VEX-WHEELKNOBBY VEX Robotics 5in. Knobby Wheel 2-Pack <p><font color="00ff66" size="2" face="Arial, Helvetica, sans-serif">A set of two Knobby Wheels, as seen in the <a href="VEX-276-2151.html" target="_top">VEX Robotics Design Starter Kit</a>.<br> 5" knobby tires with 4" hubs.</font></p>
I have bought 4 of these wheel. I think they are good quality, plastic seem to be robust but rubber (tires) is a little to hard... Axis holes are square so, I have drilled it (5 mm). All is ok, but you must use a drill press.
$10.99 
VEX Robotics Wheel Leg Kit (Whegs) 4-pack
VEX Robotics Wheel Kit
VEX Robotics 4in. All Purpose Wheel 2-Pack
VEX Robotics 2.75in. Low Friction Wheel 4-Pack