pic: 2.5in gearbox

[IKE]

If this is for an FRC robot, you may want to make sure the wheel is easily replaceable.
Anecdotally and from some experience, when using the belted wheels, an 8 inch wheel would last most of a season. 6 inch wheels tended to last an event pretty well, and 4 inch wheels I think needed tread change each day.

Aren Hill made a neat little swerve module several years ago that used a small wheel. While the module worked well, I think fast tread wear was a concern of that system.

One other possible critique, you may want to look into narrowing the gears. With the lower relative torque in your system, you could likely reduce the gear widths and further improve your packaging space. If you are using COTS gears, then I can respect the extra width vs. simplicity of application.

It appears as though you have sprockets to run to other wheels. What size chain are you using?