I have a 16" unicycle with a tire size that is 64-305 16X2.4 and I had wanted to put on a tire but I noticed the new tire is 57-305 16x2.125. I’m assuming the newer tire is the wrong size and won’t work on the rim or with the tube…would my assumption be correct?
The new tire will work fine. it is just a bit smaller.
the second number (305) in the tire size is the important one, it is the bead seat diameter and determines which rims will work with the tire. The first number (64 and 57) are just the tire widths in mm.
re-using your old tube will be fine also as the tubes stretch to fill the tire.
I ended up putting the unicycle together with the larger tire, but I will take it apart again to put the smaller tire on. Thanks for the info, much appreciated. 