For someone, somewhere, this could be a dream-tire come true: a 650b x 42mm Panaracer Pasela Tour Guard. Whether you've been dreaming about it or not, this tire is a welcome addition to the slowly-growing pile of ~40mm 650b tires. Not a ballet slipper, not an Enduro tread, but falling in between as a durable, light-enough, comfortable, all-arounder tire (the hang tag says "Urban Commuter Tire.") This light-beige wall version comes with a folding bead, so works well as a tour spare shoved deep into a pannier.
At ~40 PSI, mounted on a 24mm-wide rim, it measures out at 41.5mm. Weight is 480 grams.