QuadSim is a quad (vehicle) physics demo based on my spring-based soft-body physics engine, written in 2006. All physical interactions are simulated using a variation on simple mass-spring connections. This variation includes a anisotropic static/kinetic friction model. Consequently, skidding of the quad is the result of realistic simulation of the contact friction between the soft-body tires and the ground. The (skeletal) quad model includes springs, shock dampers and non-rigid tires, all simulated using the same algorithms.