Wheel Size Wars

Everyone should ride 700c wheels…”

“Everyone knows that 650c wheels are more aerodynamic!”

“My 29-inch mountain bike is totally better than 26-inch on the local trails…”

I could go on. There seem to be a million and one arguments either for or against each wheel size. How many do we need? Is one enough? What about two? If you read mountain bike news, you may have heard that they’ve recently (re)introduced a third wheel size.

Above image © Trek

It’s a complicated topic. Some may even say it’s personal. What to do? Let’s see if we can’t take a step back and look at things from a - gasp! - reasonable point of view.

What do wheel sizes mean?

You may have noticed that the way we talk about wheel sizes sounds confusing. Mountain bikers all used to ride 26” wheels. That’s similar in diameter – but not the same as – a triathlete’s 650c wheel (however, some people mistakenly refer to 650c wheels as ’26 inch’ – adding to the confusion). The interesting part that many people miss is that these names are actually in reference to the outside tire diameter, not the wheel (650 refers to the diameter in millimeters). This, of course, assumes that there is only one available tire diameter per wheel diameter, which is not the case. Clearly, the names are just an approximation. What’s the take home? Wheel size names don’t actually mean anything, so it’s high time we all start getting over it.

For the sake of simplicity, I will lay out the most common modern wheel size names and what they intend to denote:

700c: The ‘normal’ size for road wheels. To make things extra strange, there are a few nicknames that are either completely incorrect or do not mean anything: ‘27 inch’, ‘28 inch’, and mountain bikers call them ‘29ers’. Confused? Me too. Real 27 inch wheels and tires can still be found, but are generally only featured on older bikes (and do not fit on ‘700c’ rims).

650c: The smaller size for road and triathlon wheels.

26”: The smaller size for mountain bike wheels (and, until recently, it was the only size readily available).

29”: The larger size for mountain bike wheels. The big secret? These are just 700c rims laced to mountain bike hubs.

27.5” or 650b: The new ‘tweener’ size for mountain bike wheels. This is the size for true connoisseurs, for whom 26” is a touch too small, and well – 29” would just be excessive.

That may seem like a lot of wheel and tire diameters. Over the course of history, there have actually been many more sizes. This is a partial list from the late and great Sheldon Brown:

That’s only some of them.

To really understand this mess, we need to look at the second column on Sheldon’s spreadsheet (above). It says ISO (short for International Organization for Standardization). We’ve written about the ISO method of tire naming in the past, although under its former name of E.T.R.T.O. (European Tyre and Rim Technical Organization). This system uses two numbers. The first number is the tire width in millimeters (i.e. 23). The second number denotes the wheel and tire’s bead seat diameter, seen as dimension A in the graphic below:

Above image © Schwalbe tires

In the case of a 700c wheel, the bead seat diameter is actually 622mm. So, the real name for a 700x23mm tire is 23-622. That leaves no guessing, no ambiguity, and no chance for matching an incompatible tire and wheel. A 29-inch mountain bike tire might be 56-622. A cyclocross tire could be 32-622. Most tires list this ISO size right on the sidewall.

ISO sizes of common wheel diameters

Now that we understand ISO sizing, let’s look at how the common rim diameters actually stack up.

Why are we listing both road-intended product and mountain-intended product? Isn’t this a triathlon publication?

I’m including mountain product because I want to make a big stink. It’s about time somebody did, so it may as well be us. 26-inch mountain bike wheels are just fine. 29-inch wheels are great, too. Similar to 650c and 700c in triathlon, the size of wheel your bike comes with ought to be based on that bike’s size – which corresponds to the rider’s physical dimensions of height, inseam, and so on. Where the two sizes meet, there is some gray area. If you stand five foot, seven inches tall, you could very likely do fine on either a 650c or 700c triathlon bike. If you’re five foot, nine inches tall (or thereabouts), you could really make a case for either a 26 or 29-inch mountain bike. Now, don’t think we’re forgetting that there are some special situations and applications in which one wheel size tends to be chosen by riders of ALL heights (for example, downhill racing – which is done almost exclusively on smaller 26” wheels due to limitations of suspension geometry and clearance). Those special situations stand, and we’re not messing with them.

With the previous paragraph in mind, there are a few things that are bugging me:

1. The (very) new idea that 29-inch mountain bike wheels are somehow better for ALL riders (especially for cross-country style racing). Some companies are going so far as to discontinue 26-inch wheels altogether. If you’re five foot, two inches tall, and want to buy a mountain bike from one of these companies, I say: Good luck. Similar to the problem of too-short riders on 700c triathlon bikes, you often cannot even achieve your proper fit coordinates (namely, getting your handlebars low enough). Of course, there are some work-arounds popping up to ‘make it work’ – negative rise bars, super short-stack headsets, and the like.

2. The now-tiresome idea that 650c wheels are unnecessary for anything. We have little left to say on this topic. They most definitely have a purpose and place in road and time trial applications. Our friends at Cervelo recently published this well-rounded piece:


3. The idea that, of course, a third wheel size for mountain bikes (650b) is absolutely necessary, and it’s totally worth the increase in SKUs for manufacturers, increase in inventory for dealers, and increase in confusion for consumers. The author apologizes if his sarcasm has gotten a little bit out of hand at this point.

A New Idea… or ‘The Stink Gets Stinkier’

An idea sprouted – as many do – in the depths of our reader forum. I was discussing the ins and outs of wheel sizes with engineer and uber-cycling-geek, Tom Anhalt, and Greg of Dark Speed Works, a manufacturer of triathlon accessories. Greg had a wonderful idea: Why not use 650c and 700c for all major disciplines of cycling – road, triathlon, cyclocross, track, and mountain bike? Why not use those two, and ditch everything else?

Couldn’t these two rim diameters satisfy everyone, limit inventory for dealers, and limit multiple SKUs and cost for manufacturers? Looking at our ISO chart above, we can see that 650c splits the difference between mountain biking’s 26” and 650b. Surely a 650c rim diameter could satisfy both needs – along with the needs of road cycling and triathlon. If you look at the Cervelo article (linked above), you see how small the differences in angle-of-attack really are, especially when we’re looking at three rim diameters for a given application.

Above image © Cervelo

Tom commented:

“Yeah, it's too bad that the MTB industry had to jump on the whole 650B thing right off the bat. I guess they were too afraid to ‘miss the boat’ like some of them did with 29ers. If someone had taken a step back and realized what was talked about yesterday (i.e. just ‘upgrade’ the 26-inch wheels to 650C), it sure would have been a lot easier to accomplish.

The ironic thing I find about the whole wheel debate, especially in the MTB world, is that nobody seems to take into account the effect of tire size on the whole issue. Do you know that the outside diameter of a 26-inch wheel with a 2.1 knobby tire is about the same as a 700C wheel with a 23C road tire (within 3-4mm radially)? It cracked me up when 29er advocates would say, 'You ride bigger wheels on the road, why are they so small for off-road?' They didn't realize that they were actually riding basically the same sizes if you account for the tires. Hell, you can probably change your effective wheel diameter more just by changing tire sizes, than the ~.75 inch radial difference between the 3 MTB wheel sizes.”

We both realize that we’re thinking pie-in-the-sky at this point. We don’t expect the industry to turn around now. We just couldn’t help but think of the possibilities…

-A decrease in the number of diameters (from four to two) means that our options in rims would multiply. With road rims going wide nowadays, what would keep a manufacturer from using the same mold for both road and mountain applications – and only change the carbon layup? Can you say a-LOT-more carbon clincher, tubular, and tubeless options for both road AND mountain?

-The potential in tires… I’m talking the full gamut of narrow, wide, knobby, slick, and everything in-between. How about a legitimate 28c training tire for a 650c road bike? Or perhaps some more tubular options for mountain bike racing? With only two diameters to worry about, the possibilities are enormous. Oh yeah – let’s not forget about 650c latex inner tubes.

-The long-term cost savings for all points in the supply chain. Money saved from reduced inventory could be put towards, well, anything else.

How would we decide what size bikes get which wheel size? As previously mentioned, there is and will always be some grey area for ‘average size’ riders. Manufacturers would have to figure this out on their own. What we need to stop is this nonsense of absolutes. XC mountain biking is ALWAYS better on XYZ wheel size. Road bikes should ONLY use 700c wheels. We suggest – barring the special situations previously mentioned – the scaling should be done by rider size, regardless of application. The only true ‘absolute’ is that it will always be easier to fit a large rider on a small wheel than a small rider on a large wheel.

There is a single reality of business that causes the industry to continue this silly debate about wheel sizes, and that is inventory. We want to sell new features – new wheel sizes – but we don’t want to deal with the inventory of keeping up all of the options. 700c can ‘work’ for any road application, so kill 650c. 29-inch was hated-then-loved, so some manufacturers are killing their 26-inch bikes. Now 650b comes walking in, and all-of-a-sudden it’s legitimate? Instead of doddling around, killing some wheel sizes and resurrecting others, why don’t we just make life simple? With our fantasy solution, you fix the inventory problem AND you fix the fit problem for both road and mountain – all at the same time! Does it sound too good to be true? It isn’t!

Clearly, Tom and I are a couple of nerds who think about this stuff too much. Forgive us, if you can. We hope our sentiment can be seen for what it really is – which is to say – optimistic and well-intentioned. It’s unfortunate to see the industry make some very smart choices in some areas based on sound reasoning, and such poor choices in other areas (based on poor reasoning, fashion, or something else entirely). As Tom said, nearly causing me to spit out my morning coffee, “Sometimes the cognitive dissonance is deafening.” Amen, Sir.