Rollcages, again. 4 point + subframe connectors

[Guest macks]

I've spend half the day reading all I can about rollcages in zeds, a lot of which isn't applicable to me because the maximum allowable street registerable cage is a 4-point, as per local regulation. Hopefully with this thread we won't go over too much stuff that's already been extensively covered. In combination with subframe connectors, I'm hoping to put ~380lbft through the car, running R-compound tires and 175front/225rear springs, with stock swaybars in a 260Z 2-seater. Primarily a weekend auto-x and track car - nothing overly competitive - with enough street use to justify it's space in the driveway.

 

I'm worried that it won't be enough to stop paint cracks - opinions?

 

So, rather than go all-out and do everything I can under regulations, I'd like to minimise the weight penalty of chassis reinforcement. I'm questioning whether the rearward connections from the hoop to the rear strut towers are really necessary. Given the lack of a 'b' pillar, I can see the benefits in using the hoop to attach to the top corners of the roof and with the side panels in a kind of psuedo b-pillar manner, but I can't see the benefit of the rearward bars given that the C pillars are already substantial and run parallel to where the bars would be. What do you guys think?

 

Likewise for the doors. As others have suggested, being in a low light car in the age of SUV's makes me more than a little worried. Legally, I can't put a bar across the door opening unless it's removeable and used 'off-road' only. What they can't see they can't object to, so the inside of the doors and the underside of the floorpan are fair game. I'm toying with the idea of a short second frame rail under the area of the door cavity, but haven't really thought it out. While I'm going to reinforce suspension mounting points, my car is pretty rust free and I like my frame rails - I would prefer not to cut them out and replace with SHS and U-shape steel.

 

So, after all that:

- are the rearward supports from a roll hoop to the strut towers really worth the weight vs just a roll hoop?

- what can I do to the inside of the door to substitute for a door bar, while still having full use of the window?

- what can I do to the underside of the floor, short of the famous pete paraska style re-frame, to help stiffen/safen the car?

- is there anything else I can do?

 

Cheers! 8)

[johnc]

> - are the rearward supports from a roll hoop to the strut

> towers really worth the weight vs just a roll hoop?

 

Absolutely!

 

> - what can I do to the inside of the door to substitute for a

> door bar, while still having full use of the window?

 

Nothing, you'll also have to reinforce the door jambs, door latch and striker, etc. to make a door bar effective.

 

> - what can I do to the underside of the floor, short of the

> famous pete paraska style re-frame, to help

> stiffen/safen the car?

 

Not much, you'll have to run a subframe from about where the TC rod mounts all the way back to at least the underside of the rear bulkhead to have something effective.

 

> - is there anything else I can do?

 

Triangulate the front strut towers, side to side and back to the center of the firewall. Weld tabs onto your roll bar and connect it to the roof where the hatch hinges are and connect it to the little knobs in the body under the rear 1/4 windows.

[Guest macks]

Cheers for that

 

> - are the rearward supports from a roll hoop to the strut

> towers really worth the weight vs just a roll hoop?

 

Absolutely!

 

How? What loading do they see?

 

A lateral rear strut bar I can understand, but bars parallel to substantial existing metal doesn't make such obvious sense. Unless they're a failsafe to hold the rollhoop up...

 

I also don't believe the rollhoop is allowed a diagonal, but I'll have to look into that - it seems a little ill-considered.

[SleeperZ]

Cheers for that

 

> - are the rearward supports from a roll hoop to the strut

> towers really worth the weight vs just a roll hoop?

 

Absolutely!

 

How? What loading do they see?

 

A lateral rear strut bar I can understand' date=' but bars parallel to substantial existing metal doesn't make such obvious sense. Unless they're a failsafe to hold the rollhoop up...

 

I also don't believe the rollhoop is allowed a diagonal, but I'll have to look into that - it seems a little ill-considered.[/quote']

 

I can't directly answer the loading question, but just to hold the hoop up is reason enough for me. Also seems strange the roll hoop wouldn't be allowed a diagonal - that's also a "failsafe" for a side roll, keeping the hoop from collapsing.

[ZROSSA]

Macks,

 

Have a talk to some of the local rally guys. There cars have to be used on public road between stages. Some of these cars have pretty impresive cages. You could also use the trans tunnel as a structural member. Do the strut triangulation like John said and then run tube from the inside of the fire wall along the trans tunnel and then back up to a rear strut brace. Kind of like a TVR chassis, or maybe the center section of a lotus 7 type trans tunnel. Not the stiffest structure known to man but can it can be hiden under carpets and things and should go a long way to stoping the chassis flex. I really think this is a better solutin then the beams underneath. You could use really light tube and triangulate it the whole way along. Lots of fun with the welder.

 

Douglas

[johnc]

> How? What loading do they see?

 

The 240Z chassis flexes up and down like a hinge at the base of the firewall and at the base of the bulkhead behind the seats. The C-pillars often crack at the welded joint about halfway up their length from the rear flexing. By mounting the roll bar main hoop on the floor pan as close to the rear bulkhead as possible and then bracing it to the top of the strut towers you effectively eliminate that flexing.

[Guest macks]

Cheers guys

 

SleeperZ-

I'll look into it - it does seem a little silly that they wouldn't allow it.

 

ZROSSA-

The whole cage legality thing has me confused. I have in my hand the official RTA street legal cage booklet, and they're very specific about 4-point being the absolute maximum allowable. Yet - Cuong, the chap with the yellow zed and a single turbo RB26 - lives in Perth and has a very elaborate cage in a street registered vehicle. I have no idea how. I've also talked to every car owner I've seen with a full cage in their street car and asked how it's possible, and they all seem to suggest it might not be completely legal but it was approved ages ago, or that the RTA doesn't know about it and they haven't had a problem with the cops. Yet, I'd hate to have a crash and have my insurance invalidated because the car isn't street legal - unfortunately, a very real risk. With rally cars specifically, They have a termporary permit setup, either for the duration of competition or for very limited street use. Either way, the drivers must be registered with CAMS and have competed in x amount of motorsport at y level to qualify for the special temp permits.

 

But I don't know how Cuong's car is legal. I want to talk to him about that one...

 

johnc-

Thanks. That's just the answer I was looking for.

Short of door bars and a full cage extending through the firewall to the front strut mounts - what can be done about the flex about the firewall? Pete's sub frame connectors are looking a better prospect at this point...

[johnc]

Triangulating the front strut towers to the top of the firewall mostly solves that problem. The firewall itself doesn't flex, the sheet metal structures forward of the firewall do.