How road tire sizes are written
Road tires are usually labeled with more than one sizing system, and that is the main source of confusion. You may see three styles:
- ISO / ETRTO (for example, 28-622): the first number is the tire width in millimeters, and the second is the bead seat diameter, which is the diameter of the rim where the tire sits. This is the most precise system.
- French metric (for example, 700x28C): 700 is a rough outer diameter and 28 is the width in millimeters. The “C” is a leftover from older width codes.
- Imperial / inch (for example, 27 x 1-1/4 or 28 x 1.5): common on older bikes and some city bikes. These labels are less reliable, so match them to the ISO number where you can.
Reading the sidewall
Look on the side of your current tire for a stamped label. A modern road tire often shows something like “28-622” or “700x28C”, sometimes both. Also look for a maximum pressure rating and any note about tubeless or tube-type use. If the tire is worn or the print is faded, check the rim or the bike’s original specifications instead.
The bead seat diameter is the number that must match your rim. The width is where you have some choice.
700c, 28 inch and 622: the same thing?
For road bikes, 700c wheels have a 622 mm bead seat diameter. The same 622 mm diameter is also called “28 inch” on many European and city bikes, and 29-inch mountain bike wheels share it as well. That means the tire diameter can be compatible across those labels, but you still need to check width, rim fit and frame clearance. A 29 x 2.4 mountain tire, for example, has the same bead diameter as a road tire but is far wider than most road frames allow. The sibling guides on gravel tire width and mountain bike tire dimensions cover that overlap.
Choosing a width
Many current road bikes are sold with tires somewhere in the mid-20s to around 30 mm, and wider tires are increasingly common. A wider tire generally runs at lower pressure and can feel more comfortable, while a narrower one is lighter. There is no single right answer, and it depends on your roads, rim, and frame. See 25mm vs 28mm for road bikes for a closer comparison.
Checking frame and brake clearance
Before going wider than what you have now, check:
- the space at the fork crown, seat stays, chainstays and brake calipers
- that there is a few millimeters of gap on each side once the tire is inflated, because tires can measure differently from their label
- the maximum tire width listed by the frame or fork maker, if available
Manufacturers such as Schwalbe note that real tire width can differ from the label, which is a reason to measure rather than trust the number alone.
Checking rim compatibility
Each tire width works with a range of internal rim widths. Check the tire and rim makers’ charts, and if their limits differ, follow the more restrictive one. Hookless rims have extra requirements, including tire compatibility and pressure limits. Our guide on matching tire width to rim width walks through this.
Step-by-step: find the right size
- Read the size stamped on your current tire (or find and measure your tire size if it is unreadable).
- Note the bead seat diameter (such as 622) and the width.
- Check your rim’s internal width and any manufacturer limits.
- Measure clearance in the frame, fork and brakes.
- Choose a width within the range that all of these allow.
- Confirm the tube size or tubeless setup matches the new tire.
Common mistakes
- Matching only the “700c” label and ignoring width.
- Assuming a tire will measure exactly its label width.
- Ignoring rim limits, particularly on hookless rims.
- Forgetting that the inner tube must match the tire size range.