32” (ISO 686) Wheels
If you pay attention to the goings-on within the bicycle industry, particularly the MTB side of things, you may have spotted some chat about a new wheel size. But before I dive into that, it might be worth just recapping where we are with bicycle wheel sizes as of right now. I’m not going to cover every single wheel size since the beginning of bicycle history, just the common sizes from the past 20-odd years, sizes you’re likely to have come across if you consider yourself a bike rider.
Let’s start with road bikes, at the beginning of my bike riding life, most road bikes had 27” wheels. This was close to the 700c size that most road bikes currently use. 27” was a popular size in the UK and the US but become pretty obsolete as the 700c designation that was common in Europe started to take over. The diameter of the 27” was actually a little bigger than 700c. There’s also a 650c size (not to be confused with 650b - see below) which is pretty rare but makes an appearance on some time-trial and tri bikes as well as race bikes for juveniles and smaller riders.
When mountain bikes got really popular in the 80s and 90s they all had 26” wheels, in the 2000s several manufacturers introduced the 29” wheel that most MTBs currently use. Interestingly the 29” wheel size is exactly the same size as the road 700c size. Fast forward a few years and we have an in-between size, 27.5” (also known as 650b). Not only is this popular in the mountain bike world, but has become pretty common on gravel bikes.
You might be a little confused at this point with the way we’re describing tyre sizes, you’ll have noticed that we’ve been mixing units and jumping around quite a bit. For tyres that are listed in inch sizes (eg 27”, 29”) these numbers refer to a very rough estimate of tyre diameter. Same with 700 or 650 except in this case it’s the tyre dimater in mm. The ‘c’ or ‘b’ suffix designates the width of the rim for that size of tyre. It’s not a number you can rely on but it is a convenient way of grouping tyres together.
Thankfully there are some standards that very accurately define tyre and wheel sizes and all current manufacturers adhere to these standards. The ISO wheel standard for bicycles describes a dimension that relates to the diameter of the rim where the bead of the tyre sits. Sometimes known as BSD (Bead Seat Diameter). An example of this would be ISO622 which is what all 700c and 29” rims/tyres fit into. Expanding on the ISO standards is the ERTRO standard. This takes the ISO dimension and adds a tyre width value. Like ISO, this is described in mm. An example of an ERTRO size would be 32-622 which is a 700c wheel with a 32mm tyre. I’ve added a chart at the bottom of this page that lists some common wheel sizes and their current standard designations. Check the sidewall of your tyre and you’ll see the ERTRO size.
So what does any of that have to do with 32” wheels? Well, the bicycle industry seems to have decided that a new bigger wheel size might be fun. And it seems like the 32” size (ISO 686) is the current favourite to make it onto production bikes. I should say here that 32” isn’t really a new size, it’s common in the unicycle world (along with 36” ISO 787). So there have always been tyres and rims available (well, about 2 tyre choices and about 1 rim!) and some small custom builders have been making use of these parts to build big-wheeled bikes for a while. There are a couple of companies specialising in building bikes for very tall people utilising 32” and 36” wheels in a small production environment but they are very much the exception.
With industry support, we’ll see more trye choices and more rim choices. This is already starting to happen. I have two different types of 32” tyres in stock right now (bicycle not unicycle), 1 type of carbon rim and 1 type of aluminium rim. I know of two rim manufacturers that have committed to stocking a 32” rim very soon. That trickle will turn into a stream very quickly.
This new wheel size is going to be interesting in a couple of different ways. The movement for this new size has been driven mostly from the mountain bike industry. Back in the 2000s we saw MTBs adopt the 29” (622) wheel size, effectively replacing the previous 26” (559) size. Proponents of this size argued that the bigger diameter meant the wheel rolled over obstacles better, smoothing out the ride and allowing faster speeds and more control. There wasn’t much argument against this, and 29ers became popular to the point where they are now pretty much standard. The downsides to a bigger wheel, a larger rotating mass, are that it’s harder to get the wheel up to speed, meaning a little slower acceleration, especially when pedalling out of corners, that sort of thing. There’s also the issue of the bigger rotating mass making it harder to change direction, kinda like a gyroscope always wanting to stay upright and stable. So quick changes of direction are harder. If the bigger wheel change (26 to 29) makes sense, then the logical argument is that a jump up in size again will have the same sort of benefits. I think this is true to some extent, the 32” wheel rolls over obstacles better and is especially beneficial on gravel bikes; the oversized wheel smooths out washboard-style gravel trails. But the downsides to the bigger wheel size will also be present and will be amplified. Getting those big wheels up to speed will take more effort, and on tight twisty trails, the bike will certainly feel harder to manoeuvre (everything else being the same). I think initially we’ll see people adopting a ‘mullet’ approach to the 32” wheel. The ‘mullet’ refers to a bike with two different wheel sizes, normally a bigger wheel in the front. The idea here is that you get the rollover benefits of the big front wheel to flatten the trail a little but you don’t have the downside of having to spin up a big wheel at the back. That approach is already popular with a lot of riders opting for a 29” front wheel and a 27.5” rear wheel. So the first way we’ll see 32” adoption is in the MTB world. The big wheel size will be chosen for performance and handling reasons.
The second way we’ll see widespread adoption of this size is to provide a better experience for big/tall riders. While it’s relatively easy to build a bike with contact points in the correct place for taller riders, the limitation of 700c (622) wheels means that often the rider feels like he’s stitting high up above the wheels, it can create an odd riding experience and there’s an argument that aesthetically it doesn’t look great. The two bikes you see below have exactly the same fit points, meaning the position the rider has on the bike is the same, from a comfort point of view there’s little difference. But it’s not difficult to see what bike looks ‘right’.
The fit and riding position of both of these bikes is identical. The bike on the left has 700c wheels, the bike on the right has 32” wheels.
I’m excited to see more components (tyres, rims) become available for 32” wheels, I think this is going to be transformative for bigger riders who have traditionally had to opt for the biggest production size available and then try to tweak it to work. We’ll be able to design bikes that have the rider sitting between the wheel rather than high up on top of the wheels.
So if you’re either an MTB or gravel rider looking to explore this new wheel size or a taller rider looking for something that fits and rides better, get in touch and we can talk about what we can do for you. If you’re a framebuilder and want to dip your toe into the water, building big-wheel bikes then I can help out with the supply of rims, tyres and spokes that I keep in stock here. Getting hold of these parts still isn’t too easy without committing to big quantities.
