Door bars are a set of horizontal steel tubes that are intended to protect a race driver in the event of a side impact, or a T-bone impact. Door bars are sometimes called "NASCAR-style" because the design first appeared in the 1960's in Grand National competition, what today is known as the Winston Cup. NASCAR racing is very close, with little escape room, which produces lots of impacts. The bars proved very successful, so much so that they have been copied by virtually every other form of racing where the cars uses the stock unibody tub or full tube frames. Door bars are required by the SCCA's General Competition Rules, or GCR in all production and GT class cars, and optional for Improved Touring Competitors. The bars are ubiquitous in all forms of stock car racing and in the European and Australian Touring Car competition. About the only professional form of stock-bodied motor racing they are not required is in road rally, where the timed start makes metal-to-metal impacts rare.

Door bars extend from the fowardmost up tube to the rear tube of a roll cage. Usually the bars are formed in the shape of a dish, with the curve extending into where the door mechanisms- windows, locks, etc, would be in a stock automobile. At least two sets of vertical tubes tie the bars together with each other, and either the floor or bottom tube- preferably the latter-- of the car's roll cage.

Door bars are not found in formula cars, sprint cars or other forms of racing where the driver sits inside the frame. In these cars either the frame rails or the monocoque tub are expected to provide driver protection.

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