If you are contemplating the Loire, buy the Bikeline map in Austria or Germany. I delayed buying a guide to the southern Rhine until I got to Strasbourg (to save weight), and could not find it in any bookstore or cycle shop, even though Strasbourg is on the French bank of the Rhine. I had to start my journey north without the guide and never did find one until I got to Karlsruhe, a distance of 113 km. It shouldn't have been that far, but lacking the guide I made some wrong turns.