My recently purchased early 70's Lejeune tandem came with original Campy Tipo hubs laced to what I thought were Araya 650B rims, but with the oddball 650D (xx-587) tires made only by/for GT. As 650D wheels could not possibly have been original, I figured someone had substituted incorrect 650D tires for the proper 650B (xx-584), but got away with it because the difference is only 3mm. I purchased some 650B Michelin World Tour tires and installed one today. It went on, but only with great effort. The rim is marked Araya RM-20, but has no size markings. I measure it about 570mm inside diameter and about 597mm OD to the tops of the flanges, but I don't think I can measure a built-up rim closely enough to tell the 3mm difference between 650B and 650D. It is an ominous sign that my most recent Sutherland's lists an Araya RM-20 among 650D rims, but another Araya model as 650B. Can anyone confirm that the RM-20 was made in 650D only, or suggest a more foolproof method of distinguishing a 650B from 650D rim? I'm beginning to think that someone took the insane step of rebuilding the wheels with 650D rims, though I suppose at the time one might have thought that GT would succeed in making 650D a standard. I see no point trying to find spare 650D tires, and if I conclude the rims are 650D, will rebuild with 650B, both because that is original and because 650D tires are essentially impossible to find. Anyone have some different advise? Meanwhile, anyone see any reason other than difficult tire changes that I shouldn't use the 650B Michelins on the possible 650D rims?
Jerry "and you thought 27" tires were becoming a problem" Moos