Just had to buy one for my daughter's new bike. The rim size is 16-1.60. My local dealer had one on the shelf for $16.95.
'12 RZR4XP.....heavily mod'd, now driven by the wife
'06 CRF250X (mine)
'06 CRF150F (my oldest daughter's)
'04 CRF100 (my youngest daughter's)
'07 KLX110 (now in storage, waiting on my son to grow into it)
'04 CRF50 (my youngest son's)