The 24 Hours of Lemons Forums → Lemons Tech → Accepted front-hoop configurations for roll cages
I guess it's been too long since I caged a full frame car....I recall my '74 Parisienne had plenty of meat in the frame...
Our builder did not notch the frame to weld it in he actually used a holesaw and bent the tube to drop through the holes in the frame, then he welded the tubing to the top and bottom portion of the frame so it had 2 nice solid points of attachment. Just remember that when you are closing up the gaps to leave a space for the tech inspectors to verify the welds are 360Degrees around the tubing. This was done on a 97 crown vic at 6 points where the cage attached to the frame. Pics here http://pantingpolarbearracing.com/techstuff.html there is a pic of the weld to the frame.
Finally, you must have one main-hoop diagonal support--the simplest way to accomplish this is to run a clean, straight tube from the driver's-side top corner of the main hoop to the passenger's side bottom cage-mounting pad at a more-or-less 45-degree angle. This bar will likely intersect your harness bar; you can make either the diagonal or the harness bar from two pieces to deal with that intersection, but the finished two-piece section must still form a very straight, very clean line.
I pulled this from the Lemons website under rules, my question is my 2 piece diagonal bar legal? from the sounds of this discussion it wouldn't be. please let me know thanks Steve
. This bar will likely intersect your harness bar; you can make either the diagonal or the harness bar from two pieces to deal with that intersection, but the finished two-piece section must still form a very straight, very clean line.
Steve
Sounds pretty cut and dry to me. Unless your diagonal bar is all out of line you should be fine with a two piece.
Diagonal one piece is what is preferred and just do one piece. Then harness in two pieces
My deal is I'm running out of time the race is in 2 weeks so I would have to cut out the bars in the back out of the car and refab some new ones, If it will pass I need to weld the roof back on so I can finish the car, I'am thinking of adding some gussetts to help it out also.
Due to confusion over the use of the word "continuous" in describing certain parts of the cage, we've updated the rules to say this:
Each major load-bearing member must be formed from its own single, continuous tube.
Basically, we're trying to avoid welded-together sections in major stress-bearing parts of the cage. ALL of the following designs are legal front-hoop configurations; welding the bolted sections (where applicable) is highly recommended:
NOTE: These illustrations serve to illustrate different styles of front hoops. Other elements of the cage designs shown may not conform to the Lemons rules. http://www.24hoursoflemons.com/pricesandrules.aspx
Single-piece front hoop:
http://www.hoverd.org/Tim/Fury/images/r … ign_01.gifLeft and Right bars:
http://speed-eng.com/store/images/Roll%20Cage.jpgHalo loop:
http://www.therangerstation.com/tech_li … awing1.gif
Nick I don't read where Chrome Moly is allowed. As you know Chrome Moly is much stronger but slightly smaller in diameter and thickness.
Would Chrome Moly be allowed?
Assuming good tig welds, bends, and design?
Nick I don't read where Chrome Moly is allowed. As you know Chrome Moly is much stronger but slightly smaller in diameter and thickness.
Would Chrome Moly be allowed?
Assuming good tig welds, bends, and design?
Insurance requires a MINIMUM diamiter and thichness. You have to use those sizes. You have an option of material, but you must stay in that size.
RobL wrote:There is nothing to stop a crushing force on the main hoop (as in a rollover) since the rear stays would bend.
The engineer in me disagrees strongly here, there is plenty to prevent a serious crushing failure BUT...
Even with an extremely large load the x bars would prevent a complete folding of the cage structure. Yes it is quite probable that there would be local bending near the top of the structure BUT unless the welds failed completely the cage would absorb MORE energy in bending than a 'Lemons legal' cage. That said, you are relying on the quality of the welds to hold in shear on a serious vertical / diagonal impact at the top of the main hoop to prevent a failure and compression of the cage.
Designing a textbook rigid structure is easy. That is the point of the rules, build a rigid structure out of solid materials known to be strong enough to prevent serious injury in typical collisions.
Engineering a structure to give in a controlled manner and minimize the loading on the occupants while providing safety in a very high energy impact is far more difficult and MUCH harder to verify. This is why the rules are fairly strict for cages. Yes, you can make the argument that a well engineered cage with intentional impact absorption zones is better but unless you have a certified engineer willing to sign his professional credentials against it you should build to the rules.
I am always tempted to 'improve' on the rules but then I think like a liability lawyer / professional witness and decide to just build what is mandated to avoid the hassle.
The mandated structure is pretty damn good. Use solid gear and a head/neck restraint and be done with it.
I too want to improve on the rules but if the cage does not extend out past the passenger compartment the front and rear of the car can still act as a crush zone.. The side impact is a concern but the only real solution is to move the driver closer to the center of the car and find that NASCAR mandated foam between the door skin and the side impact bars..
NASCAR found a really significant reduction in G loading on side impact with that stuff..
I haven't shopped for it yet but I'm afraid it's wicked expensive.. Might tempt me to use regular High density foam and simply wrap it in aluminum for fire protection..
Don't know how the club will react to that.. They sure got upset when I wanted to use some Chrome Moly I had. (It's off by a tiny bit something like .093 thick and 1.72 in diameter. You'd swear they thought I wanted to steal their children the way they came after me)..
The best way for clarification is to email nick directly at nick@24hoursoflemons.com
I don't know how often he checks on these threads.
The 24 Hours of Lemons Forums → Lemons Tech → Accepted front-hoop configurations for roll cages
