Described in its simplest form, a birdcage is the working foundation of a 4-bar (4 link) chassis suspension system. It stabilizes and regulates the movement of the rear of the car. It also provides a platform to control the moving relationship between the chassis’ shifting weight and the car’s rear traction. Sounds easy enough, right?
The things about your car that a birdcage controls are crucial to your car’s performance. You will never outrun everyone else until the birdcage is at least close to right. The better your birdcage setup is, the better your chances.
This information comes from PPMRacingProducts.com. Check out the full article, with diagrams to better explain birdcages. https://www.ppmracingproducts.com/birdcage-setup/
Below are some examples of what birdcages look like. To see one in action, check out the video below the images!