Just took some pics, and to my surprise the Grand Bois Cypres 650B tires did fit the C'dale though just barely (~2mm per side). Here's what that looks like:





Here's the clearance on my Vitus 979--much better!:





And my calipers show these tires as just a hair under 31mm wide on Sun CR 18 rims, inflated to about 80 psi:



Neal