Ride, Wrench, Swap, Race
Join Date: Jan 2010
Location: Northern California
Posts: 9,194
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
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As far as actual width is concerned, it's not so much what is printed on the sidewall but what the actual inflated width is on any particular rim.
Those old Expedition tires were no bigger than a 1-1/4" Pasela, or 1-1/4" World Tour, or 1-3/8" folding Hi-Lite Tour, all are about 32mm upon initial inflation.
Some 1-3/8" tires such as Kenda Cross-Cyclo, Club Roost or Cheng Shin actually measure less than 32mm, more like 30mm, but still are wider than most tires marked 1-1/4" since these can be as narrow as 27mm on a 22mm rim!
Like a lot of poorly-standardized bicycle parts, such as bottom bracket spindles and even quill stem extension lengths, it is up to the end user to actually measure (and perhaps even test-install and/or test-ride) things if they want to achieve precise results relating to things like crank chainline, bike/rider fit and tire clearance.