Motorcycle Tire Size Calculator
Diameter, Sidewall Height, Circumference & Revolutions per Mile for Metric, Alpha & Inch Tire Formats
REAL-WORLD EXAMPLE
A popular sportbike front tire 120/70ZR17 calculates to an overall diameter of about 23.6 inches with a sidewall height of roughly 3.31 inches. The matched rear 180/55ZR17 works out to about 24.8 inches in diameter. Because the front and rear diameters are different by design, checking each tire independently matters when swapping sizes — even a 3% change in the rear alone can noticeably shift the bike's geometry, ground clearance, and speedometer reading.
Motorcycle Tire Dimension Calculator
Enter your tire size in metric format — width in mm, aspect ratio as a percentage, rim diameter in inches. Add a second size to compare diameters.
Your Tire
50–360 mm
20–100 %
8–30 in
Comparison Tire (optional)
Fill all three fields to see diameter difference and speedometer impact.
Common Motorcycle Tire Dimensions
| Tire Size | Overall Dia. (in) | Sidewall (in) | Circumference (in) | Revs/Mile | Typical Use |
|---|---|---|---|---|---|
| 120/70ZR17 | 23.6 in | 3.31 in | 74.1 in | 856 | Sport Bike Front |
| 180/55ZR17 | 24.8 in | 3.90 in | 77.9 in | 815 | Sport Bike Rear |
| 130/90-16 | 25.5 in | 4.61 in | 80.1 in | 797 | Cruiser Rear |
| 100/90-19 | 26.1 in | 3.54 in | 82.0 in | 778 | Adventure / Dual-Sport Front |
| 150/70R17 | 24.9 in | 4.13 in | 78.2 in | 811 | Naked / Street Rear |
Values calculated from nominal P-metric geometry. Actual dimensions can vary by ±3–5 mm depending on brand, compound, and rim width. Always verify with the manufacturer's spec sheet for critical fitment decisions.
How to Use This Calculator
- Enter your motorcycle tire size in metric format (e.g. 120/70ZR17 or 180/55ZR17), alpha format (e.g. MH90-21), or inch format (e.g. 130/90-16 or 3.25H-19).
- Click 'Calculate Dimensions'.
- Review overall diameter, sidewall height, circumference, and revolutions per mile.
- Compare with another tire size using the second input to check diameter difference and speedometer impact before swapping.
Calculation Formulas & Sizing Format Guide
About Motorcycle Tire Dimensions
Why Accurate Dimensions Matter on a Motorcycle
On a car, a slightly mismatched tire mostly affects the speedometer and wear rate. On a motorcycle, small dimension changes also affect steering geometry, ground clearance, suspension behaviour, and the bike's ability to lean smoothly through corners. Front and rear motorcycle tires are typically different sizes by design, so you need to understand the dimensions of each separately when planning a size change.
Three Sizing Systems You Will Encounter
- Metric (e.g. 120/70ZR17): The most common format today, used on most sportbikes, nakeds, adventure bikes, and modern tourers. Width in mm, aspect ratio as a percentage, construction type (R = radial, B = bias-belted), and rim diameter in inches.
- Alpha (e.g. MH90-21): A letter code replaces the width number; used on some cruisers and touring bikes. Requires a conversion chart to match to a metric equivalent.
- Inch / Standard (e.g. 130/90-16 or 3.25H-19): Width expressed as a decimal inch, with or without an explicit aspect ratio. Common on older designs, many cruisers, and off-road bikes.
Key Measurements and What They Influence
- Overall Diameter: Affects speedometer accuracy, effective gearing, and ground clearance on both axles.
- Sidewall Height: Controls ride compliance, lean clearance angle, and how abruptly the tire transitions from upright to leaned.
- Circumference & Revs/Mile: Used when calibrating aftermarket speedometers, data loggers, or fuel injection / traction control systems after a tire swap.