Tutorial, modeling a tyre.
Use the ‘Insert Edge Loop Tool’ and the ‘Split Polygon Tool’ to add edges. Move them around to match the pattern of the tyre as close as possible. When moving the vertices, make sure you click in the centre of the gizmo to ensure that the vertex snaps to the NURBS guide surface. Make sure that you move each vertex at least once. You can start off pretty rough but try and keep the lines that would run around the edge of the tyre straight. It’s also a good idea to keep the segments as evenly sized as possible. This isn’t intended to be poly smoothed so four sided faces aren’t that important but try and keep the edge flows fairly clean.
Once you have a rough shape ready, you can duplicate an instance around in order to get a better idea of what the final tyre will look like. To get the number of degrees you want to rotate the instances by, divide 360 by the number of segments you require. In my case, I get 12. Go to ‘Edit’ > ‘Duplicate Special’ > option box. Plug the angle you just calculated into the Rotate Z box. Make the number of copies the number of segments minus one. Make sure that ‘Instance’ is selected and click ‘Apply’.
Now you can edit the top piece and the rest of the segments should follow suit. It may be helpful to move the reference image of the tread segment to the origin and putting the ‘Alpha Gain’ up to one. This will hide the polygons below it, making it easier to see what you are doing.
Continue to refine the shape of the segment, taking care to ensure that the vertices on either side of the segment line up with their neighbours. You can hold down ‘V’ to snap vertices to their corresponding locations in the instanced geometry. Eventually, you should have no gaps and all the appropriate edges for extruding the tread pattern.
You don’t really need the surface to be live anymore, make sure nothing is selected and click the ‘Make Live’ button.
Select all the faces that make up the tread pattern.
You can hide the surface guides by clicking ‘Show’ in the viewport menu and unticking ‘NURBS Surfaces’.
Go to ‘Edit Mesh’ > ‘Extrude’. Extrude inwards till you get about half as deep as the maximum you want to go. Different grooves have different depths and, in this case, it’s only the wide channels that need to be extruded all the way down.
Select the channels and extrude them further inwards.
Delete the unwanted faces where the channels connect. Make sure the vertices of the newly created polygons line up with their neighbouring segments by holding down ‘V’ again to snap them each individually.
Now it’s time to fine tune the grooves. If you were to just select some vertices and move them up or down, you’d run into problems. This is because you are working on a curved surface. To make sure you’re moving things in the right direction, select a pair of vertices. Click ‘Set to Edge’ in the ‘Tool Settings’ for the ‘Move Tool’. Click on a nearby edge that’s pointing outwards. Now you adjust the vertices in the correct direction.