There are a couple of wheel/tires sizes that are standard on American Bicycles. Bicycle tire sizes are normally measured on the outside of the tire and this is called the nominal tire size. For example a 26 x 2.0 tire will fit on a 26 x 1.75 or 26 x 1.5 wheel. The approximate outside diameter with the tire installed is 26 inches.
What is the difference between 26 x1.75 and 26 x 1 3/4?
The 1 3/4 size is actually a different bead size so the tires will not interchange. The 26 x1 3/4 is an old Schwinn size that has not been made since the 60′s but the tires are still available to fit these rims.
Is 27″ the same as 700c?
No the 27 x 1 1/4 tire will not fit a 700c rim. The bead of the tire is about 1/2″ too big. Tubes will normally work on either 700c or 27″ tires just fine.
Is 29″ the same as 700c?
Yes, the bead size of a 29″ mountain bike wheel is the same size as the bead size of a 700c rim. Normally the mountain rims are a little bit wider to allow the 29″ tire to fit a little better.
Old 3 speed bicycle sizes
The old 26 x 1 3/8 tire size is not the same as the 26 x 1.75 or the 26 x 1 3/4. There is also another 26 x 1 3/8 tire size that was made by Schwinn until the late 70s that was called 26 x 1 3/8 or 26 x 1 1/4. The bead of this rim is just large enough that it seems you will be able to get the regular 26 x 1 3/8 tire on. You will ruin the tire if you do get it on and it is nearly impossible to get back off.
Rick Kern Bicycle Hangar Missoula, Mt