Nice! looks kinda familiar! Haha =)
I see you're going "clamp style" for tread, but you need a little groove along your rim that captures the tread so it doesn't fall out (higher quality picture here where you can see the groove better
http://604robotics.com/Blog/wp-conte...2/IMG_0296.jpg). I like how you made both halves symmetrical for ease of machining, however, what we do is make them asymmetrical so you can have a locating groove instead of using the screws/axle to center the two halves.
Also, you might be able to get away with less spokes. 7 is a cool number.
Keep up the great work!