Q: What does a sway bar actually do?

A sway bar ties the left and right wheels together through a torsion spring, so when the body leans in a corner the bar resists that roll and keeps the tire contact patch flatter on the road. Less roll means quicker response to steering and more consistent grip. On a Tesla Model 3, which carries its battery weight low but still rolls noticeably, a stiffer bar sharpens turn-in without changing ride quality over bumps.