The purpose of roll bars and cages is to add structure to your car allowing more protection to the driver in the unfortunate event of a roll-over. It also stiffens the chassis, which is the framework plus the guts, including your engine, transmission, braking system, etc... . For cars up to 3500 pounds, the most common material used for roll bars or roll cages is DOM mild steel, or Drawn Over Mandrel. Finding roll cages or roll bars made of DOM steel can range anywhere from $80- $2500.
Another option for your roll bars or cages is Chromoly or Chrome-Moly. Although more expensive than the most common DOM steel tubing, it is more light-weight, allowing your car to travel more quickly. Thus, being the most common choice in drag racing. Both Chromoly and DOM tubing meet race standards and are able to be MIG and TIG welded. When welded properly both methods are equally strong.
Now let’s get to the difference between roll cages and roll bars. Roll bars are a basic 4-point system. This includes a main hoop, harness bar, and at least two rear bars. They are good for dual purpose track day cars and mandatory when racing convertible cars. Roll cages are a 6-point system including pillar bars, a windshield bar, roof bar, door bar, dash bar, harness bar, and two rear bars. Both included a diagonal bar for lateral support. You can add more points to your system, although some race classes do not allow them. All bars and cages should fit tightly to the interior of the car touching slightly at all joints.Before purchasing or building your own roll bars or cages you want to look at your rule book. Different types of races have different rules and requirements. For instance drag racing does not have the same rules as rally racing. It is very important to know what is and is not allowed before hitting the track!