i would like to unwrap a simple tyre with a lot of details, trying to avoid huge distortion and i'm not able to figure out how i could do it. I would need to figure out the unwrap of the lowpoly but also of the higpoly version. Somebody has a suggestion?
Since this is a repeating pattern, start by preparing a clean unwrap of one tiling segment (one checkerboard section).
This is using a Mirror Modifier to generate symmetry on the X axis, and an Array Modifier using Object Offset to get the rotation angle from an Empty. (In the modifier settings, enable Merge.)
Note: Shape Keys cannot be applied to a mesh that has modifiers. With this in mind, you can Apply the Mirror Modifier before creating your Shape Key if you want to... but since the left and right sides are the same this will equate to about twice as much work than is necessary. Instead, we can flip the UV unwrap result later - which is the approach I'm going to take in this example.
You can create a Shape Key to deform your mesh non-destructively, for very precise UV unwrapping. Make sure your newly created Shape Key is selected before you jump into Edit Mode and start working on the mesh.
How you get your mesh into your ideal shape for projection is up to you. In my example I started with Smooth Vertices.
I've marked the seams around the extrusions just to make them more visually obvious and easily selectable while editing here.
Tip: You can select a seam island by selecting a single face inside it and then doing Select Linked (CtrlL). You can then Grow (Ctrl=) or Shrink (Ctrl-) that selection if desired.
Then, with my Pivot Point set to Median Point, I selected each edge loop and scaled it on an axis to straighten them.
The vertical edges can be straightened on both X and Y simultaneously if you press ShiftZ (to omit only Z) while scaling.
For uncurling the curved geometry of the tire into a nearly flat shape, you can use the 3D Cursor as your Pivot Point and Rotate the mesh in sections, deselecting as you go.
Above: Using Circle Select and Rotate to straighten geometry.
Using these methods you should be able to get your UV layout exactly as you want it.
This takes a little time, but it's worth it if you want to get a really clean grid of a UV layout.
(Note that the Follow Active Quads projection method often works well for simple grids, but it won't handle the topology of these extrusions well.)
In Edit Mode, facing the direction you want your UV layout to be projected in (in my case Front Orthographic View), press U and choose the Project From View method.
In the UV Editor, select your unwrapped result and move it precisely to the bottom left corner of the UV Editor's square area. Zoom in as far as possible to make sure it's right on the edge if you want a perfect flip with no gaps.
I didn't devote much attention to UV stretching in my example here, but now would be a good time to make a preview material for your model with a simple "color grid" texture, and see which faces should be scaled up or down to make optimal use of your texture space.
If you think you might need to make small adjustments later, you can assign parts of your geometry to Vertex Groups to make them easily selectable. But of course making adjustments to the original geometry beforehand is best.
Save As. Next comes a destructive edit. Delete the shape key you used for unwrapping. Then delete the "Basis" shape key. Now you can Apply the Mirror Modifier.
In the UV Editor, enable UV Sync Selection by clicking the button with two arrows going in opposing directions.
Now when you select the other half (Mirror Modifier result) of your mesh, only the 3D Viewport's selected geometry will show as selected in the UV Editor.
Set the UV Editor's Pivot Point to the 2D Cursor.
Check that your 2D Cursor is precisely in the bottom left of the UV area (this is its default position, but you can check in the View tab (press N if you don't see it). It allows you to specify the X and Y coordinates of the 2D Cursor.
Now with the mirror result part of your mesh selected in the UV Editor, Scale
-1 along the X axis.
Next, select the entire UV map, Grab (G) then move it along the X axis by
1. Everything should now be centered and you can Scale it to get it right in the bounds of the UV area. You will need to position the 2D Cursor at
0.5 on the X axis.
Remove the marks from the seams we used before. Mark Seams only on the edges that will be the boundary for this repeating segment of the tire.
If you want the UV map to be for just one segment - you're done. But I'm guessing you probably want it to cover the entire tire so that any textures you give it will look unique and not repetitive. In that case, keep following along.
Save As. Apply the Array Modifier.
Now for the final steps of the process. Select Linked (CtrlL) the newly generated geometry from the Array Modifier result in the 3D Viewport and in the UV Editor move the UV island up on Y so that it touches where the last UV island leaves off. (It helps if you set the Snapping method to Vertex, or if you've scaled it to some rounded number so you can key in the distance to move it by.)
You can then repeat this process, adding a new Array Modifier, adjusting its setting and the rotation of the Empty, Applying it, and then placing the newly generated UV islands.
The final time you use the Array Modifier, to go "full circle", check the Merge settings and enable First and Last Copies. This connects the last array segment back to the first one.
Once you've got your UV islands laid out the way you want them, consider adding some margin. Scale them in a little bit so they don't touch the outer edges or each other.
Here I marked the region where u should put the seams, If ya want to avoid distortion, I know the Treads part will give distortion bcz of the sides. What you should do is get an addon called UV squares it's free and select the side loops of each of 3 tread islands and make it straight using UV squares addon.As in second images It will work. you might need to do some pinning also to get good shapes. if ya can send the model maybe I can explain the process more easily Second method is making those tread square each islands which is far easy but not efficient