A motorcycle tire size chart gives you a fast way to decode the numbers and letters molded into a tire’s sidewall, but it is only the start of a fitment decision. The replacement must match the motorcycle’s approved rim diameter and should meet or exceed its required load and speed capability. Width, overall diameter, construction, tread profile, front or rear designation, and the tire maker’s fitment guidance also matter. Use the chart below to translate the marking, then compare the proposed tire with your owner’s manual, the tire information label if fitted, and the motorcycle and tire manufacturers’ recommendations before ordering.
Most current street motorcycles use a metric tire marking such as 180/55 ZR17 M/C (73W). Dirt bikes, cruisers, older motorcycles, and some scooters may use inch-based or alphanumeric markings instead. A motorcycle tire size chart translates each segment, but it cannot tell you by itself whether a particular tire model is approved for your motorcycle.
| Sidewall marking | What it identifies | Example | What to check |
|---|---|---|---|
| 180 | Nominal section width in millimeters | 180 mm | Chain, swingarm, fender, and adjacent-component clearance |
| 55 | Aspect ratio: sidewall height as a percentage of width | 55% of 180 mm | Overall diameter and handling changes |
| R, B, or “-” | Construction type | R = radial; B = belted bias; - = bias-ply | Motorcycle and tire manufacturer compatibility guidance |
| 17 | Rim diameter in inches | 17-inch rim | Must match the wheel exactly |
| M/C | Motorcycle-specific designation | M/C | Do not treat it as a sizing measurement |
| 73 | Load index code | 73 | Required load capacity for the axle and intended use |
| W or (W) | Speed symbol | W or (W) | Required speed category and any manufacturer restrictions |
For the example above, 180 is the nominal tire width. The 55 aspect ratio means the sidewall height is nominally 55 percent of 180 mm, or about 99 mm. That calculation helps compare sizes, but it is not a promise of exact mounted dimensions. Rim width, tire construction, inflation pressure, and the tire maker’s design can all affect the tire’s measured shape.
| Tire size | Nominal width | Nominal sidewall height | Rim diameter | Typical fitment question |
|---|---|---|---|---|
| 110/70 R17 | 110 mm | 77 mm | 17 inches | Is the front rim width within the tire maker’s approved range? |
| 120/70 ZR17 | 120 mm | 84 mm | 17 inches | Does the replacement retain the required front load and speed rating? |
| 150/70 R17 | 150 mm | 105 mm | 17 inches | Is it approved for the bike’s rear wheel and intended luggage or passenger load? |
| 180/55 ZR17 | 180 mm | 99 mm | 17 inches | Will the selected model clear the chain and swingarm on the specified rim? |
| 200/50 ZR17 | 200 mm | 100 mm | 17 inches | Is this an approved alternative rather than simply a wider tire? |
The chart is most useful for identifying meaningful differences. For example, a 180/55 tire and a 180/60 tire share nominal width and rim diameter, but the 60-series tire has a taller nominal sidewall. That can change overall diameter, lean behavior, ride height, speedometer accuracy on motorcycles that read wheel speed at that axle, and clearance under the fender or near the swingarm.
The letters are easy to overlook because riders often focus on the three main numbers. They can be just as important as the dimensions.
Do not assume that radial and bias tires are interchangeable solely because they share a size. Some motorcycles specify a particular construction for one or both axles. Mixing construction types can also be subject to motorcycle or tire manufacturer restrictions. Check the approved replacement guidance for your model before changing from the original construction.
A motorcycle tire size chart should also cover older and cruiser-style formats. One common inch-based marking is 4.00-18. In that style, 4.00 is a nominal width in inches and 18 is the rim diameter in inches. The dash commonly indicates bias-ply construction. Unlike a metric size, the aspect ratio is not explicitly stated.
Alphanumeric sizes, such as MT90B16, combine a lettered width or profile category with construction and rim diameter. The exact meaning and metric equivalent can vary by the tire maker’s conversion guide, so do not use a generic conversion table as final fitment approval. A tire listed as an apparent equivalent may have a different profile, load capability, or approved rim-width range.
| Marking style | Example | What the reader can identify | Important limitation |
|---|---|---|---|
| Metric | 120/70 R17 | Width, aspect ratio, construction, and rim diameter | Actual mounted dimensions can differ by tire model and rim width |
| Inch-based | 4.00-18 | Nominal width and rim diameter | Aspect ratio is not directly printed |
| Alphanumeric | MT90B16 | Size class, construction, and rim diameter | Use manufacturer-specific equivalency information |
| Flotation-style | 25x8-12 | Overall diameter, width, and rim diameter | More common on certain off-road machines and not directly comparable to metric road tires |
Buying the same size printed on the old tire is often a sensible starting point, but the old tire may not be the original approved size. A previous owner may have installed a nonstandard tire, selected a tire outside its suitable rim-width range, or changed wheel sizes. Confirm the motorcycle’s specified front and rear tire sizes before treating the tire currently fitted as the reference.
Even an exact-size replacement can differ in its real-world dimensions. Tire manufacturers publish specification data for many tire models, including approved rim widths, measured rim width, section width, and overall diameter. Those figures are more useful than the sidewall code when clearance is tight or when changing brands.
Load index is a coded value, not a weight printed in pounds. A tire manufacturer’s load-and-inflation information converts that code into a maximum load at specified conditions. Because motorcycles place different loads on front and rear tires, use the axle-specific requirements in the owner’s manual or manufacturer fitment information rather than assuming two equal-looking tires need the same rating.
The speed symbol indicates the tire’s speed category under standardized test conditions. Parentheses can matter: a marking such as (W) is distinct from W. The tire’s technical documentation provides the proper interpretation and operating conditions. Never reduce the speed category below the motorcycle manufacturer’s specification simply because your normal riding speeds are lower.
Load and speed ratings do not override the motorcycle’s own limits. They also depend on correct inflation pressure, proper installation, sound wheel condition, and staying within the motorcycle’s stated weight limits. An overloaded bike or underinflated tire can overheat and perform poorly even if the sidewall’s load index initially appears adequate.
The most expensive errors usually happen before installation. Avoid making a purchase based on one number, a broad online fitment filter, or an assumed conversion between old and new tire formats.
An alternate size can be appropriate when the motorcycle manufacturer lists it as an approved option, when an accessory wheel package has documented fitment guidance, or when a tire manufacturer provides a model-specific recommendation. It may also be considered for a dedicated use case, such as certain off-road setups, but only after confirming all affected specifications.
Choose an alternate size only if it has a clear reason and verified compatibility. Its advantage may be availability or a tire model better suited to your riding conditions. Its limitation is that a small change in section height or profile can have consequences that are not visible in a simple motorcycle tire size chart. If no authoritative guidance supports the change, stay with the specified size.
They fit the same nominal 17-inch rim diameter and share the same nominal width, but the 60-series tire has a taller sidewall than the 55-series tire. That can change overall diameter, handling, gearing feel, and clearance. Use the 180/60 only if your motorcycle, wheel, and selected tire model support it.
Only if the tire manufacturer approves that tire size for your actual rim width and there is adequate motorcycle clearance. A wider tire on the same rim may not create the intended contact patch and can change steering response. Check the motorcycle manufacturer’s approved sizes as well as the tire maker’s rim-width range.
Yes. A different aspect ratio changes the tire’s nominal sidewall height and can alter overall diameter and profile. On a motorcycle, those changes may affect ride height, turn-in behavior, lean characteristics, and clearances, so it should not be treated as a cosmetic difference.
M/C identifies the tire as a motorcycle tire. It does not tell you the rim width range, load capacity, speed capability, or whether the tire is approved for your motorcycle. Read the remaining sidewall code and product documentation as well.
Not necessarily. The required specifications can differ by axle and motorcycle model. Each replacement tire should meet or exceed the applicable original requirement and be appropriate for its designated front or rear position.
The sidewall pressure is generally associated with the tire’s maximum load conditions, not a universal everyday setting for your motorcycle. Start with the cold inflation pressure specified by the motorcycle manufacturer, then follow any approved adjustments for load or riding conditions. Do not exceed the tire or wheel limits.
A motorcycle tire size chart helps you decode the essential information: nominal width, aspect ratio, construction, rim diameter, load index, and speed symbol. Use it to narrow the choices, not to make the final call from sidewall numbers alone. The safest purchase is a tire in the motorcycle’s approved size that matches the correct axle position, wheel type, load and speed requirements, and intended riding use, with the exact tire model checked against manufacturer fitment data before installation.