Schwalbe makes the toughest tires in the world, and this one here is one they made at our requestand we're delighted. It's the standard Marathon tread and casing and everything else, with a Kevlar belt, wire bead, no nonsense. Schwalbe calls it a 40 or 42, depending on how you read the label (click to the photo of it), and it actually measures a hair under 37 when fresh and new. Tires stretch some with age, so call it a true-enough 37mm.
In fatness it fits right between the Panaracer Col de la Vie and Fatty Rumpkin. It's heavier than both by far, and how do you pick? Here's a good way:

- Fast cushy road riding? Col de la Vie.
- Mixed road and trail, with bumps? Fatty Rumpkin.
- Day-in/day-out tire for any pavement, commute, tour? 650B Marathon.

It weighs a Friar Tuck-like 684g. It will never wear our. It will never get a flat. That's not a promise, just a prediction, but it is a Schwalbe Marathon, after all.