Road Bike Tire Sizes | An In-Depth Guide

Bike tires are probably the most important components of any road bike under $2000. While your bike traditionally comes with manufacturer-provided tires, at some point you will need to replace them. On face value, the idea of buying bike tires may seem like a pretty easy and straightforward thing. But more often than not, many bike owners tend to get it wrong, especially when it comes to road bike tire sizes.

Each bike has a specified wheel size. In essence, you are expected to buy tires that fit perfectly to the rim just as you would buy road bike saddles that fit you. The great news is that bike sizes are standardized so you don’t need to do difficult calculations to figure out the ideal size for your bike.

Whether you’re looking for a normal size bike tire, an ISO size, a 27” tire, Euro Size, or even 700C, we are going to give you the information in this post that will help you find exactly what you need.

Traditional Road Bike Tire Sizes

Sizing systems for road bike tires are totally based on the tire’s outer diameter. However, it’s still important to consider the rim size when deciding on the most appropriate tire size. Different tire manufacturers have put in place various standardized tire measurements to help you decide what works best for your bike.

We are going to take a look at these standardized measures and what they mean.

ISO or International Organization for Standardization

As you can probably guess, ISO stands for the International Organization for Standardization. The ISO tire size standards are probably the most globally acceptable and they are based on a very simple premise. ISO tire measurements are based on the width and the diameter of the tires.

Tire Width

The tire width is also very important in determining actual road bike tire sizes. You will notice that on the sidewall of your tires, there are two measurements separated by x. The first measurement is often the diameter, which is relatively larger and the second one is always the width.

Let’s say, for example, a tire with a specified size of 700 x 23. This means that it has a diameter of 700mm and a width of 23mm. The width determines the contact surface between the tire and the road. In essence, tires with a relatively higher width specification tend to be more stable and would offer better tread compared to those that have a smaller width specification.

Traditionally, women’s road bikes have three main width specifications. They include 23c, 25c, and 28c. Please note that the “c” in the width doesn’t stand for centimeters. The measurements are still in millimeters. The “c” is basically included as part of old French-based classification systems but has got nothing to do with the actual width measurements of the tire.

So, how do you figure out the ideal tire width? Well, it depends on your riding needs. For those of you who will be riding on tougher terrain, go for 28mm. 

Racers who prefer speed over anything else, a lower width of 23mm is highly recommended. But for the perfect balance between comfort and performance, 25mm should do.

Tire Diameter

The diameter of the tire is a key factor in determining size classification. In most cases, the actual outer diameter of the tire will vary from one tire to the next based on many factors such as the tread pattern. But there’s a remedy for that.

Instead of using the outer diameter as a standard measure, manufactures may decide to use the inner diameter in order to offer users more standardized road bike tire sizes for which you can use a bike tire pressure gauge correctly. You can find diameter measurements on the sidewall of your tire. 

The width of the tire will also be included with the diameter as well just to give you a clear picture of how big or small the tire is.

28 vs. 29-Inch Road Bike Tire Sizes

It’s common to find tire sizes specified in inches. The most commonly used options are the 28 and the 29 inches. 

But what’s the difference between the two? Well, in most European countries, the 28-inch tire is seen as the traditional option for racing and touring. It’s also the most frequently used tire size in most European countries.

29-inch road bike tire sizes, on the other hand, are fairly recent and are more often found in American mountain bikes. The difference in specifications may not be felt if you are riding on flat surfaces. But on harder terrains, you’re more likely to have an easier time with a 29-inch tire than a 28 inch one.


Buying a quality tire for your bike for bad knees isn’t always an easy thing but you just need to know what the specs mean.

A good rule would be to look at the specs on your previous tires and buy exactly the same thing. But you can use the guide above to give yourself a new riding experience with new tires.

Shailen Vandeyar

A proud Indian origin Kiwi who loves to plant trees and play with my pet bunny when not out doing about every kind of biking and experiencing the occasional tumble. Ready to share the ride with you.

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