For something as simple as the diameter and the width of a round and hollow piece of rubber that’s mounted on a rim, bike tire sizes can be surprisingly confusing.
Nowhere is this more true than in road bike tires, where—largely thanks to the remnants of a French tire sizing system that’s no longer in use—what’s written on the sidewall isn’t necessarily what the tire or the rim measure in diameter.
The standard size for a road bike tire is 700c x 23mm. The “700c” is a reference number and a relic from an old French tire sizing system that refers to the outer diameter of the tire. A 700c tire fits on a wheel with a bead seat diameter of 622mm.
These days, bicycle tire manufacturers continue to use this reference code, followed by the lowercase letter “c,” to indicate that a tire has a bead diameter of 622mm.
A 700c x 23mm tire, often written as 700x23c, is the same size as a 622mm x 32mm tire. These tires are also known as “ISO 622” tires after the international labeling standard that they follow.
Road Bike vs. Mountain Bike Tires
700c tires, or “700’s” are standard sized tires that fit most road bikes, hybrid/commuter bikes, and gravel bikes. If you see a bike with narrow tires, there’s a high chance they are 700c tires.
Matters are complicated further by the fact that the size of mountain bikes tires is given in inches instead of millimeters. Common sizes for mountain bike tires are 26, 27.5, and 29 inches in diameter. (With smaller tire sizes also available for children’s bikes.)
Although tire sizing systems and tire sizes may seem like a mystery at first glance, the good news is that once you become familiar with them, you can’t make a mistake and buy the wrong tire size.
Related: Are Bike Tires and Inner Tubes the Same Size?
Bike Tire Sizes, Explained
The size of your tires can be found on their sidewalls.
Tire size is typically listed as Diameter x Width (although you may occasionally find Width x Diameter). The diameter on tires is the diameter of the bead; following this logic, the diameter on rims is the diameter of the bead seat.
Your bike tire’s diameter has to exactly match the diameter of your rim.
Bike wheel size is standard. A good rule of thumb is that standard wheel sizes are 622mm for 700c or 29-inch bikes, 584mm for 27.5-inch bikes, and 559 cm for 26-inch bikes. The inner diameter of your bike’s bead should match the rim’s bead seat.
The width of your bike tires can vary slightly, which means you do have leeway in the width of tires you choose for your bike.
For many road bikes and hybrid bike tires, you will see something like 700 x 28c. The first number is the three-digit reference code for the diameter; the second is the width measured in millimeters. (Not centimeters–don’t let the “c” confuse you.)
In some cases, the wheel size might be listed along with the with. For example, 622mm x 23mm.
Mountain bike tires, on the other hand, will say something like 26 x 2.40. This means diameter of 26 inches by 2.40 inches width.
What Does 700c Stand For?
In the old French tire sizing system, 700a, 700b, 700c, and 700d were different types of tires that fit different types of rims, none of which were interchangeable.
As the late Sheldon Brown of Harris Cyclery explained, 700 is an approximation of the intended outer diameter of the tire. Go to a bike shop and look at the hybrid bikes’ tires, and you will notice many of them are fitted with 650c tires.
As time went on, manufacturers settled on the size 700c x 23mm as the most common tires for road racers and tourers. This size fits a bead seat diameter of 622mm, which has remained constant, and has a width of 23 millimeters.
All the other 700 sizes—700a, 700b, and 700d—fell into disuse and are no longer made today. (Though there are those who restore them.)
What is the Difference Between 26-Inch and 700c Tires?
If you have gone out to check the tire size on your mountain bike since you started reading this, you might notice that your tires indicate a diameter of 26.
Early mountain bikes generally had standard 26-inch tires, so this became an alternative to the 700c. Nowadays mountain bike tires come in larger sizes as well, generally 27.5 inches or 29 inches.
A 26 inch tire fits a wheel with a diameter of 559 mm, so it is a little smaller in diameter than the 700c. The 26-inch tire may also be wider than the 700c tire, so don’t forget to check the tire width.
Are 700c Tires the Same as 29-Inch Tires?
Both 700c tires and 29-inch tires will fit a rim that has a diameter of 622mm. If you are looking at diameter only, the tires should be interchangeable.
Keep in mind, however, that the width of the tire and the width of the bead seat rim varies.
Road bike rims generally have narrower bead seats (where the tire sits against the wheel) than mountain bike tire. Likewise, mountain bike rims have wider bead seats to accommodate the wider tires.
While 29-inch tires are the same as 700c tires in terms of diameter, the two may not be interchangeable due to the width of the tire. If you are thinking of switching between the two types of tire, it might be a good idea to check out the tires at a bike shop.
What Are 650b Tires?
You may have noticed that 700c are not the only tires that stick to the old system.
Some mountain bikes and gravel bikes these days will have 650b tires, which fit the same wheel diameter as a 27.5 inch tire (584mm).
Some riders might prefer these wheels to the larger 700c wheels, without going all the way down to a 26 inch tire. Smaller wheels can mean a larger volume tire fits on the same frame, which might improve traction and handling.
They may be lighter than the 700c rims, though the weight difference may be offset by the larger width of the 27.5 inch tires.
Generally it is a matter of personal preference. You can read more about 650b tires at BikeRadar.
In Conclusion
Getting your head around the sizes of bike tires takes a little getting used to, but once you start comparing tires it will begin to make sense.
You can change out the size of your tires for new tires if your frame allows. You may be ready to try a slightly wider tire if your rims allow. Often the size and width of tire is personal preference, so you might want to try out a few options.
If you have questions, visit your local bike shop and have them show you the different types of tires that will fit your bike. Tire size is not the only consideration, of course. You will also need to determine what width or tread you prefer and what is best for the type of bicycling you intend to do.
