A Very Brief Explanation of Bicycle Tire Nomenclature

Gary Fisher at Sela Marathon, CZ (from mtbs.cz)

There’s a lot of chatter about which is the more valid or perhaps the more marketable label for 650B MTB wheels/tires. There’s a push by many to call it 27.5” so that it’s easier for the average consumer to understand that it is a “new” size between traditional 26” mtb and the “new”-ish 29er. From my sarcastic quotation marks, readers should take that I think most of the arguments are stupid. I’m still a little peeved that I had to deal with about 5 years of uninformed observers and (even more maddening) smug dipshit bike shop employees swearing that 29er was an entirely new and separate standard from 700C. The term Twenty-Niner came to be because it rolls off the tongue with ease, becoming its own marketing slogan. It worked in that everyone knew we weren’t talking 26-inch mtb anymore. Yet to ditch the more common, French 650B designation for 27.5” is a fail. Six-fifty-Bee has the same number of syllables as Twenty-Niner, so let’s just leave it there. What? Are we gonna be saying twenty-seven-point-fiver? That’s ridiculous.

Historically, just about all the common tire designations originally described the outer diameter of the tread for specific width tires. Of course if the tire was something different than the typical width, then the diameter would be different as well. The French designations 650, 650A, 650B, and 650C were all supposed to be 650mm in diameter at the tread for the tires they were originally meant to have. 700C is actually 700mm if the tire is about 35mm wide (initially the standard width when 700C was first introduced). But now we find ourselves in a situation where 650 & 650A (ISO 597 & 590mm respectively) have all but vanished, 650B (ISO 584mm) reemerged from the same oblivion but has swollen to 55mm widths, and 650C (ISO 571mm) has shrunken to 20-23mm tires for triathletes and junior road bikes. Likewise, 700C is 736mm with a 29er tire mounted on. Generally all the French tires designations have an English name for the exact same ISO measurement, so 650B was also known as 26 x 1-1/2” by the British. Tire standards outside this Anglo-French alliance, like mtb 26” (ISO 559), can be blamed on American industrialists, particularly Schwinn.

Going back to what to call mtb 650B, it has already been called 26”x1-1/2”, so now calling it 27.5” just needlessly complicates things. Okay, fine, “29er” sounds good, and historically there weren’t bigass 700C tires before Willits et al pushed for them in the mid-/late-90s, so calling it 29er isn’t overlapping onto some other nomenclature’s range.

When the 29er revolution was still gathering momentum, the name 29er helped to conceptually differentiate these bikes from hybrids and road bikes, while also defining 29ers as a new (and implicitly better) alternative to 26” mountainbikes. But it’s not like uninitiated consumers are going to confuse MTB 650B with older genres of bikes that use the same rim standard (eg esoteric French touring bikes), because only hardcore bike nerds even know they exist. And arguing that we should call it 27.5” because consumers won’t understand how 650B relates to 26” and 29er is assuming that those consumers are pretty f***ing stupid yet surprisingly savvy with physics. Rather, you’re gonna market an intermediate size wheel…..based on it being a compromise of rolling resistance, inertia, and its dimensions within a complex linkage rear suspension…. to a consumer who is incapable of keeping track of a whole 3 wheel choices for today’s mountain bike market?

-How big is a 26-inch wheel?

-About 26 inches.

-How big do the wheels get?

-Well, there’s a 29er.

-How big is that?

-29 inches.

-Sweet. Are there anymore choices?

-Yeah, there’s one more called 650B. Funny story about why it’s called that, but all you need to know now is that it’s right between 26-inch and 29er.

-I cannot comprehend that a wheel could be between 26” and 29” in diameter. Please show me some line graphs and performance studies instead.

Everyone knows the story of Goldilocks and the three bears, but no one cares exactly whose stuff Goldilocks preferred. The point is that she picked the one that wasn’t too much nor two little; she picked the middle one. That’s how 650B marketing will work on the consumer, not by step-by-step recreating a “29er Revolution 2.0”.