The GMPW wheels are made to match the Solarbotics
and GM7, 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 band, the total wheel diameter is
2-5/8". The wheels are available in blue, yellow, red, and black.
The wheels are currently somewhat expensive, but
combined with one of the corresponding gearboxes and motors, they are a
good value. You can get a pair of gearmotors and wheels for £20, which
means that for less than the cost of a pair of servos, you can get the
entire drive system for your robot.