I'm always learning new stuff that I probably should have known a long time ago. I always assumed that a 26" bike wheel, for example, was 26" in diameter. In fact, it's quite a bit smaller, and 26" is the nominal outer diameter of a typical tire (say 2") on a nominal 26" wheel. A 26" wheel is actually only 559 mm/22.0" in diameter. A 2" tire on that will take the O.D. out to 26". (Remember that the 2" tire has to be counted twice.)
So it was interesting to me to learn, while shopping for studded 29" winter tires to learn that 700 (mm) and 29" wheels have the same O.D. of 622 mm (approximately 24.5"). I thought 'no way' as 700 mm = 0.7 m = 0.7 x 39.37" = 27.56", which is way less than 29". BUT, once one considers that 700s are almost always skinny (typically 38 mm maximum), then the O.D. of a 622 mm wheel with a 38 mm tire would be 698 mm, where as a 622 mm wheel with a 2.2" tire would be 24.5" + 2*2.2" = 24.5" + 4.4" = 28.9". Aha!
Although 700 mm and 29" wheels have the same O.D. (without tires), the 700s tend to be skinnier (to accommodate smaller tires) and the 29s are wider (to accommodate larger tires). Live and learn.
Thanks again to Wikipedia:
https://en.wikipedia.org/wiki/Bicycle_wheel#26_inch_/_ISO_559_mm
So it was interesting to me to learn, while shopping for studded 29" winter tires to learn that 700 (mm) and 29" wheels have the same O.D. of 622 mm (approximately 24.5"). I thought 'no way' as 700 mm = 0.7 m = 0.7 x 39.37" = 27.56", which is way less than 29". BUT, once one considers that 700s are almost always skinny (typically 38 mm maximum), then the O.D. of a 622 mm wheel with a 38 mm tire would be 698 mm, where as a 622 mm wheel with a 2.2" tire would be 24.5" + 2*2.2" = 24.5" + 4.4" = 28.9". Aha!
Although 700 mm and 29" wheels have the same O.D. (without tires), the 700s tend to be skinnier (to accommodate smaller tires) and the 29s are wider (to accommodate larger tires). Live and learn.
Thanks again to Wikipedia:
https://en.wikipedia.org/wiki/Bicycle_wheel#26_inch_/_ISO_559_mm