Your bike tire size isn’t just a number on a spec sheet or the tire’s sidewall, it’s an important part of your bike setup. Your tire’s diameter and width play a big role in how your bike handles and feels, how fast it rolls, and how well it grips the road or trail underneath. It’s an important bit of info to know, especially when it comes time to replace your tires, or if you’re looking to test out different sizing.
Generally, the larger the tire and wheel is in diameter, the faster you’ll roll, and the easier it’ll be to roll over obstacles. But smaller wheels may be preferred by some for height or maneuverability reasons. Similarly, the narrower the tire, the faster it rolls—plus it’s lighter—while a wider tire will offer greater traction and stability. Below, we explain bike tire sizes, tire styles, rider height, and more.
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How do I know my bike tire size?
Bike tires come in all sorts of sizes, but it should be really, really easy to determine the size of yours. If you’re looking to purchase a replacement tire, simply look along the sidewall of your current tire (check both sides). You’ll see something printed like “700x25mm” or “29x2.30”—that’s your tire size.
You’ll also see the make and model of the tire, along with the recommended psi range for inflating your tire. Knowing how to measure your bike tire size is handy, but technically you shouldn’t need to measure anything in most circumstances because sizing is printed right on the tire.
What do bike tire size numbers mean?
Road, Gravel, and More
The first number refers to the diameter of your tire. The “700” that you will commonly see as the first number—especially on road bikes, gravel bikes, fixies, and more—denotes a 700-millimeter wide diameter tire. Another somewhat common size is 650mm, which is typically found on smaller adult bikes.
Accordingly, the second number refers to the metric width of the tire. Common widths for metric-based bike tires run anywhere from 23mm to as much as 48mm, or even more as gravel tires get increasingly wider.
Furthermore, you may see metric sizing listed as 700c or 650b. This is the older standard for sizing, where different letters represented different tire bead seat diameters. You will also see ISO sizing for tires, which is a more precise measurement for the tire bead seat diameter, though you usually won’t need to worry about it when picking out tires. For example, the ISO size of 622 corresponds with 700-size tires.
What’s a tire bead? Tire beads are the inner edges of the tire. They’re rounded and fit into the wheel rim to lock the tire into place once it’s inflated. A tire bead is said to be “seated” when it’s properly locked into place with the rim.
Mountain, Kid’s, and Fat Bikes
A significantly smaller first tire size number, like 29 or 26, means the tire diameter is sized in inches. This sizing is common for mountain bikes, kid’s bikes, fat bikes, and some hybrids. Modern mountain bike tires are now either 29 inches or 27.5 inches in diameter; 26 inches is the older standard, though many of those bikes are still in use. Fat bike tires are typically either 27.5 or 26 inches. Kid’s bike tires are usually anywhere from 12 to 26 inches.
The second number for tire width with this sizing is also listed in inches. Common mountain bike tire widths now range from 1.85 to 2.6 inches. Plus-size tires (sometimes called mid-fats) for mountain bikes are wider than typical mountain bike tires, but aren’t quite fat tires; they range from 2.8- to 3-inches wide. Actual fat bike tires require different (wider) rims. You’ll typically see fat bike tire widths range from 3 to 5.2 inches, and you may see their metric size listed as well.
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How to measure bike tire or wheel size
In the event that the size has worn off of the side of your tire (it likely won’t), you could use a caliper or tape measure to measure tire width and diameter. Or, if the bike has no tires to begin with, you can measure your wheel rim diameter—in the middle of the wheel from end to end—as a starting point. You could also look up or contact the bike or wheel manufacturer to see which tire(s) will be compatible.
How to measure bike tires or wheels for height
With adult bicycles, there are a few wheel size options, but it’s best to get a bike that’s sized to fit you well overall, as the frame size is more crucial to proper bike fit. Each bike company will have a size chart you can reference. Some bike companies do offer two wheel size options during purchasing, typically on smaller sized bikes, and that’s when you may need to decide between bike wheel sizes.
You may be able to put smaller wheels on a bike, depending on your frame and your brakes; rim brakes may not line up properly with a different size wheel. But you may also need to make other modifications (like crank length, for pedal clearance reasons). It’s often better, and easier, to have the right size bike from the start.
How to measure bike wheel size for kids
Kid’s bicycles, on the other hand, have a much wider range of tire sizes in order to accommodate a variety of heights. When you’re looking to purchase a new kid’s bike, the wheel size will correspond with the overall bike size, so it’s best to reference the bike manufacturer’s size chart. For example, the company Woom offers kid’s bikes in six different sizes and uses both height and inseam to help customers determine the right size bike and wheel combination.
Can I put wider tires on my bike?
You likely can, but there’s a limited range of tire-width compatibility for each bike. How wide you can go will depend on how much clearance you have with the tire installed between the fork arms, seatstays (or frame in general), and brakes (unless you have disc brakes). Beyond that, it’ll also depend on your wheel rims.
What type of bike tires do I need?
Here are the different styles you may encounter in your quest for new bike tires.
Clincher: This is the most common type of bike tire on the market now. Clincher tires use inner tubes to stay inflated and tire beads to attach to the rim. Inner tubes are not one-size-fits-all—you’ll need a tube that matches your tire diameter and width.
Tubeless: Tubeless tires are the newest style of bike tire. As its name suggests, tubeless tires don’t use inner tubes to stay inflated. Instead, they use tire sealant to create an airtight seal around the tire bead once inflated. If you’d like to convert to tubeless tires, you’ll need tubeless-compatible wheel rims.
Tubular: An older style of bike tire where the tire is glued to the rim. It’s less common now but is still utilized by some, including some pro road racers and cyclocross riders.
Beyond that, there are a variety of treads available for different sizes. Consider the kind of riding you usually do—do you ride pavement, gravel, both? A tire with more tread will offer better grip and is well suited for a variety of terrain, while a tire with little to no tread (like on many road bikes) will have less rolling resistance and will enable you to go faster.
And remember, when in doubt, your local bike shop is the best resource you have for figuring out all of your bike tire—and other bike—needs.
When she’s not out riding her mountain bike, Jessica is an editor for Popular Mechanics. She was previously an editor for Bicycling magazine.
