Rollbars and Tall People with Big Feet...

[Guest Anonymous]

Guys,

Since I am in the planning phase of my future Z project I am considering some type of rollbar setup. I think it is needed and a great added safety feature. My car will be a street setup with an L6 turbo.

My problem is that I cannot stand the thought of a sidebar in my car. Not even a removable one. Scottie's swing-away is a great idea but I just don't want it.

I value room and usability. I am also 6'3", have wide shoulders and a size 14 wide foot.

I need my room. I want to enjoy my Z when I drive it and have a nice safety margin as well.

I know I can go with a rear only rollbar but is there any design out there that is somewhat unobtrusive up around the driver's seat? Perhaps one that traverses from the rear bar to the front of the car but does it underneath, outside of the passenger compartment?

I am ignorant here so fire away.

 

Craig

 

[This message has been edited by idealz (edited February 08, 2001).]

[pparaska]

I;ve seen people put a kink in the door bar so that it dips down near the hip from shoulder height at the rool hoop. From the kink forward it is at a shallow angle to the front of the rocker box on the inside. You could tie it to the top of a reinforced area of the rocker box up front to keep room for your feet.

 

At the kink, a tube is welded to the bottom of the door bar down to the rear of the rocker box in a reinforced section.

 

This helps stiffen the car (not as much as a straight door bar, but maybe on par with a swing out door bar) but is easier to get over when getting in and out of the car. It adds little to nothing as far as side impact protection. I'm still considering this. I'm the same way - I don't want a door bar as this is a street car. I'd put a full cage in first that went around the door opening.

 

------------------

Pete Paraska - 73 540Z - Marathon Z Project

pparaska@home.com

Pete's V8 Datsun 240Z Pages

[Guest Anonymous]

I was thinking perhaps a 2x3 steel rail running along the floor on the inside next to the door rail. Tie it into the back main hoop and a hoop following the contour of the roof forward and continuing down the windshield post and down to the floor welded to said 2x3 steel rail welded to the floor (I hope you can picture this, cause reading it sounds whack..). Might be a issue not slamming your head on the cage getting in, but after a time or two you'd probably remember it.

 

Lone

[DavyZ]

Craig, I somehow remember having this very conversation about three months ago? The "kinked" sidebar is a very interesting idea; I have seen a Porsche 914 with a "kinked" sidebar and was impressed with the amount of room it afforded the owner to get in and out of the car for daily driving. As has been stated by Pete, if you tie into the loop base from the kinked part with another tube, there should be minimal loss of rigidity. Now, whether this is up to competition spec or not, who knows? I have decided to go with a "swing-out sister" bar, but I'm making mine removable. I will only put it in when in competition (like every nite) driving.

 

Do you know if you are going with S&W or Chassis Works or what? At this juncture, I'm probably going with Chassis Works even though they are more expensive...what am I saying?!? I'll call them and find out which is the best for the money and for what I want to do and then make a decision.

 

David

[Guest Anonymous]

I have talked with others a bit about different methods of doing the sidebar. I almost don't want one. I know that if I go all out for power then it must be done so I need to design in that capability.

I am looking for a little roll protection, a way to stiffen the chassis and a way to beef-up the "crunch capacity" of the passenger compartment. Side impact is always a concern but I drive it now without anything. My car will be street only.

I know the quest for power never ends. My Dad has already talked about a father/son V8 project and we would use a different car. So, my thing is to add something but make it fairly unobtrusive. Is there such a beast?

As far as bars overhead go, I can't have'em. My head is very close to the roof as it is with stock seats!

Davy: I don't remember this conversation personally. Perhaps it was with someone else. Sorry if I missed it and pulled a repeat!

 

Craig

[clint78z]

Just thinking out loud here but when I was doing some frame repair, I noticed that the rocker panel box has a bit of room in it . Mabey you could have the bar run right by the seat tying in front to rear . Might even be able to sneak the carpet right over it with a small bulge .

 

I am double pooched by having a 2+2, I will need a cage and acces to rear seats . I don't care if mines legal, just want some added safety .

[pparaska]

quote:

---

Originally posted by johnc:

I don't think any kind of "low" door bar or a tube in the rocker box will significantly help chassis stiffness. The 240Z chassis flexes like a door hinge in two places:

 

1. Where the front firewall meets the floor pan/trans tunnel. Cracks at the front of the transmission tunnel and where the TC rods are attached to the frame are stress indicators.

 

2. At the rear bulkhead/floor pan. Cracks at the rear of the driveshaft tunnel and at the C pillar body seams are stress indicators.

 

A 4 point welded in roll bar will significantly reduce number 2, especially if you make if a 6 point welded in bar by attaching it to the roof right at the hatch hinges (illegal in ALL sanctioned racing classes).

 

A 6 point welded in roll cage helps with number 1 but to really make the cage work you need an 8 point cage with a knee bar, door bars, firewall reinforcement behind the hood latch striker, longitudinal bars connecting the knee bar to the firewall reinforcements, and addition braces going from the firewall reinforcement to the front strut towers.

 

As stated earlier, low mount door bars and rocker box inserts do very little to help with side impact. So, if they don't add to chassis stiffness or safety, all they are really adding to your car is weight.

 

Sorry for the bad news...

 

---

 

For number 1, I added a 2x3 frame rail from the T/C bracket on new, thicker engine frame rails with lots of gusseting between the engine and floor rail. See my site under "Structural Mods" for pics, etc. I also skip seam welded the tunnel/firewall sheet metal joint and reinforced the firewall where the frame rail comes through.

 

As far as a low bar as I discussed not adding stiffness, I am very surprised to hear this. It makes sense to my mechanical engineer's mind that it would add stiffness and John Washington of Velo Rosa fame uses this technique when chopping the roof of Z's. He also adds a tube along the inner rocker panel to tie to it. John, have you seen this kinked bar added and seen that there was no stiffness gained?

 

It just seems that the long shallow triangle that the forward part of the kinked tube, the short tube from the kink to the rear inner rocker, and the rocker box would add stiffness to the center of the car. BTW, John Washington's kinked bar goes all the way back to the top of the rear strut tower and glances off the inner fender well on it's way down to the kink.

 

Not saying you're wrong, I'm just surprised to hear you say it wouldn't significantly add stiffness.

 

Respectfully,

Pete

[Guest Anonymous]

I'm just gonna sit back and see where this goes!

THIS kind of info is what makes Hybrid so strong!

 

Craig

[Guest Anonymous]

Generally sub frame connectors are just tubing like we're talking about that runs front to back to tie sections together, I can't see how this would'nt help considering the stock frame rails (if they can be called that) are just spot welded sheetmetal channels. IMHO I guess it depends on how much driver space your willing to sacrifice with all the extra triangulation involved in a 12 point cage. I want to be protected as much as the next person, but I don't want to be a gymnist on uneven parallel bars to get out of the car. But I guess its a personal preference, hell I ride motorcycles and there ain't much side protection in that, if a Blazer has your name on it....

 

Lone

[pparaska]

Lone, I don't think subframe connectors are part of the debate here, just kinked (and supported at the kink) door bars.

[Guest Anonymous]

I was thinking part of your structural mod was a frame connector (or what could be called a frame connector) and thats what I was talking about (not to mention I thought the topic went to a 12 point discussion persumably to stiffen the whole chassis), I think I misunderstood your description of the mod (and didn't bother to go over to your site and look...). Ok then, if you'll excuse me while I put on this large pointy hat with dunce on it and find a corner to sit in.

 

Lone

[DavyZ]

Lone: you crack me up, man!

 

Pete: I have to agree with you. The more I thought about what John said, the more it did not make sense. If force is translated from the main hoop forward, then down the side bar, it will continue down toward the "kink," and down from there to the front footwell area AND to the bar going down back to the base of the main hoop. Yes? If it doesn't work in reality, I'm going back to UC Davis and demand a refund!

 

David

[johnc]

I don't think any kind of "low" door bar or a tube in the rocker box will significantly help chassis stiffness. The 240Z chassis flexes like a door hinge in two places:

 

1. Where the front firewall meets the floor pan/trans tunnel. Cracks at the front of the transmission tunnel and where the TC rods are attached to the frame are stress indicators.

 

2. At the rear bulkhead/floor pan. Cracks at the rear of the driveshaft tunnel and at the C pillar body seams are stress indicators.

 

A 4 point welded in roll bar will significantly reduce number 2, especially if you make if a 6 point welded in bar by attaching it to the roof right at the hatch hinges (illegal in ALL sanctioned racing classes).

 

A 6 point welded in roll cage helps with number 1 but to really make the cage work you need an 8 point cage with a knee bar, door bars, firewall reinforcement behind the hood latch striker, longitudinal bars connecting the knee bar to the firewall reinforcements, and addition braces going from the firewall reinforcement to the front strut towers.

 

As stated earlier, low mount door bars and rocker box inserts do very little to help with side impact. So, if they don't add to chassis stiffness or safety, all they are really adding to your car is weight.

 

Sorry for the bad news...

 

 

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John Coffey

johnc@betamotorsports.com

[clint78z]

I am a little new at the whole roll cage setup, so I am no authority on this .

 

However I do know some basics

 

Any cage is better than none, unless it has a bar that can hurt the driver in a crash .

 

The car will be used everday and have people in the back once and a while .

 

Given that the car is unibody, just about

anything will benifit to chassis stiffness .

I think the rocker tube will keep a square car from turning into a rhombus under hard cornering forces .

 

The door bar is nessary to provide a gusset for the main hoop . It will keep the main hoop from delfecting in case of a roll over .

[johnc]

Let's go back to my numbered items...

 

Bad diagram:

 

..................1..........2

Front....__ _|_______| __

...............O............O

 

The Z chassis hinges upward at points 1 and 2 above. You need bracing to keep those hinges from moving and you need to control movement in these areas BEFORE you start worrying about torsional flexing.

 

***

1. Where the front firewall meets the floor pan/trans tunnel. Cracks at the front of the transmission tunnel and where the TC rods are attached to the frame are stress indicators.

***

 

OK, in the original discussions I assumed we were talking about running low door bars to the front hoop of a 6 point cage or tubing in the rocker boxes. In those cases, unless you have something connecting the front of the 6 point hoop to the firewall it really doesn't help with #1 above. Now, the bracing/gussets that Peter mentions DO help connect the front of the cage to the firewall so they obviously reduce that front hinge on the 240Z chassis. Ideally, you would want that bracing higher and you also want something near the center of the car, but that's not part of the context of our discussion.

 

And, I suppose, adding tubing anywhere in a Z chassis will add stiffness somewhere, but the two places I mention are where you NEED to add stiffness!

 

Running tubes in the rocker boxes or subframe connectors under the car are bascially useless unless they connect to the chassis areas beyond points 1 and 2 above.

 

***

2. At the rear bulkhead/floor pan. Cracks at the rear of the driveshaft tunnel and at the C pillar body seams are stress indicators.

***

 

Again, almost any 4 point rollbar helps with this problem.

 

------------------

John Coffey

johnc@betamotorsports.com

 

[This message has been edited by johnc (edited February 09, 2001).]

 

[This message has been edited by johnc (edited February 09, 2001).]

[johnc]

> Won't the front hinge be less likely to

> flex with the rocker box tube connected at

> the bottom of 1

 

Yes, but the more leverage you can get via the door bar (and a resulting connection to and through the firewall) the better. At some point, if the door bar gets too low, there's a diminishing return - where you're just adding weight to the car. Where that point is, I don't know.

 

FYI... in most roll cage construction the primary reason for the door bar is side impact protection. They do add a lot of stiffness but a petty bar is an even better choice.

 

BTW... is this going to be a street driven car? If so, its illegal in most states to drive a roll cage equipped car on the street. Why? Unprotected heads hitting the cage in an accident.

 

 

 

 

------------------

John Coffey

johnc@betamotorsports.com

[clint78z]

Yes it will be street driven car 80% of the time, I will drive it every day of the week (enjoying every second). It is in Canada so I don't think driving with a roll bar will be a problem . Still undecided on how far I want to go with my cage .

[Guest Anonymous]

John,

 

I believe I understand what you are saying regarding the "hinge points" of the Z chassic. The way I understand unibody construction is it is basically three boxes. The first box being the front subframe (engine compartment), the second box being the passenger compartment and the third being the rear subframe. The links between these "boxes" are weak in unibody construction, especially in a Z car that is prone to rust.

 

Now the tricky part, I have installed 2x3 box subframe connectors much like Pete's and have come up with a way to tie the rear subframe into the cage (I am using a 10pt S&W cage), what is the best way to tie the front subframe to the cage? I am considering taking bars from the tops of the front strut towers through the firewall and tie them into the front bars of the cage. The problem that I have is running them through the cowl area. I have seen photos in Bob Waar's book "How to Hotrod and Race your Datsun" and would like to do something much like they did but it appears the bars will have to travel through the cowl area were the windshield wiper mechanism mounts. Is this correct? I have considered taking them lower, under the "wiper mechanism box" but I believe this would cause interference with the engine and would require the "cross bar" to be mounted too low in the interior.

 

Any help with this would be greatly appreciated.

 

Chris

[clint78z]

Good discussion, I hope I didn't come off the wrong way to anybody not my intent . Excellent diagram I know exactly what you are driving at .

 

Won't the front hinge be less likely to flex with the rocker box tube connected at the bottom of 1 . Yes I do agree that it placed in the middle of the door will be way better . But this is unacceptable for my street car, I am 6'1" and 190 lbs . I may be grasping at straws, mabey a 4 point is all that is needed .

[BLKMGK]

Clint - I'm 6 foot 2 and a bit over 200lbs (trying like hell to get lower!). My bar is the usual 4 point in back with bars going forward along the roof line and won to my feet into the footwells. I've also got side bars from about sholder height downwards to I think the front bar or floor.

 

Climbing in and out with Recaro buckets is a bit of a pain but if you've ever looked inside the doors (mine's a 240) you'll see there's not AQUAT for protection! I mean we're talking a tiny piece of sheetmetal ribbing for side impact protection. Remove the guts and tap on it - the door rings like a church bell.

 

Me, I'll suffer the PITA of climbing in and out - the car will be almost all street but not daily driver. I've seen side impact accidents and nearly T-boned someone a few times, I don't want to ever be on the recieving end of that!

 

Now, having said that... My Mustang has an AutoPower bolt in bar. The sides of that bar go right along the rockers and join the roof bar in the footwell. Is that what you all are talking about? If so, it does act much like a subframe connector in preventing twist etc. However from the discussion here it sounds as if the flex point is further forward. It MIGHT give some side impact protection but it would depend on what it was trying to hit you - a telephone pole then yes it would protect. The pointy end of a Buick? I don't think so.... (shrug)