Does the Inner Tube Size Have to Match the Tire of your Unicycle?

As regards the inner tube we have to verify first the diameter (20'', 26'', 29'' wheel etc.).

Consider that if we call a wheel 29, the size "29 refers to the diameter of the wheel including tyre and rim, so the rim will be 28" and will require an inner tube of 28.

Very important is also the width. In the technical data the second number tells us the width of the inner tube. Here's an example:

20'' x 2.125  ►  20'' is the diameter  ►  2.125 is the width
 

Tubes and tires don’t need to match exactly. Tubes are made from butyl rubber which can stretch. Inner tubes will accommodate a limited range of sizes. 

The nominal sizes often do not correspond to the real size of the tire, and the adaptability of the inner tube is quite high.

Sometimes you see inner tubes that are smaller than the tire on which they are mounted to have a lighter wheel, but also larger tubes to look for greater strength.

It’s always best to try and match as close as you can, but there is some flexibility. Having a slightly smaller or larger tube will be quite fine. 

Conversion table wheel size
 

For more info about the rims please go here: RIMS