This little tutorial will be a "bonus chapter" of sorts for my car tutorial since I didn't cover the tires and wheels in it, they're provided modeled for you.
This is the tire and wheel model included with the tutorial, and the goal here will be to improve upon it.
The best bet for printing this out is to use Opera or Firefox. You will have to enable the printing of background colours to get the screenshots to show up.
1. Start a New file using the "Small Objects-Inches.3dm" template.
2. Draw a Degree 5 Curve in the Front view. Detailed coordinates are provided for your information, but it's not necessary to be terribly precise with these curves since you will be able to adjust it to your liking later using history. Do, however, use the Ortho snap if need be to keep the first two points from the centerline aligned vertically.
3. Draw another small Curve, of Degree 3, snapping to the End of the first curve, for the bead--well, the part of it visible around the edge of the wheel.
4. Join the two curves.
5. Command history is turned off by default(with some commands it can cause "unexpected" effects,) so run the History command and set Record to Yes, Update to Yes, and Lock to No.
6. Revolve the joined curve around the origin. The FullCircle option bypasses the prompts for picking the angle of the blend and just does a full revolve.
7. In the Top view, away from the Tire, draw two more Degree 3 Curve objects.
8. Join them.
9. Create an object from these curves with ExtrudeCrv. Make a solid using the Cap option and extrude them down a distance of 0.5 units.
10. Now Draw a Plane in the Top view, around the groove cutter object.
11. Select the guide curve for the groove cutter and nudge or Move it up by 0.2 units, which will move the solid up too.
12. Use FlowAlongSrf to wrap the groove cutter onto the tire. Use the plane as the Base surface, selecting it near the corner highlighted with a point.
After picking the surface of the tire, the result may look more like the image at below left than right. If that is the case, run Dir on the base plane and try the SwapUV and UReverse or VReverse options. The result of the flow operation will update after running Dir.
13. Copy the groove cutter around the tire with ArrayPolar. Array it about the origin and set the Number of items to 13.
14. Move these three points on the cutter guide curve down by 0.5 units and in by 0.2, and make whatever other adjustments you wish to their shape. Note that the way the cutter solids roll around the outer edge of the tire, digging in too deep, will be fixed next.
15. Select the original groove cutter solid and run CageEdit. At the Select control object prompt pick BoundingBox, pick World for the Coordinate system, and at the Cage points prompt enter values of 4 for the number of points in each axis: XPointCount, YPointCount, and ZPointCount. Finally, select Global for the Region to edit. There are a lot of settings, but you can usually click through the defaults for most of them.
16. Cage editing the cutter is going to 'break' the history with the curve used to make it first, so we might as well Delete the curve.
17. Select the outer points on the cage and move them up by 0.38 units.
The arrayed cutters have been updated and should be about ready to boolean.
18. Draw a small Rectangle in the Front view.
19. Revolve the rectangle about the origin to make a radial groove.
20. After making any desired adjustments, BooleanDifference the groove cutters from the tire. Booleans aren't hooked up to command history, so you would have to Undo to change anything at this point.
21. You can now Delete everything but the tire polysurface.
22. Mirror the tire.
This is a pretty simple tread design since it can really drive up your file size quick. Much more detail than this(for illustration purposes)should really be done through texturing. We'll look at that in the rendering phase.