Motorcycle Tire Size Decoder
Decode metric motorcycle tire sizes, compare diameters side by side, and calculate speedometer error when fitting a different size.
Stock / Reference Tire (rear)
New / Alternate Tire (rear)
Size Comparison
Stock Tire
180/55R17
OD: 24.80" / 630 mm
Circumference: 77.9"
New Tire
190/55R17
OD: 25.23" / 641 mm
Circumference: 79.3"
Ride Height Change
+5.5 mm
Speedo Error
+1.7% (reads low)
How to Read a Metric Motorcycle Tire Size
180
Section width
Width of tire in millimetres at widest point
55
Aspect ratio
Sidewall height as % of section width (55 × 180mm = 99mm sidewall)
R
Construction
R = Radial · B = Bias belted · (blank) = Bias
17
Rim diameter
Rim size in inches
Common Front Tire Sizes
| Size | OD (inches) | Sidewall (mm) |
|---|---|---|
| 120/70R17 | 23.61" | 84 mm |
| 110/80R19 | 25.93" | 88 mm |
| 90/90-21 | 27.38" | 81 mm |
| 100/90-19 | 26.09" | 90 mm |
| 130/70R17 | 24.17" | 91 mm |
| 80/100-21 | 27.30" | 80 mm |
| 100/100-18 | 25.87" | 100 mm |
Fitment Notes
• Always verify the rim width range listed on the tire sidewall before fitting.
• A wider tire raises ride height and affects handling (more trail, heavier steering).
• Check chain / swingarm clearance before fitting an oversized rear tire.
• Speedometer reads low when a taller tire is fitted (more distance per revolution than the ECU/speedo expects).