As noted above, Sun offers the CR18 with a 540 BSD (aka 24 x 1 3/8). Be careful about sourcing, because they also offer it with a 507 BSD (aka 24 x 1.50).
http://sun-ringle.com/wp-content/upl...chart_2012.pdf
Amazon has some ISO540 tires.
Last edited by nfmisso; 01-06-14 at 04:25 PM.