From The Ground Up (Advice Thread)

[RogueTwoRobots]

The Robo Challenge 100mm diameter blue wheels have a width/depth of approximately 30mm. There is a boss in the centre of the wheel, protruding out one side. This is where the drill motor nuts are pressed/melted in to. The boss is about 25mm in diameter and sticks out past the wheel by about 5mm, making the total width roughly 35mm.

EDIT: Here's a pic:

[attachment=0:2184e0gr]blue_wheel_dimensions.JPG[/attachment:2184e0gr]