Project Professional Awesome Time Attack Evo: Part 1 – Roll Cage and Chassis in Detail


It ended up being higher than initially anticipated. Blame my freakishly long torso.
The front strut towers were reinforced due to expected increases of load from the aero and higher cornering speeds. This ended up being very elegantly done so as to meet the cage precisely.
You can never be too safe. It would suck if the wrong bars were in the wrong place.

As mentioned before, I’m not an engineer, but it’s good to know some basics about the materials you’re working with. There are generally two types of tubing recommended for use in cage design and we feel in most situations, only one is practical for use in a unibody car. The two materials are chromoly and DOM (drawn over mandrel) mild steel. We use the DOM material in our cage design. Why? Chromoly is the go to choice for a lot of cage builders because it’s stronger than DOM at the same tube size. Some sanctioning bodies allow for the use of smaller tubing with cages built from chromoly, thus a chance to save weight. Unfortunately, like most cool things in life, there are drawbacks. Chromoly is more brittle than DOM mild steel and when it fails, it can fold rather than bend. Also, it is more sensitive to heat, so where joints are welded, the chance of failure increases unless the joints are normalized. What is normalization? Normalization is where hardenable steel is heated above its upper critical temperature (north of 1300 degrees F in this case) and allowed to air cool to improve its ductility and toughness properties. Some builders just torch the joints and call it good, but doing it properly would actually call for baking the whole car. Not very realistic and the unibody probably wouldn’t handle it regardless. DOM cages don’t have these particular drawbacks.


On the left is a prime example of a T-junction/dead node. The front bars intersect the A-pillar bars at a 90 degree angle. In a front end collision this can cause the A-pillar bars to collapse. Adding an additional cross bar at the door, such as on the right, would greatly improve strength.
…and here's an example of having too many bends in a bar. In a roll over or side impact, these bars would likely fail at each unsupported bend.

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