Go by the ETRO numbers on the side.. metric.

FWIW, Conti, Travel Contact is their adventure touring tire .
a fringe of knobs on a smooth center band,
for un paved loose roads they contct the dirt when it's softened,
not in hard pavement. Gator skin sidewall reinforcing .

the smooth center rolls really nicely on the highway....
only made in 1.75" 559-47 [or 622-37]