Motorcycle Tire Size Converter

Motorcycle tires use three different sizing systems — metric (120/70-17), imperial (3.25-19), and alphanumeric (MT90-16) — and the Motorcycle Tire Size Converter translates between all three so you can find a compatible replacement or cross-reference fitment. Select your input format, then enter your tire width, aspect ratio, and rim diameter (or pick your alphanumeric code for that format). You'll get the equivalent size in all three formats plus the overall tire diameter, sidewall height, and tire circumference.

mm

Width in millimeters for metric format

%

Sidewall height as percentage of width

inches
inches

For imperial format input

For alphanumeric format input

Results

Overall Tire Diameter

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Metric Format

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Imperial Format

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Alphanumeric Format

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Sidewall Height

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Tire Circumference

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Frequently Asked Questions

How do I read motorcycle tire sizes?

Motorcycle tire sizes follow different formats. Metric format (120/70-17) shows width in mm, aspect ratio as percentage, and rim diameter in inches. Imperial format (3.25-19) shows width and rim diameter in inches. Alphanumeric codes (MT90-16) use letters and numbers to represent dimensions.

What does the aspect ratio mean in tire sizing?

The aspect ratio is the sidewall height expressed as a percentage of the tire width. For example, in 120/70-17, the sidewall height is 70% of 120mm width, which equals 84mm sidewall height.

Can I use different tire size formats on the same motorcycle?

Yes, you can use equivalent sizes in different formats as long as the overall diameter remains close to the original. Use a converter to ensure compatibility and maintain proper speedometer accuracy and handling characteristics.

What's the difference between metric and imperial tire sizing?

Metric sizing uses millimeters for width and includes aspect ratio (120/70-17), while imperial sizing uses inches for both width and rim diameter (3.25-19). Imperial sizes don't specify aspect ratio, which is typically around 100%.

How do alphanumeric tire codes work?

Alphanumeric codes use letters to indicate tire width (M = medium range) followed by load rating and speed rating. For example, MT90 indicates a specific width range with a 90 load rating. These are commonly used on cruiser and touring motorcycles.

Why is overall tire diameter important?

Overall diameter affects speedometer accuracy, ground clearance, and handling characteristics. When changing tire sizes, try to keep the overall diameter within ±3% of the original to maintain proper motorcycle performance and safety.

What happens if I use the wrong tire size?

Using incorrect tire sizes can affect speedometer accuracy, handling, ground clearance, and safety. Larger diameter tires may rub against fenders or swing arms, while smaller ones can alter the motorcycle's geometry and performance characteristics.