Roll Bar Bracing Feedback

[Lonnie-S]

I'm seriously considering leaving off the rear braces on my Hayes Roadster inspired one-off. I'm not convinced they will offer much in the way of safety, but I'd like to preserve the possibility to autocross (not race) it when it's finished.

I'm talking about these guys:

Haynes Rear Roll Bar Braces.jpg

My structure is more developed than the Haynes version as the vertical RHS is triangulated at its base, but it's still made pretty light weight materials. I don't think the braces are an attractive feature and they make dealing with boot access much more complicated. If I decide to include the braces, I need to design/fab/weld the attachment points at this stage.

Roll Bar Brace Structure.jpg

What do you think?

Cheers,

[JAMADOR]

Those angles look mighty 'square' & doesn't seem like they'd offer a ton of actual support in the event the car ended up inverted.

Guessing there's no way to run the support bar to the bottom of where the upward pointed arrow starts? Seems that would give a more triangular & less square angles.

[seattletom]

I'm seriously considering leaving off the rear braces on my Hayes Roadster inspired one-off. I'm not convinced they will offer much in the way of safety, but I'd like to preserve the possibility to autocross (not race) it when it's finished.

Lonnie, instead of rear facing braces could you add provision for a removeable forward facing brace to use for track events? Perhaps going from the roll hoop to the lower rail on the passenger's side.

[ZiG]

If you do want to autocross it, you will need some kind of brace.

From the SCCA SOLO rules Appendix C (Roll bar standards):

"D. Bracing
1. It is recommended that braces be of the same size tubing as used for the
roll bar itself.
2. All roll bars must be braced in a manner to prevent movement in a fore-
and-aft direction with the brace attached within the top one-third of the
roll hoop, and at an angle of at least thirty degrees (30°) from vertical.
It is strongly recommended that two such braces be used, parallel to the
2024 SCCA® National Solo® Rules— 277
Appendix C - Roll BaRs
sides of the car, and placed at the outer extremities of the roll bar hoop.
Such braces should extend to the rear whenever possible.
3. It is suggested that roll bars include a transverse brace from the bottom
of the hoop on one side to the top of the hoop on the other side."


https://cdn.connectsites.net/user_files ... 1704906773

[Lonnie-S]

@JAMADOR
My thoughts exactly. The braces might look impressive, but not really much in the way of safety.

@seattletom
Nice idea, Tom

@ZiG
I was afraid of that. Maybe I can marry the SCCA Regs with Tom's idea - Removable rearward braces?

Cheers,

[KB58]

A removable forward brace would be much better, especially placing it as diagonal as possible.

[BostonWill]

My rear roll bar supports go to the lower rear corners. More difficult to work around for the tank & a future cover. But I think they are strong.

IMG_0568.JPG

[JAMADOR]

Will's setup is what I was directing toward, but a bit inboard to meet the join of the 2 tubes in Lonnie's photo.
Looks much stronger than the trapezoidal arrangement of mounting it to the top hoop.

[tibimakai]

I won't be adding those either, but I won't be racing.

[Bent Wrench]

In my eyes those braces are pointless as there is little strength.
I think if you turn the car upside down and dropped it the roll bar would punch right through the chassis!

[Driven5]

I don't think it's ideal as-is, but I think it's still better than not having any roll hoop bracing. The main concern is mousetrapping on the driver. The joint would act more like a (mid span side supported) curved tube, such that it would be significantly weaker against buckling in compression, but would still greatly limit the main hoop from collapsing forward (toward the occupants) under tension.

For me, it just needs an extra support to triangulate that node. However, I also wouldn't want to make it 'too stiff' in a rear hit, such that it could transfer enough load to deform the cockpit rather than the boot. So while my first thought was running a tube from the main node (roll bar base and coilover mount) back, I think one run up from the bottom area might be a better approach without compromising 'too much' on the boot.

[RTz]

Lonnie, that's roughly what I did to buttress my stays.

[Lonnie-S]

@seattletom
@KB58
I took a look at a removable diagonal into the passenger side. Structurally, you two may be right. However, at this late point in the game I'd have to change other things to make it work. I'm too lazy to do all that for something I can't keep as a permanent part of the setup.


@BostonWill
@JAMADOR
Like the passenger side diagonal, it's too late in the game for those significant changes.


@Bent Wrench
Well, I'm slightly more optimistic than you. I think it would just bend the crap out of everything back there: top hoop; lower hoop; verticals; and triangulation. But if things moved even 8 inches say, I think the safety provided would be very minimal.

@Driven5
@RTz
I may be able to make a version of what you two are suggesting work. I've got to put the fuel tank and battery tray back in place to see if it will fit, but it might just work. If I made the two back braces removable that would look like good solution to me. I'd put the braces on for autocross and leave them off (I think) for street use.

Thanks for all the suggestions, gents.