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I don't know what manufacturer you're speaking of, but I'd imagine that they say that for liability reasons.  If they say it will for sure hold the car up, and something goes wrong, guess who gets included in the law suit.  Oh , who am I kiddin, they'd get sued anyway with the frivolous law suits the way they are.

In all reality, it doesn't take much to hold the car up.  It really doesn't weigh very much.  That size hoop in A36 steel is probably capable of holding  the 1000 to 1500lbs required of it in that event.  The problem could lie in a multiple rollover where the hoop coul dbe torn free from its mount.  It wouldn't hold anything up then.  Anybody here have an A36 Head?  

Oh, hijack away!  No problem with me.  It all ties in to the handling anyway.  I did enjoy the Adams book, but it has been a few years sisnce I read it.  I need to get it out again and go through it.

I believe you are right about the differing styles though.  These cars are most often designed for non-sway bar stiffness.

Great conversation though!

LMH

As far as losing traction before the frame will flex goes, it will depend on the steepness of the curve and probably some other factors as well.  What it boils down to is how much force is applied to a corner of the vehicle and at what angle.  The force breaks down into a vertical and horizontal component.  The horizontal will want to push the car sideways possibly breaking traction while the vertical will push down on the corner actually adding to the friction resisitance making it less likely that the tire will break loose.  The down force on that corner also has an equal and opposite up force at the opposite corner.  This it what causes the frame to flex.

You are absolutly correct that adding a cage ends any need for a backbone as well.  The cage will stiffen the chassis much more than a backbone will.  I'm not looking for an all out competition racer, but something that is a great street car that will also perform well on the track days I'd like to attend every now and again.

Thanks!

A friend of mine who used to manufacture kits schooled me on some of the things to look for in a car with a ladder frame to determine how much flex there is.  He maintained that a good indicator is to put your finger in the joint between the door and the body while doing some hard cornering.  If the chassis does have any significant flex, that gap will open and close depending on the forces.  He said that on some kits he's been in there is enough flex in that gap to pinch your finger!

Don't get me wrong on my abilities.  I am not a chassis/frame designer.  I design building structures by trade.  When it comes to geometry/roll center, and that type of thing, I really only know what I've read in the Chassis Engineering  book by Herb Adams.  It is actually a really good book.  The structural abilities of the frame are basically the same as any structure though.  Loads are loads as well.  The only difference is what is making the loads and where they are being applied.  I guess what I'm saying is that I'm not an expert on chassis design.

Thanks for the input guys, this has been a great topic with some excellent input.  Oh, by the way, great to see another Jayhawker!!

Sorry!

I'm not here to blow anybody out of the water!  I'm certainly not looking to put down the Hurricane car, as I think the chassis and body both look well designed and thought out.  Thanks for the info.  Looking at some of the build pictures I have seen, it looks as if the steel between the driver compartment and the engine compartment is a bolt in item.  Is this correct?  If so, I think it might be problematic to add the backbone.  Also, I was thinking more along the lines of fitting a tube frame underneath the tunnel, and leaving it intact.  If I was to cut out a section of the fiberglass shell that large, it might not want to hold together too well.  I have to admit, I'm fairly new to the Hurricane, so I don't know how it is all put together.  Do you think there is enough room under the fiberglass tunnel to fit a steel tube frame, or would there be no room left for the driveline?

Thanks for the help!!

My question was not simply based on the FFR or other manufacturer claims that a backbone is stronger.  I am a structural engineer and have a pretty good understanding of the science behind strengths.  The basic concept is that a section, be it a steel beam or a car frame, gains its strength from the vertical dimension of its section.  The section modulus determines the strength of the section and the major factor of the section modulus is the vertical component.  That is why most steel beams are of the "I" variety with very little steel in the cross section.  A small amount of steel, but laid in a vertical section resists bending quite well.

I understand that when your car is on the lift, but only partially supported that no deflection is noticeable.  When the car is under power though, and tearing through a corner at 20-30mph or more, the forces are not only that of gravity.  The forces are multiplied several times due to many factors including speed, front/rear weight ratio and others.  In other words, while the frame may only be deflecting a quarter of an inch when hanging from a lift, it could be 3/4 to an inch when cornereing depending on the actual forces involved.

Adding a backbone to the chassis gives it that vertical component that will resist bending much more.  The stiffness in action is what i'm concerned with.

I do like the looks and the kit components of this Hurricane car.  I'm not sure how soon I'll be buying, but it will probably be within the next 8 months to a year.  I just want to know if this is a possibility for the chassis.  I'm not tryong to start any brand wars!

Sorry about the technical diatribe as well.  If any of you guys know or are engineers, then you know we like to talk about this stuff!

How difficult would it be to add a backbone to the Hurricane ladder frame.  One of the things that is important to me in a chassis is torsional rigidity.  I want a chassis that resists twisting around hard corners.  This helps reduce large amounts of stress in the fiberglass body.

Looking at the pictures, it looks as if a backbone could be fabricated underneath the tunnel.  Does anyone who has built one see a reason why a backbone could not be fabricated there?

Anyone think that Hurricane might be willing to add one during the chassis build?

Thanks!!