This plastic servo wheel is made specifically for Futaba servo splines and has a diameter of 2-5/8". Each wheel comes with a pair of black rubber bands: the tire and a spare.
This plastic Futaba servo wheel is made to match Futaba servo splines, such as those on the SpringRC SM-S4303R and Power HD AR-3606HB continuous rotation servos. The wheel is molded from ABS and measures just under 2-5/8" across by 0.3" wide. With the included rubber band tire, the total wheel diameter is 2-5/8". The wheel is available in blue, yellow, red, and black.
For mini-sumo robots, you can also get a high-traction sticky tire made especially to fit this plastic robot wheel.
Two rubber band tires (one is a spare)
For a version of this robot servo wheel that has molded-on silicone tires and built-in encoder stripes, see the Solarbotics SW servo wheels with encoders.