I found that the Dagu wheels used on the WT chassis would be awesome for one of my projects:
They are almost 5" in diameter, knobby, and have a sweet red anodized finish. All the trappings of perfection in my eyes. Anyhow, the hub is my concern. I have a 6mm shaft I want to stuff in its hole but I don't think it will jive. There is a 4mm shaft adapter available but it doesn't look like I can easily modify it to make it work for me.