
Load the reference image
in the Luminosity-channel and take a note on the
size of the image. Then create a cube and give it corresponding values
in the X- and Y-fields. Set Z to 1. Assign the cube the material with
the default mapping type, UVW -- you want the reference image displayed
on the front of the cube so that you can work from the Front viewport
and with UVW the image will place itself properly.
Then move the
cube 1 or 2 units backwards on the Z-axis. Why?
In the next step you're gonna create a Polygon Object
and start adding points and if you keep the cube at 0 on the Z-axis
you points will be placed visually "inside" the cube.
The points will be created at Z=0 and you don't want that space
occupied by the cube. So change the cube's Z-position
from 0 to 2.

Create a Polygon
Object (Objects>Polygon Object). Nothing in
your viewport will change but in the Object Manager
a new Polygon Object is visible so double-click
it and name it "Segment". Switch to Front
view, zoom in on the profile, make sure you're in Points
mode and that you have Segment as the active object. Now
start adding points by selecting Structure>Add Points
and then CTRL-click the outline of the profile.
Just focus on getting the points down for one side of the profile
since we will later mirror the Segment to get the complete element.
Place the points
at the "crucial curves" of the profile
-- identify what features are giving the profile its shape and place
the points accordingly.

When you have
all points in place you select them all and clone them once -- Structure>Edit
Surface>Clone. Set Clones to 1 and change
Rotation from 180Ú to 0Ú. Click OK.

OK, now you've
cloned your points so don't let go of that selection!
Move the new points on the Z-axis only to -50 (or just type -50
in the Coordinates Manager). All points are at
the same Z-value so moving them all att the same time will be OK
at this stage. Note: the cloned points are the
unselected ones in the image above.

Time to bridge the points. Select the Bridge tool
(Structure>Bridge) or just hit B on your
keyboard. The cursor will now look like an arrow with a small, black
bridge. Click on the first point and start bridging. Check out this
gif if you're not sure on where to start, or read up on the Bridge
tool in the manual.

This is roughly
what you should have by now. Here I've dropped the Segment in a
Symmetry Object just to see how it works. Now it's
time to start slicing using the Knife.

Select the
Knife (Structure>Knife) or hit the
letter K on your keyboard. Make sure that the option
Restrict to Selection is unchecked
in the Active Tools Manager -- we want our cuts
to slice throgh the whole mesh. From the Top or
Right viewport add 4 cuts like in the image: 2
cuts to form a thin band of polygons and 2 cuts to form a slightly
wider band. If you hold down Shift while cutting
you will restrict the knife to 45Ú angles and will make it easier
to keep the cuts straight.

Now switch
to Polygon mode, select the polygons shown above
and delete them.

This is how
it should look.

OK, this can
be a bit tricky but the principle is quite easy: select some points,
clone and move them, and use the Bridge tool to
create new polygons. Here's how you do it:
Select the points on the image marked with purple dots (•)
and copy their Y-value from the Coordinates Manager.
Now select the blue dots (•)
and clone them once, just as we did before.
Paste the values you copied earlier in the cloned dot's Y-channel
and hit Enter -- the points should move down to
the position marked with orange (•).

Now Bridge
the points to build the polygons nescessary for the pattern of the
tire. The image above shows what it should look like.

Continue cloning
points and then bridging them as this image shows. As you can see
I've let 2 triangles slip through but I think we can get away with
it :)

Now it's time
for some more slicing. Select the Top view and
lay down 6 cuts along the X-axis as shown in the image. The cuts
are made close to the edges and the reason for
these cuts is to provide sharp definition when we eventually drop
the finished wheel in a HyperNURBS. When you're
done cutting swith to Front view for some extra
slices.

The black
lines on the image indicates where the cuts should go.
Once again, we want sharp definition on our tire pattern and this
will get us there.

This close-up
is just to illustrate that I decided to go with triangles for the
ending of the thinner polygon band as well. You can also see some
of the cuts we made in the previous steps.

If you drop
the Segment in a Symmetry Object and hit render
you should have something like the image on the right. It has some
resemblance with a tire but we're not there yet. Switch to Points
mode and Top viewport.

Select the
Live Selection tool and make sure that Only
Select Visible Elements is unchecked.
Then select a any group of 4 points and start moving the on the
X- and Z-axes. If you have some reference material
of real tire patterns, use them, otherwise just move and rotate
the points (around Y-axis only!) until you get
something that could pass as a believable pattern.

Frequently
check with the Symmetry Object active and dropped
in a HyperNURB to see how you're doing. When you're
satisfied it's time to Duplicate and then Bend.

Deactivate
the HyperNURBS and select the Symmetry
Object. Then select Function>Duplicate. The
number of Copies determines the size of your tire
-- 5 copies will make it pretty small and 200 will make it pretty
huge (although rather thin...). Anyway, enter 50 to start with and
work from there. Alse check Generate Instances
so you wont bog down your system with too much geometry. Also, if
you change the geometry of your Segment, all instances will update
immeadiately.Now, the tricky part here is to know how much every
instance should move. Select Top view and start
experimenting with different values for the Z-channel.
You might wanna zoom in real close in order to get the instances
to line up properly. I found that something around 2500 was an appropriate
number. Click OK.

Add a Bend
deformer (Objects>Deformations>Bend). Group
the Symmetry Object (containing your Segment),
the Instances and the Bend deformer
under a Null Object (Objects>Null Object).
Name the null Wheel. Select Right
viewport and rotate the Bend deformer -90°
around the X-axis/Pitch. Now double-click the Bend
object to bring up its dialog box. Change the Y size so that it
encompasses the whole group of instances and is placed reasonably
in the middle of the group. Check Keep Y Axis Length
and set the Mode to Limited.

Your hierarchy
should be as the image above illustrates. Now we will bend all those
instances into a circle and forming the actual tire.

Grab hold of
the yellow handle on the Bend
deformer and start dragging it in the Z-direction.
You will see the instances starting to bend. You will probably have
to drag the handle as well as zoom out quite a bit before the circle
will be almost closed. Now zoom in and double-click the Bend
deformer once again. You'll see that the Angle
will be very high and this is the value you should play with now
-- add 10-20 degrees, click OK and see what happens.
Zoom in extremely close on the gap between the
two ends and make sure that they meet as neatly as you can. For
my wheel the angle of 412Ú proved to be OK.

Now drop the
Wheel-group in a HyperNURBS and
render -- Congratulations, you have a tire! Just
add a hubcap and you're ready to roll!

Here I've added some additional cuts (the line along the center of
the tire) to break up the pattern a bit plus a rim modeled by following
this
tutorial by Holger Schömann at Digital
Worlds.
Note: the tire
can get very heavy on the polycountside when you drop it in a HyperNURBS
so if you're not planning any close-up shots of it, deactivate the
HN. Usually you can get away with simple polygons. Or set the HyperNURBS
Subdivision Renderer to 1 to keep
some smoothness.

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