(Last updated on March 6th, 2023)
Cycling is an amazing sport that offers fun and recreation to people all over the world. It is a great way to exercise, make new friends, and explore your local area. One amazing thing about cycling is that bikes come in all shapes and sizes.
This means they can be equipped with different parts and be made to make the experience better for you. An excellent upgrade you can make is changing your tire size. One thing that many cyclists find is that tire sizes can be difficult to understand.
In this article, we’ll tell you how to understand tire sizes properly and measure tires to ensure they fit your bike properly.
Image credit: Robbie Ferri
Why Is it Important to Have the Correct Tires?
Having the correct tires is vital when it comes to cycling. Here’s why you want to ensure you run tires that are compatible with your bike.
Safety
Tires that are too big for your bike can wear down the frame. Tires too small can risk damaging your wheels. Having the correct size tire ensures you don’t cause yourself any issues.
They Fit
If you buy the wrong tires, there’s a strong possibility that they won’t fit when you try to change them. The last thing you want is a set of useless tires sitting in the garage at home.
Performance
Bikes are designed to be used with certain tires. If you ride a gravel bike for long journeys and go for tires a little too small, you will not get the comfort or grip you originally had. If you put tires that are too big on them, it can cause a lot of lag. Certain factors contribute to the fastness of a bike tire.
Looks
If you don’t have the correct tires for your bike, it might make it look a little bit odd. Road tires on a mountain bike aren’t a good look. The same goes for mountain bike tires on a road bike.
Image credit: Robbie Ferri
How to Read a Tire Size
If you want to save yourself the trouble of measuring, you can just read the tire instead. Most tires come with special codes to tell you exactly what you are looking at. Typically they are written in two different ways, and we’ll speak about these next.
Standard Code
The first thing you want to look out for is the standard code. This will come in two different numbers.
The first will be the tire diameter.
Depending on if it’s a road or mountain bike, they can be a very similar size, according to industry standards. 700c on road bikes is 29” as far as mountain bikes go.
They are the same diameter, but because they are different disciplines called different names.
| 700c | Road bike standard similar to 29” in diameter | ||
| 650c | Road bike standard similar to a 27.5” in diameter | ||
| 650b | Gravel bike tire similar to 27.5” in diameter | ||
| 29” | Large mountain bike tire | ||
| 27.5” | Medium mountain bike tire | ||
| 26” | Small mountain bike tire |
Next, we have tire width, and this is where you have loads of different options to choose from. Again like the diameter, they are referred to under different standards.
| Road/Gravel | MTB/Fat |
| 23c | 23c |
| 25c | 2” |
| 2.2” | 2.1” |
| 30c | 2.2” |
| 32c | 2.3” |
| 35c | 2.4” |
| 38c | 2.6” |
| 40c | 3.0” |
| 45c | 4” |
| 50c | 5” |
Manufacturers Code
If you can’t find the standard code above, you will find the manufacturer’s code on the tire. Although it might look complicated, it is very easy to understand when you know what the numbers mean.
The code looks like this: 28-622.
Both numbers are very important and can tell you everything you need to know about the tire. What’s great about this number is that it works across all cycling disciplines.
The first number, 28, refers to the general width of the tire, which in this case would be 28mm.
| 28 | 28mm |
| 35 | 35mm |
| 40 | 40mm |
The second number is what we call the bead seat diameter. The bead seat diameter measures where the tire sits on the rim. In this case, it’s 622, equivalent to 700c road bike wheels and 29” mountain bike wheels.
| 622 | 29” / 700c |
| 584 | 27.5” / 650b |
| 559 | 26” |
| 507 | 24” |
| 406 | 20” |
These are only a few examples of the manufacturer’s code. The manufacturer’s code is the best way to understand a tire. It will tell you exactly what wheel the tire will fit on and the width the tire will be.
The manufacturer’s code is an excellent way to understand tires. It is especially useful when working on older bikes, as they come in awkward sizes.
Image credit: Robbie Ferri
What About Measuring Yourself?
Just say your tires have no markings or are so worn down that you can’t see them. What do you do then? Well, you’re going to have to measure the tires yourself. This is much easier than you might think when following our step-by-step guide.
Step One: Remove the Wheel
If you want to make this easy on yourself, start by removing the wheel and the tire together from the frame. You will now need to get a measuring tape and sit the wheel on the floor.
Image credit: Robbie Ferri
Step Two: Measure the Width
The first thing you need to do is measure the tire’s width. We recommend inflating the tire to ensure the measurement is fairly accurate. You must ensure it has a good shape if it’s off the wheel.
Measure from one side to the other. You will want to take the measurement in millimeters, which will be, for example, 23mm. This would equate to 23c standard code or 23 manufacturers code.
Image credit: Robbie Ferri
Step Three: Measure the Diameter
Measure from the center of the wheel’s edge to the outside in millimeters. Take this figure and double it; this will be our ISO diameter. For example, for us, this wheel comes out at 622.
This tire is a 23-622
Image credit: Robbie Ferri
Considerations to Make When Measuring Tires
When measuring tires, it’s important to take a few things into consideration that you might not have thought of.
Measuring off the Rim
When measuring off the rim, the tire doesn’t hold a very good shape, especially if it’s a performance tire. You want to ensure it’s in as natural shape as it would be on the rim and double-check to ensure you have it correct.
Classic Tires
Classic wheels and tires come in sizes such as 28”. This doesn’t mean they won’t fit a 700c wheel. This is because they are different sizes, they still share the same bead seat diameter. So many modern tires actually fit classic bikes.
Wide Rims
Wider rims make your tire stretch out further. For example, putting a road bike tire on a mountain bike wheel, will measure a few millimeters more in width.
Image credit: Robbie Ferri
Conclusion
When it comes to measuring tires, the best way to do it is by understanding the codes on the side. Typically every tire has one. If you can’t make it out, the good idea is to measure it on the rim, as we spoke about earlier.
When it comes to tires on your bike, it’s good to mix them up. There are so many options on the market to choose from that can give you extra speed or comfort.
You might want to consider tubeless tires. These are filled with sealant instead of an inner tube and can self-heal. They are more expensive, but they save you lots of money in inner tubes and trouble.
Frequently Asked Questions
You can either measure the tire itself, read the numbers on the side of the old tire, or check the bike specification.
No, 26” is much smaller than700c as far as tires go. 700c actually measures up to around 29”, so they are very different, and tires will not work with both.
Yes, you should be fine if the internal size of the tire is compatible with the inner rim width and bike.
The main difference is the wheel size. The 24” is smaller and more suited to children’s bikes and BMX.
700c in mm is 622mm hence the bead seat diameter on a 700c wheel is 622.
I’m Robbie Ferri, a writer from Norfolk in the UK. I love cycling, the gym, and have a huge passion for sharing my stories and knowledge to anyone with the time to read them. My main passion is cycling. I started eight years ago. In that time I have broken world records, cycled all over the world in Ultra Bikepacking races, and am lucky enough to have enjoyed some incredible times on two wheels with some incredible people. I have also worked in a bike shop and with some of the industries leading brands, not just promoting products but designing them too.
Under it all I am just someone very passionate about exploration and living a healthy lifestyle. Everything I do I put 100% into it and feel that life is for living. Never should you have a dull day.
