In this tutorial I will take you through the steps to model the tyres like the one I had earlier made on for Alfa Rome GT model.
What you will need first
A sketch of the tyre, like this one (PIRELLI P6000). For the dimensions of the tyre, let’s use a 205×60r16.
From the dimensions of the tyre we calculate that:
The width of the sketch image is 205mm
The external diameter of the tyre is 16inch + 2 * 60mm = 16*25.41+2*60 = 526.56mm
From the image size (in pixels: 500*190),
we calculate the height of the image (a part of the tyre thread) is 205*190/500 = 77.9 mm
As the diameter of the tyre is 526.65mm, its perimeter is 3.14159265 * 526.65 = 1654.52.
So, on our tyre thread, we can put N times the sketch image with N = 1654.52/77.9 = 21.239. Because the image will be tiled, we need to change the fractional number (21.239) to a whole number. Let’s say our sketch fits 21 times around the tyre.
So, we’ll create a 21-edge circle and extrude it to have one face fitting well over the sketch. Next, we’ll model one element (1/21 of the full tyre). Multiplying it 21 times, merge, and voila!
Step1. Scene setup
Open Blender. Erase all elements of the default scene.
In the Right view (NUMPAD 3), add a Circle mesh of 21 vértices. Rotate it to have one of the bottom edges perfectly horizontal (tip: align top, opposite vertex with the Z-axis.
As the Blender default Circle's radius is 1.414 (square root of 2), size it by 0.707 (1/1.414) to have a radius of 1.0. Then, size it by 0.526/2 = 0.263 (tyre radius in meters) and move all vértices up by 0.263 (the radius).
It’s OK that the bottom edge is not on Z=0. We’ll see why, later.
Duplicate this bottom edge; separate the duplicated vértices to have another object. Extrude it along the Y-axis by 0.205 (the width of our tyre). You now have a Plane and a Circle like these:
You can chek that your worque is OK by displaying edges length: you should have 0.205*0.078 for the plane. One more step and you’re done: duplicate the Plane, change one to display only as Wire (Drawtype in Object panel, F7) and then, select the other one. Switch to UV Face Select mode, go to the UV/Image Editor and load the sketch image. Return to 3D view and Object mode. Activate the Textured draw type (Alt+ZKEY), you get the following:
The sketch is displayed correctly, without any distortion: the few math calculations we did before starting Blender were not useless.
Step2. Modeling in parts
Select the Plane that we set to display as Wire. We’ll worque on it to model a sub-part of the tyre thread. First, use symmetry to save yourself some work. The sketch we have can be split along both the X-axis (radial cut) and the Y-axis (axial cut). So, you can subdivide the Plane one time. But before you do, carefully read the following.
When splitting your edge along the Y-axis, no problem. But when splitting along the X-axis, remember you’re not working on a Plane but a section of a cylinder.
That’s why the bottom edge of the circle is not at Z=0. Let’s experiment to get a clue. If you've already subdivided the plane, please undo it.
Then cut the face (CTRL+RKEY) at percentage 1.00. Don’t select/deselect anything to keep the new vértices selected.
Then, rotate carefully these vértices around the Y-axis (RKEY then YKEY) to get them at X=0 (as seen from the Top or Right view) And in the Right view (NUMPAD 3), you can now chek that these vértices are almost at Z=0.
Remember this move: when cutting along the X-axis, do not move edge vértices along the X-axis, but rotate them around the Y-axis, to move them around a perfect circle.
Just a little note: you have to move the Plane, textured with the sketch, downward to get the added vértices above it (so they’re still visible).
Now you can continue with modeling. Remove 3/4 of the plane as said above, and cut the plane according to each detail visible on the thread. You should get something like the image bellow.
As you can see, cuts in the plane are mapped on thread details, but not on the round details.
To solve it, just rotate them around the Y-axis. This time round details are OK.
As you can see in the Right view, the tyre element is not a Plane but warped around a circle.
This is why it’s so important to rotate vértices around the Y-axis instead of translating them along the X-axis.Now, we will cut the edges in darque areas, to materialize the hollows of the thread. You should obtain this:
It’s important to keep the edges circling the darque areas! We will see why later. Now it’s time to optimize our mesh a bit. We have to remove all unneeded vértices and edges in white zones and on borders. Doing this will allow us to save a lot of polys on the completed tyre (remember, we will duplicate this part 2*2*21 = 84 times !!!).
The vertex count goes from 144 to 78 and, the face count goes from 53 to 22.
Step3. Adding some thickness
Time to model the hollows! From the previous step, select all vértices.
Step4. Completing the tyre
SpinDup the element you patiently modeled (1 turn, 360? of course, 42 steps: because we need 21 elements and the mesh we have is only a half). Once SpinDup is done, you may observe your border vértices are not perfectly duplicated. So, select all vértices, and Remove Doubles (set threshold to 0.001).
You now need to mirror the tyre. Select the row of vértices at the middle of the tyre, and move the 3D Cursor to selection (to have it at the tyre's center, in the middle plane of it) Duplicate the half tyre, don’t move it, but rotate it 180 degrees in the Top view (around the 3D Cursor). Rotate around the Y-axis to align the middle vértices to the ones of the other half tyre.
Merge, and you’re done!
I advise you to use this mesh with AutoSmooth on, to have solid thread details as well a smooth side. Here are some Yafray renders with a rim (blak tyre material courtesy of Sonix's Car Material Library).
Thomas Baron is a software engineer for aeronautical industrty in France. After discovering Blender in 1999 he has been a serious amature user for two years. A car enthuisast alos likes to worque on planes.
By Thomas Baron