Basically, where is 0% displacement? Is it at 127,127,127 (RGB) that allows for negative and positive values, or does it start at 0,0,0. The reason I'm asking is because I'm considering texturemapping things like tires, since modeled surfaces like that are real poly-bombs.

Someone, correct me if I'm wrong but using displacement maps would probably require just as many polys as (if not more than) modeling the tire since displacement maps usualy need a high number of polys to shape the geometry. Although with subdivs you can generate those polys on render so you don't need to worry about them during modeling or animation.

I'm not positive about your question, but I think 127,127,127 is neutral because 0,0,0 pushes inward.

For coarse treads, like on a tractor, I'll do some low poly vertex modeling and then use Carrara's sub division smoothing.

Dwarg, using displacement mapping does increase poly count, but only when you enable it. So, you can still work with a fairly lightweight model and then click a switch at the end.

Athought it may be true that displacement creates more polys at render time, I'm looking for a much lighter weight mesh for the actual models themselves. (A tire w/ fully modeled tread can have upwards of 50K in itself. Not exactly the fastest thing to setup for staging.) So what MarkBremmer said last is exactly what I'm looking for. Also it's good to know where the midground point is, that way I can get going on texture maps w/o too much wierdness and trial & error.

Has anybody tried to use displacement on shader domains yet?
When I first got C6, I was working on a motorcycle model I had purchased for Poser fro Vanishing Point. It had its tires set up as shader domains, so I was not able to get the tread to truly work and had to settle with simply using a bump map and clever coloring to make it "look" right.

Joe

 6.1 does. :D

 How is this implemented with 6.1?
When I try to setup a Displacement, it's ether the whole object, or the whole object.

 Your object needs to already have shader domains in place. Then, in the usual fashion, you can apply shaders to each domain separately.

There is a cool pass-through feature of Carrara shaders that allow a master shader to be applied to an object but "empty"  or None designations in the domain shaders will inherit the master shader's settings.

 Yes, I got the domain naming and UV mapping down. What I don't get is that the displacement section of shader UI does not allow to name a specific domain. How do you access the specific domain that you want the displacement to take place on?

There are two ways you can do this.

1. select the object and open the shader editor. On the right side of the screen you'll see a bunch of shader "slots" for the various domains. Simply create a shader with the characteristics that you want and load it into one of the slots. This way the object "subscribes" to shaders and leaves you free to also use those shaders on other objects with domains.

2. The other way is select the object, open the shader editor and then convert the shader from Mutichannel to Layer List. You can keep adding shader branches by clicking on the plus sign in the left colomn and then assigning domains and an  shaders at will. This is a faster way to construct a shader for a single object but prevents you from using the shader branches on other objects. That's where the first method is strongest.