until I have the 'core' of the cage tacked together (main hoop, a pillars, sill bars)

I finally test-fit the A pillars for real, and found that I was dead-on ... on one plane. The other plane didn't go quite so well.



For the second version, I'd like to add another bend just before the A pillars intersect with the main hoop. That would allow most of the A pillar to run right along the window outline, then bend in to meet with the main hoop. Helmet space is at a premium, so I really have to make the most of what I have.

FIA 253-3 shows another bend behind the driver's head, but it looks like it's just a vertical bend. Does anyone see a downside to twisting the tube beforehand, so it bends inboard as well?

The last image you posted... very M.C. Escher-ish as it looks like the bar in the forefront of image is connected to the X.

In other news.... have you panned on location of harness bar. Maybe I missed the answer to this next question... going with FIA seat (no support needed) or SFI (brake to cage needed)?

I'm using Larson's old seat, which is expired so I'll need to add the rear reinforcement to the cage. I'll probably just run the harness bar behind the main hoop, with bends at each end of it. Nothing too fancy there.