These wheels are EXTREMELY light. They are very thin. They are not strong at all. One hit by an opposing ant-weight robot, and your wheels will be shot. I was testing them out between my new one-pound undercutter and my old one-pound undercutter robots, and the wheels fell apart too easily. Do not use the wheels for combat, BUT I suggest you weigh in with them for an ant-pound or fairy-weight robot competition. They did in fact save my life in that respect. I was over weight by about 30 grams. I popped these wheels on and BAMMM I was instantly underweight. They actually drove pretty well when i was undergoing initial weigh in and registration and arena warmup, but after that I changed my wheels to Lite Flites for the actual competition.
PROS: very light. good for weighing in a robot with.
CONS: not strong enough for combat. thinner than you want for good traction.
$2.39 
GWS Light Weight Foam Wheel 51mm Diameter 2pk