700 vs. 29" bike tires

[Number_35]

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

 

[ragtoplvr]

That probably lets the Chinese use the same lacing machines they already had.

Google wheel lacing the video is good

 

[NYEngineer]

Originally Posted by ragtoplvr
That probably lets the Chinese use the same lacing machines they already had.

Google wheel lacing the video is good



Yep. That's almost exactly how it came to be.

This works to my advantage because I'm building a set of 700c wheels for my Surly Krampus for street tires. Quick swapping.

 

[CR94]

Originally Posted by Number_35
... 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).
It's even more complicated than you think, due to the long, convoluted, and illogical history behind size designations. The 559 mm [22"] and 622 mm [24½"] dimensions you mention are two of the numerous bead circle diameters (BCDs) of bike tires. Obviously, the bead diameter must be a little smaller than the overall diameter of the rim. Confusingly, there have been at least four different (incompatible) diameter wheels nominally called 26 inch. My old Schwinn, for example, takes 26×1¾" tires (not to be confused with 26×1.75", which requires a different rim) on 571mm [22½"] BCD rims.

Early in bike history, sizes were listed as a TIRE diameter in millimeters and a letter to designate width. That system required a different rim diameter for each width of a given tire diameter, which required an unwieldy large variety of rim diameters. One common size was 700mm in "C" width (about the size of a modern 38mm tire), which required a 622 mm BCD rim. It was decided to standardize on that diameter rim, even for narrower tires. Thus, today most road tires are called 700c, even though most of them are narrower than the original 700c, and nothing about the tire or rim is as large as 700 mm. The 27" size that was common in the 1960s through about mid-80s requires a 630mm BCD wheel---close to the now-standard 622mm, but incompatible.

 

[DdDd]

Yep, 29ers were originally just wider tires on laced up 700c road bike rims. You gotta work with what you have when prototyping. After it caught on the tires became wider still and the rims more stout.

Interestingly enough diamondback bikes did the first 29er mountain bike in the mid eighties. They weren't clever enough to call it that or market the strengths of easier rolling wheels. Never caught on, but eventually was "rediscovered" by some enthusiasts who were looking for the next big thing.

 

[Number_35]

CR94, thanks for the history lesson! I find this stuff really interesting. I wondered where the C in 700C came from.

I get how different inventors acting independently come up with creative solutions, and that the market then more or less sorts out which ones are good and which ones are not, but sometimes I yearn for more standardization. How many ancient bottom bracket tools do I have?