Variable speed steering system has been used by cars of various brands, including BMW and Toyota, with the purpose of improving the stationarity and controllability of the vehicle. Until now, relevant investigations are focused on the theory and traditional application, while the geometric characteristics and tooth modification for the rack are left untouched upon, hindering the prospect of a wider application. Focusing on this, the paper synthesizes the mathematical model, geometry characteristics, and tooth modification method for the variable pinion–rack drive. The major contributions lie in the contact analysis and the modification methodology for the pinion–rack drive, which combined forms a solid foundation for the application that has never been discussed.