My car now requires a cage to be able to race legal at the local track. I would like to know the weight difference between the two. Basically I want peoples oppinions on which one over the other, weight comparisions, etc.. I know price wise is a huge chunk of change there for every information I can gather is appreciated. Thanks guys

 

well there two types of mild steel. thers cold press and hot press. the cold is a bit stronger then hot and looks amlost like stainless. but chromoly is a better choise for a roll cage, almost all the BMX bikes use chromoly.

chromoly is also more $

 

i thought certain rules require chromoly?

 

Save yourself and use chromoly. A chromoly cage will weigh less not becuase the material itself is lighter, but because not as much material is needed to obtain the same amount of strength. It also has properties that make it ideal for cage usage.

 

Please tell me what makes chromoly a better choice?(I know) SCCA doesn't allow a difference in chromoly and steel tubing sizes? NHRA does require chromoly for some cars. Doubt yours will be needing that.

 

As far as rules of sanctioning bodies are concerned, I can't help you there, and I'm not saying chromoly isn't the right material for your need either, I just want to share some info that I learned in welding school.

McKinney, which makes chassis for Top Fuel drag racing only uses chromoly in the back half of the chassis of a 7000+ hp race car.

In McKinney's testing, the weakest point has always been where the chromoly is welded to the normal mild steel, and in pull tests it is revealed that improper welding of chromoly can cause under-bead cracking not visible on the outside, only revealing itself when submitted to stress and vibration, such as a drag race car.

I'm not saying chromoly isn't great, it's strength to weight ratio is awesome. But for many racers the additional price of the material doesn't justify the gain in strength when their application will never submit the chromoly to more stress than mild steel could handle in the first place if properly welded and engineered.

Then again, safety has no price, so to some the peace of mind is worth the extra cash.

My sources are an American Welding Society magazine article about McKinney chassis fab and my metallurgy class during my two year welding school.

 

That sums it up pretty good. Not totally but that pretty much hits the meat of the problem. Chromoly by itself is still just steel.

 

in college for our mini baja car we used chromoly; the cages are regulated by strength to have a minimum of 1 in. o.d. 1018 w/0.12 wall thickness, however, we use 4130 that has half the wall thickness and thus half the weight. And to our added benefit its also slightly stronger. So, if you were making a serious racing attempt the cost I think is worth it to reduce the cage weight by half, that is if the sactioning body allows the wall thickness reduction.