Double-checked this morning and it is 27.2. I don't know much about different tubesets, but perhaps 26.6 is correct for the Tenax tubeset used on the Voyageur, but incorrect for the SP/SLX tubset on the Voyageur SP. Both the 1984 and 1985 catalogs show 26.6 for both variants..
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72 Fuji Finest 72+76 Super Course, 72 Gitane Tour de France, 74 P-10 & 79 Tandem Paramounts, 76 Grand Jubile,84 Raleigh Alyeska, 84 Voyageur SP, 85 Miyata Sport 10 mixte 89 Cannondale ST400 and a queue