[UV unwraping]Why do we always put car wheels on a separate UV map when unwrapping

howardding2000

Hi, I am learnning 3D modeling. I've been working on a car lately, and I'm basically done with the modeling , and starting to unwrapping UVs. I was originally going to put part of the car frame and the wheels on one UV map, but my teacher recommended that it would be better for me to put the wheels on a separate UV map. It seems that most people are doing this. My teacher explained that the wheels mostly rotate, and that the AO of the other parts may affect the wheels. But I don't really understand it. Can someone please explain it to me in more detail? Thanks a lot!

Neox

I have no idea how these parameters influence each other. 
I mean yes you could have AO hit the wheel theoretically. But that can be the case independent of their UV Map.

You could either explode your model for baking or use baking groups, or name matching to avoid said issues, doesnt matter if it is on its own texture or one combined.

Klunk

you could have separate mapping to fake wheel rotation by transforming/rotating the uv's on the diffuse and normal then you can have the "static" AO map (on different map channel) on the wheels without the obvious ambient shading going around and around.

dimwalker

I used variation of exploding method - fifth wheel that is away from the car, just far enough to not get affected by chassis. Other wheels have their UVs moved 1 tile away so they won't affect baking, but use same texture area.

Imho only good reason to have a wheel on its own texture is to allow more details/pixels.

Klunk

I guess, if your game has "pimping" then all the wheels would need their own  texture or all wheels on the same texture even.

Eric Chadwick

Another trick is to bake AO for the whole model on a 2nd uv, then adjust the wheel material to use an AO strength of zero. This wastes a bit of uv space if those surfaces are never used by the AO texture, but the AO can be enabled easily for garage shots, like when the player is customizing the car.