A roll bar is a device that is intended to protect passengers in a vehicle in the event of a rollover. The roll bar is attached to the frame of the vehicle and bent in a series of hoops fitting inside the passenger compartment of a vehicle. In the event of a rollover, the roll bar displaces the weight of the vehicle and distributes it to the chassis. This prevents the vehicle's roof from collapsing. In a pick-up truck, the roll bar is typically mounted in the bed of the truck and bolted or welded to the frame underneath the bed.
Many of the vehicles driven on the public streets or entered into car shows utilize a show bar. This is a non-functioning system of roll bars to which lights are mounted or that give the illusion of safety. This type of bar is much less expensive to install. The show bar has no structural value and will not protect the vehicle or its passengers in the event of an accident.
The most common type of material used in the fabrication of a roll bar is drawn over mandrel tubing. This tubing is one-piece mild steel tubing and is very strong. In most racing applications, the roll bar is made from chrome-molly steel which is much lighter than drawn over mandrel tubing steel and is also much stronger — increasing the level of protection.
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When fabricating a roll bar from mild steel tubing, a metal inert gas welder is used. This is generically known as a wire welder. This type of welder produces a very strong weld which is also very clean. The metal inert gas welder does not produce slag which must be hammered from the finished weld. On the chrome-molly steel, the weld must be performed with a tungsten inert gas welder. This welder is capable of producing much higher heat and is also better controlled, producing a stronger weld.
In racing applications, roll bars are required to be certified by the sanctioning body of the type of racing that the vehicle is competing in. For drag racing, the roll bar must meet specific requirements for the speed at which the vehicle is capable of operating. For off-road trucks, the roll bars must meet very stringent standards for the protection of the driver and the co-driver. The roll bars must also meet the chassis at very specific locations to ensure vehicle structural integrity.