The Kenda K23 s-6 Schwinn tire is a great replacement tire for older 3-speed Schwinn bicycles. 26 x 1 3/8 x 1 1/4 (37-597 ISO) size. 600 grams. 65 max PSI. This tire is an obscure size found on some Schwinn bicycles from the 1960's and 70's. This tire is not compatible with 26 x 1 3/8 (590 ISO) rims, nor with modern 26 (559 ISO) mountain bike rims. To be sure of compatibility, look for the ISO measurement on the sidewall of your current tire.