If two asprin are good then 4 are better? I have seen this style of doorbar starting to crop up more and more. We know that "X" bars work in tension and NASCAR bars work in compression and shear mass. So what happens when the two are combined? Is this twice as good? Is this excessive weight? Does this defeat the qualities of both designs?

 

I am no structure engineer, but just on a gut level, I would prefer to see the Nascar bars acnhored at the nodes of the X braces instead of midway down the tubes.

 

I had the exact same gut feeling... and I have a big gut so it knows a thing or two...

I also don't like the bar coming from the a-pillar to the upper Nascar horizontal bar.

Personally, I would have a bigger angle "X" bar with some gussets and get rid of the rest... but I must admit my opinion is uneducated. I am not a structural engineer either!

 

I am a structural engineer, and you are "spot on" (in my opinion). In a severe hit, the nascar bars will push the center of the "X" into the driver.

However, things are not always as they appear. It is possible that this is a real professional build with computer modelling and finite elment analysis behind it. Its definitely safer than my two straight, bolted in door bars.

 

I've only seen this in a few cars and all of them have had both the X brace and the Nascar bars attaching to the front downtube and the main hoop.

 

Nor am I and I thought the same thing. Nothing a cutting torch can't clear up in 2 min. force on the Nascar bars concentrates in the middle of the X bars where they are least able to resist. If you are going to bouble the weight you mighe as well try and double the strenght.

 

Sorry gentlmen. I was thinking more about the soundness of concept mixing the "X" with NASCAR not really about the error of welding the NASCAR bars mid "X" as shown. I wonder at what point the A and B piller just crumble while the mass of NASCAR/X bar and land in the driver's lap? Maybe we want the rolloverhoop to be the strongest part of the cage?

 

I suppose the builder of this car was probably trying to combine the positive attributes of X brace (better stiffness) and the NASCAR bars (better intrusion protection). Even assuming the NASCAR bars are attached to the cage at the right spots, somehow I doubt it's worth the extra weight.

Scott

 

There so much wrong with that I don't know where to start, worst part is they took parts of two completely different approaches and ended up with one that works poorer than either by itself...

 

I recognize that car. The cage was built that way to meet the rules.

Just my opinion - the rules were written with 4 door sedans in mind and it's hard to translate the same thing to something like a corvette.

 

See, now the cage in Kurt's example looks like something you would feel comfortable in doing figure 8 racing.

 

Interesting Kurt. I have never heard of any sanctioning body requiring X and NASCAR bars. I wonder what a FEA would revel about such a design since I don't think there have been any crash tests of that. Your sedan cage is much better looking than the vette cage I posted.

 

I am, and I agree

 

Not light but built with some good solid standard methods used.

The original cage in question. I bet the nascar bars were shaped with the though to fit inside a door more than optimal function. I think they could be improved with some triangulation via tubes opp the points on the X bars. the upper tubes at least look like they could be backed a bit.

Considering the weight of a Vett more in the A pillar and main hoop and perhaps a roof X to cut intrusion might be in order.

 

The pro mx-5 cars have both in their mandatory cage kits.