[I've looked at that route on the IGN 1:100,000 map - the contour lines are very close together in places! Another possibility that looks possible is going south from Tonnerre through Ste Vertu and Nitry, across the autoroute, and through Joux-la-Ville and Precy-le-sec to reach the Cure at Voutenay-sur-cure. This misses Chablis, I know , but presumably we can buy the wine elsewhere! Can't carry a lot on the bikes, unfortunately. Or, south from Chablis and over the motorway to R Cure also looks possible?
thanks again