Step 1. - Reset 3D Studio Max
Step 2. - Go to the Front View
Step 3. - Go to the Create Panel and make a tube. Make Radius1 = 100, Radius2 = 80 and the Height = 60. This is the basic shape that we'll use for this tutorial. It's supposed to be a tire: we'll make a tire (without the alloy) which has some profile AND some letters on the side like this (don't pay any attention to the low ammount of segments, because that can be altered any time. And the inner side is also textured, but that does not matter either since one would usually make an alloy inner tire too...):

Step 4. - Before you even begin to make this tire, you should make the two textures needed to apply to the tire. I would suggest something like the following two, since I already used them and they work very nice for the wanted effect: double texture on this tire. Save these two pictures as tire-side.JPG and tire-track.JPG.

Step 5. - Select the tube and convert it to an editable mesh. Go to the polygonal sub-object level and select the faces/polygons on which you want the tire-track to be applied. When selected go to the material editor and make a new material. Click the maps roll-out and click the bump button, select bitmap from the pop-up and select tire-track.JPG. Set V-tiling to 25 (we need the track to be repeated a lot of times because it has to go all around the tire) and the W-angle to 90 degrees (on the right). Click Show map in Viewport and then Go to Parent . Set bump amount to -999. And to complete this material set the Diffuse and ambient color to (45, 45, 45) and specular level to 45.
Step 6. - Go back to one of the viewports and press Alt, e, i which means Select Invert (or make a shortcut like me: Ctrl + Shift + I). So now we have all the polygons selected which do NOT need the tire-track on them, BUT need letters on them, because they are the side of the tire. So now go back to the material editor and again make a new material. Again click the maps roll-out, and now click the diffuse button, select bitmap and then tire-side.JPG. Again click Go to Parent and set the specular level to 45. Again click Show map in Viewport. Now you should have two materials that should look like this in the Material Editor:

Step 7. - Close the material editor. Go back to normal mode of the tube (= out of the Polygonal Sub-Object level). Apply an UVW map. Click cilindrical. That should do the job nicely, you would say, and I used to think so too. But what happens when we make a test render? IT SUCKS (left image)! Ok, but what do we do then? A planar map! Yes! Again we make a test render... IT SUCKS (right image)!!!! WHOAAAAAA! :) We need both but we can only have one at a time to work... But here is where the map channels come in!

Step 8. - How do they work? Go to the material editor. Select the first material (the tire track one) and click the bump map again so that you are in the bitmap screen. On the right in the coordinates roll-out you see Map Channel. Set it to 1 (it should already be but make sure it is). Go to Parent and now go to the other material (the one for the side of the tire). Click the diffuse button and set the material channel of this bitmap to 2.
Step 9. - Now close the ME. Remove all UVW maps off the tube. Apply a new one: set Mapping to cilindrical and make sure the Map Channel of the UVW map is 1. Now apply a new UVW map, set Mapping to planar and set the Map Channel to 2. Make the Length and th Width of the second UVW 225 (because the tire-side.JPG is a bit too wide and high). Make another test render.... YES! It's good:

Wrap-up - Well that's about it. I explained how the idea behind Map Channels work by making a tire with two materials that needed different UVW maps. An important thing to remember is that the Map Channel of ALL sub-materials have to be set to the right number: suppose you have a material that has a diffuse, bump and opacity map then all map channels within each map have to be set to the right value. I hope that you understand that this is only a simple example of how Map Channels work and that you can apply it in a more complicated way with more UVW maps and more materials.

Applying this technique is also possible without eating up all your material slots (I know that you can have more than 24 that are available... but still), by using Multi/Sub Object materials. This is very simple: everything works the same only now, you would have to set the right Material ID's of the selected polygons. It does make it a lot more easy to comprehend, especially with a lot of different materials on one object.

Help - Here's a piece of text from the Help file that ships with Max. It's explains the definition of a Map Channel:

A map channel associates a map with an object's mapping coordinates.

When you turn on Generate Mapping Coordinates for an object, they use map channel 1. You can assign new map channels with new mapping coordinates by applying a UVW Map modifier to the object. Map channel values can range from 1 to 99.

For NURBS surface sub-objects, you can assign a map channel without applying UVW Map. The surface sub-object has a different set of mapping coordinates for each map channel you use.

A map's map channel value identifies which of an object's mapping coordinates to use. Different map channels allow maps for the same object to use different coordinates. For example, you might use one channel for diffuse mapping and a different one for bump mapping. Map channels also let different maps use different coordinates within a compound material, a compositor map, or a multi/sub-object material.

Different map channels can have different U and V tiling values, different U and V offsets, and so on. In the UVW Map modifier, you can also set different map channels to have different mapping types (planar, cylindrical, spherical, and so on).

If you apply a map that uses a certain map channel to an object that has no mapping coordinates for that channel, the map doesn't appear on the object. When you render, a Missing Map Coordinates dialog appears to warn you of the problem. The dialog lists the map channel and the object name.

---