There's probably so many ways to do hub caps it's barely worth covering... I'm interested in advancing the cause of HyperNURBS though, so I will cover a method of doing them that incorporates the traditional approach of lathing with the advantages of HyperNURBS - efficient polygon count and easy manipulation.
Use a linear spline to define a very angular profile for lathing a hub cap with. The idea in mind is to retain control over the basic shape of the lathe, but by using an angular spline and low rotation subdivision, we can effectively create a low polygon cage for dropping into HyperNURBS to smooth and edit further.
Note, you may have to rotate your spline object and object axes to get the lathe object oriented correctly for our purposes.
Drop the spline into a Lathe NURBS object, and choose a fairly low rotation subdivision. For this hub cap, I have chose 12 rotation segment. Depending on the style of hub cap you are going for this approach can vary widely. Since I'm doing a vintage model car, I want my hub caps with a suitably retro style to them. The idea I have in mind will entail a few holes ringing the outer portion of the hub cap, so I need suitable polygon structure. If you were doing a modern sports car, maybe you'd want some of those three spoked mags on it, and could get by with only six rotation segments etc.. Again, study the shapes you want and take what you've learned from the HyperNURBS planning I was babbling about earlier and then plan out your geometry accordingly.
The Lathe NURBS object is dropped under a HyperNURBS object and you can see the angular look melts away. Next, make the Lathe NURBS object editable, so we can get at the polygon structure and do some editing!
The basic shape of the hub cap suits my purposes pretty well, but I'm interested in adding just a bit more detail.
Namely, I'd like the outer portion to have a few holes in it to break the monotony of solid chrome.
Using the polygon tool, I select the ring of polygons that make up the surface I'm going to add the holes to.
I've decided that editing those polygons directly would result in holes are perhaps a little large for my tastes, so I want to divide this surface into smaller polygons.
I used the extrude inner tool to create a ring of polygons within these polygons. Make sure that you have the 'preserve groups' option enabled in the Active Tool Manager for the extrude inner tool.
Because the circle of polygons is continuous, the effect of the extrude inner tool with this option enabled is to offset the edges of the polygon group selected, creating a separate ring within. I then ran the extrude inner tool again (very minutely), to offset yet another ring of polygons within that narrow ring. This makes the polygon ring quite a visible transition when rendered.
Now I've turned my attention to the top ring of polygons from the original surface, and selected them all. I want to extrude inner them, too, before I begin punching them out to make holes, but how to get each polygon to extrude inner without doing them on a one by one basis?
Easy. Uncheck the 'preserve groups' option in the Active Tool manager for the extrude inner tool and each polygon is treated as a separate entity when the tool is run.
After running the extrude inner on the polygons I have the separation between them I need in order to make distinct holes.
Now I can simply keep those same polygons selected and continue. I extrude a small amount twice towards the back of the hub cap, to give illusion of thickness to the cap (if examined closely!)... then I hit the delete key to get rid of the originally selected polygons and make these indents into holes!
A render of the whole thing shows that it could conceivably be interpreted as a car wheel... which I guess is what we were after!
I've included the wheel file for you to look at if you'd like...
I haven't included the chrome texture, as I haven't asked permission to distribute the maps! You can find the material this one is based on at Deepshade. It is Paul Sherstobitoff's "Gold & Chrome" creation from the first 'minerals' page! While you are there, send in a material or two of your own...
That concludes the wheel portion of the tutorial...
Now we've got tons and tons of little trim, and parts, and accessories, and details to add. Thanks for your patience, I'm typing as fast as I can!