Originally Posted by
CliffordK
Perhaps one of the more recent changes is the availability of wide and narrow tire sizes for any specific rim diameter. So, 26x1.5, BSD 559 may be a relatively new tire size for those wanting sportier tires for the MTB rims.
Skinny 26ers have been around for ages. This was one of my faves BITD:
Avocet Bike Tires - the Buyer's Guide, 2015
And yep, 650 B is generally used for 584 tires less than 48mm or so, with 27.5" generally reserved for wider tires. Similar to 700c vs 29".