Some parts of cycling tech can be particularly confusing. One such area in which this is particularly apparent is mountain bike wheel sizes.
Cycling is a sport that has rapidly developed over the past few decades, with new disciplines cropping up and adding new types of tech along with different names for already existing tech and sizing.
In the case of sizing, this usually happens as the result of new disciplines forming in places that use a different measurement system. Sizing is something that has a surprising effect on your ride, especially when it comes to wheel sizing.
Wheel sizing is an extremely confusing part of cycling, especially if you happen to take part in multiple disciplines. This is because there are multiple accepted sizing scales and conventions associated with different disciplines that are actually the same.
So, what difference does mountain bike wheel size actually make to your ride? And what are all of the different wheel size scales?
Don’t worry! In this guide, we’ll help you navigate the complicated world of bike wheel sizes with the help of a mountain bike wheel size chart to easily convert between the different scales. In this article, we’ll be covering:
- Mountain Bike Wheel Sizes Explained
- How Does Choice Of Wheel Size Affect Your Ride?
- French Wheel Sizes Explained
- ISO Wheel Sizes Explained
- Mountain Bike Wheel Size Chart
Let’s dive in!
Mountain Bike Wheel Sizes Explained
Mountain bike wheel sizes are the measured diameter of a wheel, including the tire, measured in inches.
For example, a 29″ mountain bike wheel does exactly what it says on the tin: it measures to be (roughly) 29″ in diameter, including the tire.
How does your choice of wheel size affect your ride?
The most common mountain bike wheel sizes are 26″, 27.5″, and 29″.
These days, the most popular mid-range to pro-quality mountain bikes tend to be 29″ for several reasons, but they’re not for everyone.
When mountain bikes were first developed, 26″ wheels were used. However, just like many other things in cycling, it was soon realized that there might be more advantages to using a bigger wheel.
So, 29″ wheels became the most popular size, and still are. But this may be starting to change, with many beginning to opt for the happy-medium size of 27.5″.
So, which size is best?
Well, there’s no way to definitively answer this question since different riders will prioritize different things on the bike. But let’s go through some of the advantages and disadvantages of each of the most common sizes.
26″ Mountain Bike Wheels
If you’re in the market for a new mountain bike, it’s unlikely you’re going to come across many equipped with 26″ wheels.
This is because they have slowly been phased out of the MTB world, with more and more people opting for larger wheels.
In general, 26″ mountain bike wheels will feel less stable, more agile, and bumpier than larger sizes.
This is because the smaller wheel size has less rollover capacity – meaning that it won’t be able to roll over large obstacles quite as easily, resulting in a more bumpy feeling.
The advantage, however, is that smaller wheels are lighter since they use less material. A lighter wheel will accelerate faster with the same force applied to the pedals and, by extension, will decelerate more easily, increasing the brakes’ effectiveness.
29″ Mountain Bike Wheels
After a bit of a false start in the mountain bike wheel market, 29″ wheels soon took off and have now become commonplace on many mid-range to high-end mountain bikes.
So, they must be better in every way than 26″ wheels, right?
Well, no. Just like anything else in cycling, there are advantages and disadvantages to each wheel size; it’s just that many deem the advantages of ’29ers’ to outweigh those of 26s.
As previously discussed, 29″ wheels will have a more sluggish feel to them than 26″ wheels. The increased weight will result in slower acceleration and deceleration, making tight-course handling considerably more clunky and slow.
This is a particular disadvantage if you need to avoid rapid-fire obstacles or traverse tight corners regularly.
Luckily, 29ers come with a set of advantages that could be considered to somewhat offset the disadvantages. The first of these is the previously mentioned increased rollover.
This means that you’ll more easily absorb small obstacles on the trail, and perhaps more importantly, you’ll be able to get over larger ones.
At extremely high speeds, for example, during a downhill MTB race, any small bumps in the trail are going to make you feel extremely unstable and unsafe if you’re using wheels that are too small.
So, using a large wheel helps you to feel more stable and comfortable at high speeds.
27.5″ mountain Bike Wheels
27.5s were more recently introduced to the MTB world to create a sort of “happy medium” between the two.
27.5s are faster to accelerate and decelerate than 29ers, but more sluggish than 26″ wheels.
They’re also less able to absorb obstacles and bumpiness in the trail than 29ers, but more able than 26″ wheels. However, since this difference isn’t quite as significant as that of 29-26″ wheels, many still choose 27.5s for increased agility.
- Unsure whether 27.5s or 29ers are better for you? Check out 27.5″ Vs 29″ Mountain Bikes: Which Should You Choose?
French Wheel Sizes Explained
These are measured as the rough diameter of the wheel, including the tire, in the same way as mountain bike wheel sizes, except using millimeters.
For example, a 700c bike wheel means that the wheel measures 700 mm, including the tire, across the diameter.
The thing that makes sizing so confusing, however, is that the rim of a 700c wheel – excluding the tire – is the exact same diameter as a 29″ mountain bike wheel!
Another common road and gravel bike wheel size, 650b, is equivalent to 27.5″ wheel mountain bike wheels and is said to measure 650 mm across the diameter, including the tire.
- Attempting to choose between 650b and 700c wheels for your gravel bike? Take a look at our article 650b Vs 700c Wheels: Which Should I Choose?
Those with off-the-charts mental math skills may be up in arms at this point since, upsettingly, 29″ is actually 736 mm, and 27.5″ is 698 mm. This discrepancy is hard to explain, but trust us, these wheels are the same size.
One of the most likely explanations for this discrepancy is that measurements that include the tire are only ever going to be a rough guide since tires of different volumes will radially protrude to differing degrees.
Additionally, mountain bike wheels will use wider tires with a larger volume than road or gravel bike tires.
So, the same-sized rims are likely to measure in at a larger diameter when including the tire since the tires will add more to the diameter of the wheel if their volume is larger.
Regardless of if there is some logic to be found in the mismatch, it’s still frustrating to have such an inconsistent conversion between sizes.
So, that’s why there is yet another wheel sizing system: ISO sizing.
iSO Wheel Sizes Explained
The prospect of an additional sizing scale is probably not something you feel will make understanding these sizes easier. However, in this case, it actually might!
The reason for this is that ISO wheel sizes attempt to solve the inconsistency problem with the other two measurements.
That is, if you define a sizing scale of a wheel as inclusive of the tire, then it’s completely impossible for that size to be exactly accurate when comparing the same wheel with different volume tires.
That’s where ISO sizing comes in. Clearly, the most logical thing to do would be to measure the wheel to the edge of the rims – not including the tire – so that the sizes remain consistent between disciplines.
So, that’s exactly what ISO sizing is. The ISO size of a wheel is the measurement, in mm, of the diameter of the wheel between the rim beds.
For example, a 700c (or 29″) wheel works out to have an ISO size of 622 mm, and a 27.5″ wheel (or 650b), has an ISO size of 584 mm.
Mountain bike wheel size chart
If there’s one thing that’s clear about all of these measuring systems – it’s that it’s confusing, haphazard, and upsetting to measure wheels in different wheels and quote their sizes in different units.
So, in order to help you out here, we’ve made a mountain bike wheel size chart so that you can convert between French, ISO, and MTB wheel sizes with ease!
Disclaimer: A note on tire width
Although wheel sizing systems refer to wheel size inclusive of the tire (except ISO standard), remember that the written wheel size only represents a size difference between the wheels themselves, excluding the tire.
In other words, two 29″ mountain bike wheels with different-sized tires fitted could be sat next to each other. The one with the bigger, wider tires will have a greater total diameter including the tires, even though the rims themselves are exactly the same size – 622 mm.
29″ simply refers to the rough total diameter you would expect a 622 mm wheel to have with a typical mountain bike tire fitted.
If this sounds confusing, that’s because it is – and it’s why the ISO system was introduced.
If you want to check what the actual comparison of two different mountain bike wheel sizes, including the tires, is, then check out this excellent resource.