Chris Alston Roll Cage

[DavyZ]

Lone, I'll be happy to verbally slap you, but then again, I really like you and I don't want to appear rude...instead I'd like to say that I think your rollbar tubing looks pretty darn good and I'm sure you'll have it all welded in pretty soon. Are you going to have any clevis joints put in the diagonals or any such thing? Just wondering.

 

Keep up the good work--the car is looking better and better. It was good seeing both you and the car at the Rio Vista meet.

 

Cheers,

 

Davy

[katman]

I didn't initially criticize anything, that would depend on what application the cage is intended for, and that was my question. If you don't expect anything out of that cage then I have no criticism. But since you asked, here are two reasons why it is unsafe, for racing anyway.

 

First, the main hoop for the chassisworks designs (and I think the S&W too) are missing an uninterrupted diagonal in the plane of the main hoop from a point above the driver's right ear to the bottom of the passenger side of the hoop, which effectively forms a truss above the driver's head. To not have this, which is so elementary from a structural standpoint (and required by SCCA), shows a lack of understanding of basic roll cage design principles. Sorry, their diagonal that goes from the hoop to the strut tower is worthless.

 

Second, the chassisworks designs have a horizontal bar at dash level for the forward section of the cage. When you are T-bone'd, if the door bar doesn't collapse (and their single bar will, I assure you) the floor at your ankles will. This is because the floor of a Z will not resist the sideload imposed on the forward downtube by the door bar with most of the load taken by a single side of the floor. To fix this, the horizontal bar needs to be closer to the door bar intersection, passing right above the tranny tunnel, to help get the sideload over to the other bar (with their high bar the forward downtube just bends when the floor collapses) and react the load with both sides of the floor. Better yet is to add tube from the downtube to the firewall just above the dead pedal.

 

The chassisworks units use 1-5/8 diameter 0.134 wall tube. A real engineer would have used 1-3/4 diameter 0.095 wall tube for the same bending sitffness (axial stiffness is plenty in either case) at 27% less weight. And since all the weight is above the CG you want it to be as little as possible.

 

There's more, but that should be enough.

 

Now if you want a dissertation on roll cage design for a 240/260/280Z, somebody dig up that old article in the defunct Z-Car Mag on building an ITS 240Z, the issue that discussed the cage, and post it out here we we can all read it. I would be happy to but I don't know computers. It discusses the load paths involved and where/how to get the cage loads into a flimsy Z unibody. Very thorough and explains "why".

[stony]

MAN!!!! if i could get just the main hoop and halo id be set i can get the rest of teh stuff locally in alaska to finish it

[Guest the_dj]

I have a serious question. How much would it cost to tube frame the car from bumper to bumper? Also, how long would it take? Any estimates?

 

If I was to ever put a cage in my car, one thing I would want to be sure of is that it was done right...as in a full tube frame.

 

DJSS