try increasing the spring n' damping, (in meshwheels)
meshwheels2
;tire_radius, rim_radius, width, numrays, node1, node2, snode, braked, propulsed, arm, mass, tirespring, tiredamping, side, meshname material
0.6, 0.329, 0, 14, 33, 32, 9999, 1, 0, 37, 490.0, 450000, 8000, l...