Well, it's fairly simple, First, modify the grid properties to fit your needs and select snap to grid (ctrl+j) . It will make things much easier . Draw a circle as the cross-section of your spline object . Center it . Then, choose a symmetrical extrusion envellope in the geometry menu . Now, all you have to do is to add points on one extrusion envellope (blue or green lines) to draw the "half profile" of the tire . You'll notice that when you add points on an enveloppe, the others will change accordingly because the envellope is set to be symmetric . Here it is ! I hope that helps . litst