Find the size printed on the tire sidewall

The fastest way to check your bicycle tire size is to look at the sidewall of the tire itself. Manufacturers print the tire dimensions on the rubber, usually near the bead (the edge that sits on the rim). You do not need any tools — just spin the wheel so you can see the side of the tire clearly, and read the numbers stamped or molded into the rubber.

The size appears as a series of numbers and letters. On most modern bicycles, you will see a format like 700x28c or 26x2.0. The first number is the wheel diameter in millimeters (or inches on older bikes), and the second is the tire width. The letter at the end, if present, indicates the tire profile or bead seat diameter and is less important for basic sizing.

If the tire is worn smooth or the printing has faded, you may need to look at the rim or check your bike's original documentation. Many tire sidewalls also list the tire pressure range (measured in PSI or bar), which is useful information to keep nearby.

Key Takeaways

  • Tire size is printed on the sidewall of the tire in a format like 700x28c or 26x2.0, where the first number is wheel diameter and the second is width.
  • You can read the size without removing the wheel — straightforward rotate it to see the sidewall clearly and look for the stamped or molded numbers.
  • If the sidewall printing is illegible, check the rim itself or your bike's original paperwork, which often lists the original tire size.
  • The tire pressure range is also printed on the sidewall and tells you the safe PSI or bar range for that specific tire.
  • Knowing your exact tire size is necessary when buying replacement tires, tubes, or checking compatibility with your bike's frame and brakes.

Check the rim if the tire sidewall is worn

If the tire is too worn to read clearly, the rim itself often has size information molded or stamped into it. Spin the wheel and look at the inner edge of the rim where it meets the tire. The size may be less prominent than on the tire, but it is usually there.

Rims are marked with the bead seat diameter (BSD) and sometimes the internal width. This information is slightly different from tire width, but it will point you toward the correct tire size. If you find a rim marking like 622 or 559, these are the bead seat diameters in millimeters — you can use these numbers to cross-reference the tire size you need.

Understand the two common tire sizing systems

ISO (metric) sizing is the modern standard and appears as two numbers separated by a dash or "x" — for example, 700x28c or 622x28. The first number is the bead seat diameter in millimeters, and the second is the tire width in millimeters. This system is used on road bikes, gravel bikes, and most modern mountain bikes.

Inch sizing is older and still found on many mountain bikes and children's bikes. It looks like 26x2.0 or 20x1.75, where the first number is the wheel diameter in inches and the second is the tire width. If your bike uses inch sizing, the numbers will be smaller and less precise than metric sizes.

A single wheel diameter can fit multiple tire widths. A 700c wheel, for instance, can accept tires ranging from about 23mm to 50mm wide, depending on your frame clearance and brake type. Always check both numbers when ordering a replacement tire to may support it fits your bike.

Measure the tire width if you need exact dimensions

If you are replacing a tire and want to confirm the width beyond what the sidewall says, you can measure it yourself with a ruler or calipers. Deflate the tire slightly so it sits naturally on the rim, then measure straight across the widest part of the tire. This measurement should match the width number on the sidewall.

Measuring is most useful when you are comparing an old tire to a new one, or when the sidewall printing is partially illegible. Keep in mind that tire width can vary slightly depending on the rim width and air pressure, so a measurement is a check, not a replacement for reading the sidewall.

Look up your bike's original tire size in the manual or receipt

If you cannot read the tire or rim clearly, your bike's original documentation often lists the tire size. Check any paperwork that came with the bike — the owner's manual, the original receipt, or a sticker on the frame. Many manufacturers also print tire size on a sticker under the seat tube or on the head tube.

If you bought the bike used and have no paperwork, you can contact the manufacturer with your bike's model and year, and they can tell you the original tire size. This is especially helpful if you are unsure whether the current tires are original or have been replaced.

Know why tire size matters for replacement and safety

Checking your tire size before buying a replacement is critical because installing the wrong size can damage your rim, cause the tire to slip, or create unsafe handling. A tire that is too narrow may not seat properly on the rim. A tire that is too wide may rub against your frame or brakes and could cause a crash.

Tire size also affects how your bike rides. A wider tire at lower pressure absorbs bumps better and offers more grip, while a narrower tire rolls faster on smooth pavement. When you replace a tire, matching the original size keeps your bike's handling and performance consistent unless you have a specific reason to change.

Frequently Asked Questions

What do the letters at the end of a tire size mean?

The letter indicates the bead seat diameter standard. Common letters are "c" (622mm), "b" (635mm), and "a" (630mm). For most modern bikes, you only need to match the number part of the size — the letter will be the same on any replacement tire that fits your rim.

Can I use a different tire width on the same wheel?

Yes, within limits. A 700c wheel can accept different widths, but your frame and brakes must have clearance. Check your bike's manual or measure the space between the tire and frame when the wheel is centered. Going wider than the frame allows can cause rubbing and is unsafe.

What is the difference between tire size and tube size?

Tubes are sized by wheel diameter and width range, like 700x25-32c. The range means the tube fits tires between 25mm and 32mm wide on a 700c wheel. Always match the wheel diameter exactly, but the width range gives you some flexibility as long as your tire falls within it.

Do I need to check tire size if I am just replacing the tube?

Yes. Tubes are sized by wheel diameter and width range. Using a tube that is too small or too large for your tire can cause pinch flats or valve stem damage. Always check both your wheel diameter and tire width before buying a replacement tube.

Where is tire size listed if my bike is very old?

Older bikes often use inch sizing (like 26x1.75) printed on the sidewall. If the printing is gone, check the rim or contact the bike manufacturer if you know the brand and model. Vintage bike forums can also help identify the size based on photos of your bike.