Weight is generally referred to as a bad thing in auto racing. Sure, the heavier your car the slower it will be, but weight is something that can be managed and even used to our benefit. Luckily, your competitors also have to deal with the same amount of weight in their cars. The difference is in who uses that weight to their advantage.

Weight equals grip: The weight pressing the tires into the tarmac gives your tires grip. However, too much weight pressing the tires into the tarmac will cause the tires to exceed their grip levels. A dragster puts as much weight as possible on the rear tires, the only tires that really matter in that form of racing. Having all the weight to the rear will push the rear tires firmly into the track, offering the most grip. Lucky for them, they are not racing around a corner because once that drag-race car begins to corner, all that rear weight will cause the rear tires to exceed their lateral grip capabilities and the car will spin out. 

Any race car driver who turns has to deal with weight at all four corners of the car. We do want ideal straightline grip to the rear tires, like our dragster above, but we also need the car to make it around the corners as quickly as possible. Being able to adjust the weight bias forward and rearward can help us achieve both of these goals. Generally, an ideal road racing car will have 50/50 weight on the front and rear. Still, the more weight shifted to the rear will allow better cornering speeds (less lateral load on front tires) as well as better acceleration out of slow speed corners (more weight pressing the rear tires into the track). The down side is that the rear of the car may become less stable in higher speed cornering.

Left-to-right weight changes can be used at specific tracks with predominate left or right hand corners. An example of this type of track is Lime Rock Park where all but one corner is to the right. Oval racers put as much weight to the left side of their cars as their oval race tracks are left turn only tracks. 