Step into any bike shop and you’re bound to see a range of tires on display – and a ton of numbers to go with them. Whether you’re looking to upgrade your wheels or need to swap a tube fast, it’s important to understand what all of these mean so you don’t end up with a flat (or worse).
We’ll go over all of these different tire measurements and how some manufacturers are trying to help standardize the process (while adding even more numbers in the meantime).
What Do the Different Tire Sizes Mean?
The first number in a tire listing refers to the diameter of the bike tire while the second number is for the tire’s width. Tires are typically measured in millimeters, which we’ll explore later on in the article.
First, a bit of history. We generally use the French system of sizing bike tires. They categorized bikes in three different widths, from smallest to largest: a, b, and c. The latter is what most tires today are classified as, so you’ll usually see a “c” at the end of any bike tire size. It’s not really necessary because “a” and “b” are all but obsolete these days, but the tradition remains. (Source.)
For more on this, we highly recommend that you check out our post ” Does Road / Triathlon Bike Tires Size Really Matter ?!“
Now let’s dive into the differences in sizes and what that means for your next ride.
What Does 700x32c Mean?
700x32c tires are approximately 700mm in diameter and 32mm in width. Translated to inches, you’re looking at roughly 27 ½ inches by 1 ¼ inch. However, these are considered nominal measurements, meaning they’re a close estimate rather than an exact number.
There are a lot of factors that can change the ultimate size of a bike tire including how it sits on the rims, the tire pressure, tread, and even minor manufacturing issues. If you were to take a ruler out and measure the exact size, you’re likely to be a little under or over 700mm. The width will also vary a bit, especially if you change the pressure of your tires.
That being said, the nominal measurement shouldn’t impact whether or not a tire fits your wheel. If you have a bike that comes with 700x32c tires, then you can be comfortable getting new tires that are the same size, even if they’re a different brand.
You can play around with different sizing depending on the tire clearance your bike has, and you can experiment with different types of the tread to figure out what works best for your environment.
Are 700c Wheels Interchangeable?
Short answer: possibly.
Most 700c wheels can be interchangeable because the diameter of the wheel is the same. In other words, if a 700 fit on your bike in the past, it’s going to continue to fit on your bike in the future. The limiting factor is whether or not your bike can fit different tire widths. A lot of road bikes are set up with limited tire clearance, making it difficult to swap out for wider tires.
Let’s take a look at a specific example for more details:
Will 700x32c fit 700x35c?
Generally speaking, yes, a 700x32c can be used as a replacement for a 700x35c tire. The wheel diameter itself (700mm) isn’t changing, but the width of it will be. You can choose to increase or decrease the width of your tires depending on what kind of riding you want to do. Wider tires typically translate to more stability while more narrow tires can help with speed (plus they lighten the overall weight of the bike, albeit marginally).
In this case, we’re decreasing the width, which is usually doable. That said, you wouldn’t want to put super narrow wheels on a mountain bike, for example, because you’d lose a lot of stability and the bike may be too heavy for such small tires.
The biggest factor will be whether or not your bike has room for the tires. If you’re going for a slightly narrower tire (but maintaining the diameter), you should be fine. Putting wider tires on can be more difficult, though, so it really depends on the bike’s geometry.
Some bikes have very little clearance between the tire and the chainstay, making it impossible to add even a few millimeters. In other words, while your tire diameter (i.e. the “700”) needs to be exact, your tire width can vary depending on what your bike frame allows.
To make things more confusing, 700mm tires are roughly the equivalent of 29” tires.
However, the former is usually used for road bikes while the latter is for mountain bikes. You wouldn’t normally see a tire that uses a 700mm measurement that comes wide enough for a mountain bike.
What Does 700×35-43c Mean?
This is a common way for bike tube sizing to be listed. If you see a tube designation written this way, it means it can be used in any tires within 35mm-43mm wide. The 700 refers to the diameter of the wheel, so that number is firm depending on your rims.
In addition to knowing the correct tube size and width for your bike, you’ll want to make sure you choose the correct valve stem (the part that goes through the rim and allows you to fill your tires). Shrader valves are the most common type on the market.
These are often referred to as standard valves. The other two types of valve stems are Woods/Dunlop and Presta. Woods/Dunlop valve stems are incredibly rare and typically only found on bikes in the Netherlands or Asia. Presta valve stems are traditionally found on higher-end bikes due to their performance and are most often used by professional cyclists (Source).
What Is ISO in Tires ?
ISO is another way of measuring bike tires, but it lists the width first and then the diameter. Bike tires are measured nominally, which means the measurement is essentially a close estimate and not an exact number.
Using our 700x32c measurement as an example, the first number is for the outside diameter of the wheel, including tread. The second number is the width of the wheel. Both of these numbers can vary depending on manufacturing issues, tire pressure, and even the tread itself.
This is why some tire manufacturers have moved to include a second measurement system called ISO (International Standards Organization). You may also see it referred to as ETRTO for the European Tire and Rim Technical Organization (the group that originally came up with the method) (Source).
Instead of measuring the outer edge of the tire’s diameter, this method measures the tire’s bead, which is the surface that attaches to the rim. This helps to reduce confusion and limit ambiguity about whether or not a tire will fit a certain rim. Of course, it is still a nominal approximation and subject to varying tire pressures and rim widths (Source).
Tire Size Chart
Here’s an easy way to better understand different tire sizes and how it relates to the ISO. This is just an overview – there are many other sizes out there, but these are the most common.
| Tire Size | ISO | Use |
|---|---|---|
| 700c x 23mm-32mm | 622 | Road |
| 700c x 35mm-50mm | 622 | Gravel/Mixed Surface |
| 650b x 23mm-25mm | 584 | Small Road Bikes |
| 26” x 2.1”-2.3” | 559 | Cross Country Mountain Bike |
| 26” x 2.3”-2.5” | 559 | Trail Mountain Bike |
| 26” x 2.4”-2.6” | 559 | Enduro or Downhill Mountain Bike |
| 27.5” x 2.1”-2.3” | 584 | Cross Country Mountain Bike or Gravel Bike |
| 27.5” x 2.3”-2.5” | 584 | Trail Mountain Bike |
| 27.5” x 2.4”-2.6” | 584 | Enduro or Downhill Mountain Bike |
| 29” x 2.1”-2.3” | 622 | Cross Country Mountain Bike |
| 29” x 2.3”-2.5” | 622 | Trail Mountain Bike |
| 29” x 2.4”-2.6” | 622 | Enduro and Downhill Mountain Bike |
Final Thoughts
Hopefully you have a better grasp of where all these varying numbers come from. At the end of the day, all that matters is focusing on the tires that work for your bike. Have fun experimenting with different widths until you find a tire that suits your needs.
