First and foremost roll bars and roll cages are designed to help protect the vehicle occupants from injury in the event an accident. This is the first line of defense. The roll bar/cage design is generally determined and limited by the rules that govern the vehicle class. The SECONDARY function is chassis rigidity. Never sacrifice your safety for the sake of rigidity.
Roll Bars typically have 4 points. This simply means the bar attaches to the chassis at 4 structural points. They consist of a main hoop, harness bar and at least two rear bars. Most have a diagonal bar within the main hoop to offer lateral support in the event of a roll over. Roll bars are a good option for the dual purpose track day car and are mandatory when tracking any convertible.
Roll cages typically feature 6+ points. A roll cage includes, but is not limited to, A pillar bars, windshield bar, roof bar, door bars, dash bar in addition to the roll bar listed above. This is the most common style cage for a race car. To be sure that you're building the proper cage, always consult the sanctioning bodies rule book and the builder. Pending the rules, roll cages can include extra points that anchor the cage to the chassis. Sheet metal and tubular gussets that anchor the cage to the chassis are examples of extra points. Additional gussets are recommended when possible, however most classes don't allow them.
When selecting a roll bar or roll cage, determine what kind of racing you plan to participate in and be realistic. After you have selected what type of auto sport you’ll be participating in, consult the rule book for that sanctioning body and class for what type of cage/roll bar is required. The class rules will dictate how many points and what designs are allowed.
Watch for yourself. This is the second EVO chassis Piper Motorsport built for this customer. After a left front tire failure the driver loses control and shoots off the track. The initial impact into the barrier was recorded at 86 mph. The car flips violently and cartwheels until until it comes to a stop on all 4's. This was a brutal crash. Thankfully our client was unharmed and was able to exit the vehicle without issue as you can see from the video. He only suffered minor bruising from the impact. Again, we are very thankful he was able to walk away. We stress, do not take safety lightly. These are great reminders that though racing is fun, it can also be deadly. It happens fast and unexpectedly. Prepare for the worst!
*WARNING - STRONG LANGUAGE*
The two most common materials used are DOM mild steel and chromoly. DOM (drawn over mandrel) mild steel is most popular due to it's price and ability to be MIG or TIG welded. Chromoly is a popular choice among drag racers or those who are fighting to save every ounce of weight as possible. Because of chromolys higher tensile strength, most rules allow you to use tubing with a thinner wall thickness resulting in less tubing weight. The sanctioning body rules will determine which type and size tubing to use based on the vehicle weight.
Dependent upon which material is selected for the cage is the welding technique. TIG and MIG welding are the accepted methods. Each have minimal pros and cons but when executed properly, equally strong.
When fabricating a cage, it is recommended to remove all interior unless otherwise stated by your class rules (showroom stock etc.). To start, we determine where the main hoop and harness bar should be located. This is done by sitting the driver and the seat of choice in the car to determine and measure their seating position. The harness and head restraint chosen will also help us determine the harness bar height and location. We then determine the base plate locations on the chassis. Base plates serve as mounting points and have more surface area that gives the cage a rigid platform to stand. The base plate locations are carefully chosen to utilize the stronger sections of the chassis to best support the cage. Once we've determined the main hoop and base plate locations the roll cage construction begins.