Great skins, thank you for creating. I know almost nothing about creating skins but I think the issue you mention with the tyre textures showing the standard on track is to do with the textures in the 'extension' folder for the car itself. I copied the texture files from your skin folder into the 'extension' folder and renamed them, and this appears to show them correctly on track. I don't know if this is the proper fix, though.
Okay okay, I'll need to try that!