Roll bar angle:

[RidgeRunner]

Well you could just locate the vertical forward more. The uprights can be positioned in any location along the top frame rail. It doesn't matter whether the upright is vertical or leaned back. I agree with you John, the load is spread over a greater distance. But it can be accomplished with either style.

Doesn't take too far forward for the front vertical hoop to start interferring with the bailout.  Everything has an effect on something else, compromises, compromises.

                               Ed

[maguromic]

We are designing our cage structure on the roadster now, and this is a sketch our team engineer Steve came up with to help visualize it.  Our forward hoop angle (37 degrees) is determined by the 3” clearance helmet rule and the appropriate floor intersection with dash hoop structure.  But if a possible future rule is going to say at least 30 degrees, then we have to re evaluate how everything is going to work all over.  Looks like before we do anymore we need to send this off to Lee and the gang to get their approval or disapproval.  I hope these rule recommendations are made from engineering evaluations and not from a knee jerk reaction or what someone thinks might work or might not work. Tony

[RidgeRunner]

Nathan,

     Big public thank you for your pro active involvement in getting this issue clarified.  It's a big help for all of us scattered around the country [as well as for the inspectors] to being as ready as possible for that first big inspection on the salt.

     Email sent regarding another build I am involved with.

                                Ed Purinton

[saltfever]

Hey guys I appreciate all responses. I agree that a 30 degree lay-back looks pretty and may be aerodynamic. But pretty doesn't cut it! If SCTA wants a 30^o lay-back it has to be for strength and safety. I am not an engineer . . but do I have to be? Sit an 80,000 lb load 3" above your head and tell me which geometry is stronger. (vertical or 30^o lay-back) An open class tractor can weigh 10,000 lbs. They build for strength, not "pretty".  

Edit: Sorry I posted this without seeing the two latest posts coming in.
Ridgerunner: I agree that egress is very important and it may be a consideration with lay-back angle. But as Tony says, we need to know what factors were considered when justifying such a change. Especially, if something was considered more important than strength. I'm not saying ultimate strength stands alone . . . but what is the hazard that preempts it?

[jdincau]

Why not contact Steve Davies <flyingkiwi97@aol.com> directly with your questions?
Jim

[Gwillard]

Hey guys I appreciate all responses. I agree that a 30 degree lay-back looks pretty and may be aerodynamic. But pretty doesn't cut it! If SCTA wants a 30^o lay-back it has to be for strength and safety. I am not an engineer . . but do I have to be? Sit an 80,000 lb load 3" above your head and tell me which geometry is stronger. (vertical or 30^o lay-back) An open class tractor can weigh 10,000 lbs. They build for strength, not "pretty".  

Edit: Sorry I posted this without seeing the two latest posts coming in.
Ridgerunner: I agree that egress is very important and it may be a consideration with lay-back angle. But as Tony says, we need to know what factors were considered when justifying such a change. Especially, if something was considered more important than strength. I'm not saying ultimate strength stands alone . . . but what is the hazard that preempts it?

Given the same tube size, base dimensions, height, etc. with the ONLY difference being the front hoop being layed back vs. straight up....put me under the one that is layed back. Basic rule of thumb for virtually all structures is that arches and triangles are far stronger than squares and rectangles.

[saltfever]

 
Given the same tube size, base dimensions, height, etc. with the ONLY difference being the front hoop being layed back vs. straight up....put me under the one that is layed back. Basic rule of thumb for virtually all structures is that arches and triangles are far stronger than squares and rectangles.

Agree. But the vertical is not standing alone by itself. It would also be triangulated.

[desotoman]

Saltfever,

I don't know how long you have been around SCTA and LSR but SCTA has to require safety for two types of surfaces. Salt and Dirt. Very different surfaces, so they have to have vehicle roll-cages designed for the surface which will cause the most damage, which in my opinion is the dirt.

Many years ago I was at El Mirage and witnessed a fatal Lakester accident. As I recall the motor blew up and a rod took the starter out. The rear tire rolled over the starter around 200 mph. The car instantly went upside down and when it hit the cage DUG into the dirt, ripping the cage right off the car. Needless to say the driver did not live to race again.

As a result of this accident the SCTA mandated plates be welded from the main frame to the roll cage. (Gussets) page 25 of the current rule book. This is just one example of Roll Cages being a work in progress.

Most of the rules are made to protect us from ourselves, so that we can comeback and race another day.

Tom G.

[saltfever]

Why not contact Steve Davies <flyingkiwi97@aol.com> directly with your questions?
Jim

Jim, thank you. I didn't see his contact info in the rule book but should have checked the SCTA web site. I needed to contact him about another issue and just left a message.

[Gwillard]

 
Given the same tube size, base dimensions, height, etc. with the ONLY difference being the front hoop being layed back vs. straight up....put me under the one that is layed back. Basic rule of thumb for virtually all structures is that arches and triangles are far stronger than squares and rectangles.

Agree. But the vertical is not standing alone by itself. It would also be triangulated.

As I said, all else being equal. Add the same braces to the layed back version and it's strength would again exceed the vertical version. If enough bracing were added either structure would be strong enough to support any load you want and the discussion becomes moot.

[saltfever]

Saltfever, edit . . . I don't know how long you have been around . . . .
The car instantly went upside down and when it hit the cage DUG into the dirt, ripping the cage right off the car. As a result of this accident the SCTA mandated plates be welded from the main frame to the roll cage . . . This is just one example of Roll Cages being a work in progress. Tom G.

Been around a long time but as you know very few ever get close to an accident and even less see any analysis. Many thanks for your post and zeroing in on a critical factor. Read my post #17. I can see "digging-in" is a very important consideration but so far I, nor anyone else, could point to real data. It only took 3 pages to get you to speak up . . . don't wait so long       

[saltfever]

As I said, all else being equal. Add the same braces to the layed back version and it's strength would again exceed the vertical version. If enough bracing were added either structure would be strong enough to support any load you want and the discussion becomes moot.

Opps, you did say . . .  "all things being equal" . . .  but the discussion is not about strength.  But why is a 30^o angle better than 90^oangle. If it is not a strength issue as you indicate, then it must be something else. Tom most likely has the answer.

[hotschue]

Hello all...Speaking from a user point of view, I had a cage built by Dave Urehara, more than a few years ago.  The cage was 30 degree +- took a frontal hit then ground 1/2 the diameter of the top of the cage before it stopped (200+ on asphalt).  Definitely saved my bacon I walked away.  I am currently building a car in the "build diaries" and my cage is identical to the one I ran in my f/c.  Pics are posted, haven't built the substucture, cage is tacked to upper hoop.  A properly constructed cage, properly welded is the answer.  Thank you Dave I'm sure he's watching.....

[John Burk]

Another important part of the design is whether the hoops continue to the lower rails . In Tony's sketch his appear to be that way . To me that's the strongest design . I made mine that way and have 1 1/4" tube gussets fore and aft where the upper rails meet the hoops . It's barely visible in this photo .

http://www.motorsportsinnovations.com/Bvile-pics/streamliner%204-02%20a.jpg

[hotschue]

John, If you look at my build I haven't done that vertical tube.  I wanted to do some research on what was stronger.  When "SEMA Approved" regulations came into being it required the vertical tube to be offset to the rear approx. 4" had something to do with controlling the shock to the lower rail.  Since I'm not an engineer, I was going to look into it before I commit to a design.  Anyone out there with more infor would be appreciated.