We did this for much the same reason we did the 26” trucker. For smaller sized riders, the smaller wheel size offers less of the hassle (toe overlap, standover clearance, etc) of the larger 700c size. This also allows us to offer this in the smallest size Surly yet, a 38cm frame. The build kit is pretty much right in line with the 700c version, we will offer completes in 38-52cm and frames all the way up to 58cm. The original thought was we would only offer these in the smaller sizes, but those of us in the brand that test road the prototypes (large and small) loved the ride feel of the bike so much, we wanted to make sure it was available for larger riders as well (for us really, but from our selfishness you may benefit if this is the kind of thing that your rocks are gotten off upon).
With the 650b Straggler also comes the 650b x 41 Knard. Same awesome tire, now in yet another size. You’ll know that we’ve all started riding Bromptons the year we come out with a 16” Knard.
Source: Surly blog