In this tutorial I will try to explain how you model a tire thread.
First of all you search the web for some good reference shots, www.smcars.net is a good place to start. They have loads of good reference shots needed to model an entire car.
If you have a good reference you place this into the background of the top view. You do this by going to 'Top view" ( hit F2, at least in my case it's F2 ) and then choose the "Configure" option under the "Edit" menu. You will now see the Attribute manager change. In this manager go to "Back" and place the reference shot in the Image field. You should now see the image appear in the background of the viewport.
Now that we have our reference picture set up w can start modeling.
First of all you should create a new polygon object. I started by just using a plane size 800 x 100 with 1 subdivision on both sides.
You can continue by making the polygon editable and cutting it in the necessary places. These will have to be the same as your reference pic. If you look at mine you can see how they should look. ( Don't worry if they aren't 100% spot on, we need to move them anyway. )
As you can see I deleted one half of my tire and used a symmetry object, this will save you some work when moving the points around.
Well as I said before we have to move the points so they match the reference picture. You simply select the points and move them to where they should be. The result I got is shown on the pic. You will also see that I extruded the outer edges to fit the reference pic, simply do this by selecting the edges and extruding them.
Well now that we have the basic shape of the tire we can extrude the polygons that need to be extruded. The height isn't very important, just make sure it looks realistic . You might also have to stitch some points together to make the little slope that is in a tire. You can simply do this by using the "Stitch and Sew" tool.
As you can see these few steps give us the basic part of the tire thread, now we will copy this bit a few times to make a rolled out tire.
We do this by going to the "duplicate" tool located in the "Functions" menu. Make sure you selected the polygon when you set up the tool. For my tire I had to copy it 104 times along the Z-axis, the distance between the copies is the length of the polygon. If you don't know the excact length you can always use the "measure" tool in the "functions" menu. Once you have this measurement you add a bit to it. ( You'll see why later. ) Also be sure to select the "Create Instances" this will be a great help once we have to edit the shape a bit. Ok now hit Apply.
As you can see on my example the points might not align very good with the copied part. Since you copied instanced you can simply select these points and move them closer to the other part. Do this as close as possible because this will help you a bit later.
Click to enlarge
Once you made these changes and the points are aligned we need to make these copies into 1 shape. So go to the Null object called "Plane-copies" and select children. Make sure you l-also selected the basic polygon you used to make copies and now connect them. A new object should appear and it should look something like this.
Click to enlarge
Now we can use a little trick, just co to the "optimize" tool when you right click in the viewport, make sure you have point mode enabled. Zoom in a bit and play around with the tolerance distance. When I placed mine on 5m the point of the copies jumped together. I tried to show this in the next picture.
Click to enlarge
Ok now that we have the rolled out tire we have to roll it up.
To do this we use the "Wrap" tool located in the "Deformation" part under "Objects". You place this as a child of the thread and after playing around with the settings you should come up with something like this. ( Make sure the tire closes nicely, cause we'll have to use that optimize trick again later on )
Ok the next thing you need to do is make a copy of the tire without the wrap tool. We do this by going into object mode, selecting the tire and choosing "Current state to object". This will create a copy of the roll up tire without the wrap tool in it.
The next thing we have to do is closing it up. So we go back to point mode and do that optimize trick again. The best way to do this is by looking at the part where the 2 ends meet. You play around with the tolerance again until they weld themselves together. This is the bit where it's important not to have made the gap too wide, because if the gap was too wide you will weld points together that didn't needed to be welded.
If you now select the outer edges and extrude them a bit and replace them you should come up with this result.
And add a rim ro it and you get this.
I hope you could follow these steps and you also get the result you should. If you have any problems don't hesitate to ask.