The mechanism is based on four-bar linkage ABCD with driving eccentric 1 which rotates about fixed axis A. Link 2 has collar b encircling eccentric 1. The end of link 3 is a wheel lug. The other wheel lugs belong to additional links hinged to link 2 and rim 4. As the wheel rolls along the ground, the lugs are periodically extended from rim 4 and then withdrawn again into the rim.