These 69mm Diameter (2-5/8") plastic wheels are made specifically for the Solarbotics GM2, GM3, GM8, and GM9 gearbox output shafts. Each wheel comes with a pair of black rubber bands for a tire (and a spare).
These black GMPW wheels are made to match the Solarbotics GM2, GM3, GM8, and GM9, gearmotors. These plastic wheels are molded from ABS, and they measure just under 2-5/8" across by 0.3" wide. With the included rubber bands, the total wheel diameter is 2-5/8" (69mm).
Combined with one of the corresponding gearboxes and motors, these wheels are a great value. You can get a pair of gearmotors and wheels for $21, which means that for less than the cost of a pair of servos, you can get the entire drive system for your robot.
For a version of this wheel that has molded-on silicone tires and built-in encoder stripes, see the newer-style GMPW wheels.
We also stock sticky tyres to give your robot extra traction: