Ballast weight is added weight positioned on a race car chassis to aid its handling characteristics. Lead weights, known as ballast weight, are positioned around the chassis of the vehicle to both bring the car up to the required weight and to place the weight where it will do the most good. Depending on the style of racing, the ballast weight may be attached to the chassis in a high or low position on the vehicle. The weight is typically lead, shaped into bars, that is drilled to fit over threaded rod and bolted to the racing chassis.
Race cars are required to meet a specific minimum weight in order to compete in a given class, and the cars' weight rules are usually dictated by the racing sanctioning body or the race track. In order to create a well-balanced race car, the builder will commonly build the car under weight and use lead ballast weight to bring the car up to standard. The advantage in this is that the builder is able to place the weight in a specific location to improve the driving characteristic of the vehicle. Racers have long known the advantage in moving weight around a chassis to increase performance in a given area. The style of racing will dictate the location of the added ballast weight.
Asphalt racers typically mount the weight as low as possible on the race car chassis to promote good cornering and driving traits. Dirt racers, however, typically place the weight as high as possible on the chassis to promote body roll and superior traction and driving ability. The weight is also generally placed with an inside weight bias and also placed to promote a good balance between the front and back of the vehicle. When ballast weight is added by a sanctioning body as a penalty, it is commonly placed ahead of the flywheel of the vehicle to create a nose-heavy race car that is more difficult to drive.
Some drivers have been known to add aluminum bars on a chassis in order to confuse their competitors as to the location and amount of ballast weight the car is equipped with. As a rule, most sanctioning bodies require a racer to paint the ballast weight white and place the car number on each bar of lead. This is intended to not only make a dropped ballast weight bar clearly visible for other drivers on the track, but the number makes it possible to identify which car the weight fell off of — the team could be penalized for the loss of the weight.