Whats the deal with wheel size?

650b? 29er? 27 1/4? 622-28? Plus size? Whats the deal ?

The world of bikes is awash with different wheel sizes, and the sadly-passed statesman of cycles, Sheldon Brown, has amassed a long list of the different wheel sizes and their respective histories. However for you and me, we just want to know the tyre sizes, the wheel size, and ultimately what they’re good for!

First, a little bit about naming

There are many different ways of naming the same wheel size. For example 700c can also be known as 28-inch but the rim is the same as a 29-inch (29er) mountain bike. What the?

Part of the reason for this comes from where the rim or wheel size was first popularised. Mountain biking started in the USA, where they tend to measure wheel diameter in inches. The original mountain bike wheel was 26-inches. But as great innovators of bike tech mountain-bikers are, they were really the first to use a variety of sizes. One of the sizes they adopted was a standard road 700c wheel size, but they called it a 29-inch (or 29er) wheel because that’s what the outside diameter measures when you put a mountain bike tyre on it. On the flip-side, road cyclists adopting the mountain bike standard of 27.5-inch gave us what we generally know as 650b.  Of course, all of these rim sizes existed previously, but their recent adoption in different contexts have given them different naming.

There’s good news and bad news in dealing with this confusion of naming. Firstly there is a standard that everyone can get their head around called the ETRTO (European Tire and Rim Technical Organization) or ISO (International Organisation for Standardisation). The ETRTO or ISO gives us the diameter of the rim in millimeters.  To figure out the ISO our man Sheldon gives us this lovely bit of guidance

“The ISO system uses two numbers. The first is width in millimeters. For the rim, this is the inner width between the flanges, as shown in the diagram; for the tire, it is the inflated width. This will vary a bit depending on the width of the rim.

The second ISO number is the critical one: it is the diameter of the bead seat of the rim, in mm (“B.S.D.”). Generally, if this number matches, the tire involved will fit onto the rim; if it doesn’t match, the tire won’t fit.”

In short, a wheelsize of 25-622 is the classic road bike 700c with a 25mm tyre, and a 57-559 is a retro mountain bike 26 inch by 2.125 inches. However the bad news is, everyone, road bikers and mountain bikers, are set in their own ways and you’ll probably have to learn the jargon about the three main sizes, but at least its only three!

So here is a list of the three main wheel sizes that you will find on adult push bikes today, their uses, strengths what the’re called and some notes on sizing, plus a few honorable mentions.

26-inch  (I.S.O 559)

  • Old Mountain Bikes
  • Touring Bikes
  • Mountain Bikes for shorter people
  • Some city bikes

The 26-inch wheel size comes from the original mountain bikes. Early mountain bikers found that this smaller wheel size made handling more responsive and allowed for better riding on the trails. Today they are still found on entry level mountain bikes, and kids mountain bikes. The other big use is on touring bikes. The theory behind this is that 26 inch parts are more widely available worldwide than then newer standard of 700c. However this advantage is decreasing day by day.

The smaller wheel however allows for the manufacturers to build the ideal frame geometry for smaller riders. With a bigger wheel, builders make compromises on head angles, standover, slackness etc. This decreases the intended performance of the bike, so the 26 inch allows them to build the desired ride around the smaller wheel. Some manufacturers like Surly make small sizes of some of their flagship bikes such as the Disc Trucker in 26-inch only, due to the aforementioned reasons. Furthermore, the smaller wheel is stronger, ideal for touring under load. The other advantage of a 26 inch is that it accelerates quicker than a bigger wheel, making it nimble for city riding, however the rolling efficiency of the wheel pales in comparison to its bigger brothers.

  • Commonly available worldwide
  • Cheap parts
  • Stronger wheels
  • Good acceleration
  • Good for us shorties
  • Nimble
  • Less rolling efficiency than larger wheels
  • Outdated, which may lead to restriction in tyre choice
  • There are a number of different 26″ sizes, used on vintage bikes, which differ from the modern 26″. Again, refer to the ETRTO/ISO number to be sure.

 700c or 29er (I.S.O  622)

  • Modern road and mountain bikes

The standard size, and for good reason. It’s the most ‘efficient’ wheel size meaning for the amount of effort you put it, you’ll go the furthest—a handy feature for push bikes! It’s found on most commuter bikes, road bikes, and cyclocross bikes, plus many mountain bikes. There’s not much to really say about the wheel size apart from the fact that if you ride bikes chances are you will have some dealing with it. Smaller wheel sizes can accelerate quicker, and can be more nimble, but lets be honest speed is king, and when you’re riding 700c you’ll go the fastest. When mountain bikers first adopted the larger 700c as a wheelsize (what they called a 29-inch), they broke a lot of wheels, but as wheel-building technology gets better this has greatly reduced.

700c is the easiest wheel size to get tubes and tyres for in Australia. Generally the only time you wont be dealing with 700c is if you’re rather short and are better suited to a smaller wheel size, or if you’re riding touring bikes or mountain bikes.

To get the right tubes and tyres, refer to the width of the tyre, which will be either in mm ( 23, 32 etc.) or inches for mountain bikes (2.0, 2.4 etc).

  • Most Efficient
  • Fastest Rolling
  • Widely available
  • slower acceleration
  • can affect bike geo’s for smaller riders
  • Longer spokes = less strong wheels

27.5-inch or 650b (I.S.O 584)

  • Mountain Bikes
  • Road “Plus”

27.5-inch came about when the new 29ers were coming into a lot of problems—i.e broken wheels. So the brains trust in america knocked out something in between. 27.5 as a wheel size gave you the best of both worlds: the fast rolling of a 29er, but the nimbleness and strength of a 26er. Many mountain bikes are spec’d with this wheel size for this exact reason. It works especially well if the rider is shorter, and many manufactures spec’ wheel size of mountain bikes according to the size of the rider.

WTB Byway Road Plus Tyre

Recently, road cyclists foraying into gravel riding have started using 650b “road-plus” wheels. The idea behind this is that the outer diameter of the wheel / tyre combo of a 650b wheel with a 47mm tyre is the same as a 700c wheel with 28-32mm tyre. This gives you much more “cushion’ when you’re pushin'” but as the outer diameter is the same, you’ll roll roughly at the same speed and efficiency. It also allows for a bigger tyre in a frame that otherwise wouldn’t be able to clear it.  ( We’ve done some builds that have this idea in mind ) This is still a new section of the bike market so parts aren’t very widely available yet but its becoming more so. However WTB are the trailblazers and we stock their lovely Horizons and new Byway tyres in a 47c.

  • Best of both worlds (fast-rolling and nimble)
  • Good for shorties
  • more comfort and grip for road bikes
  • Not as common
  • Jack of all trades, master of none…

Honorable mentions

27 x 1 1/4

Old commuter standard, still found on a lot of retro bikes. Basic parts still widely available, but no bikes are being built with this size anymore.

Plus Size

Plus basically means ‘bigger’. Again coming from the idea that more tyre volume gives you more comfort, more grip, and more confidence, mountain bikes have in the last few years had a big push towards ‘plus’ size wheels. While the BSD and ISO will be the same on their respective wheelsize (29+, has the same as 29er), the rims will be wider to accommodated the larger tyre volume. Plus size is becoming all the rage, so expect to see much more of it.



5 Second Summary

  • 3 most common sizes are 26 inch, 27.5 inch (or 650B) and 29 inch (or 700c)
  • All have strengths and weaknesses
  • Mountain bikers use inches, road cyclist use milimetres
  • ETRTO or ISO will give you wheel size based on the tyre.