Why do motorcycle tire dimensions matter beyond basic fitment?

Overall diameter, circumference and revolutions per mile are calculated from the size marking. A change in overall diameter changes the speedometer reading in proportion (calculated). We have no official source for claims about handling, comfort or lean clearance from these dimensions, so we do not make them.

What are the three motorcycle tire sizing formats?

This calculator reads the metric format only: width in mm, aspect ratio and rim diameter in inches (for example 120/70ZR17). Alphanumeric and inch-format sizes (for example MH90-21 or 3.25-19) are marked differently; Michelin publishes size-marking and conversion tables on its motorcycle tire pages, and we do not convert them here.

How much can I change tire size safely on a motorcycle?

We have no official source for a safe size-change tolerance on motorcycles. The Continental 3% limit is car tire guidance and we have no motorcycle source, so treat any size change with care. Use the tire sizes approved in your motorcycle’s owner’s manual or by the motorcycle manufacturer.

Does a wider motorcycle tire always give more grip?

We have no official source comparing grip by tire width, so we make no claim. Use the tire sizes approved by your motorcycle manufacturer.

How do I use this calculator for alpha or inch-format tires?

Enter width in mm, aspect ratio and rim diameter. For an inch-format size such as 130/90-16 the first number is already the width and the second is the aspect ratio. We do not convert alphanumeric codes such as MH90; use the tire maker’s size table.

Can I use this calculator for scooter, dirt bike, or ATV tires?

The formula is the same for any tire marked width/aspect/rim, but real dimensions can differ from the formula. For example Dunlop publishes 27.95 inches for its MX34 80/100-21 where the formula gives 27.30. Confirm against the tire maker’s published dimensions.

Motorcycle Tire Size Calculator | Diameter, Sidewall & Revs (2026)

REAL-WORLD EXAMPLE

Example (calculated): 120/70ZR17 gives a sidewall height of 3.31 inches and an overall diameter of 23.61 inches; 180/55ZR17 gives 24.80 inches. These are formula results from the size marking. Real tires can differ: Dunlop publishes 27.95 inches for its MX34 80/100-21 where the formula gives 27.30, so check the tire maker's published dimensions.

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

Width (mm)

50–360 mm

Aspect Ratio (%)

20–100 %

Rim Diameter (in)

8–30 in

Comparison Tire (optional)

Fill all three fields to see diameter difference and speedometer impact.

Width (mm)

Aspect Ratio (%)

Rim Diameter (in)

Motorcycle Tire Dimensions (Calculated)

Tire Size	Overall Dia. (in)	Sidewall (in)	Circumference (in)	Revs/Mile
120/70ZR17	23.61 in	3.31 in	74.2 in	854
180/55ZR17	24.80 in	3.90 in	77.9 in	813
130/90-16	25.21 in	4.61 in	79.2 in	800
100/90-19	26.09 in	3.54 in	82.0 in	773
150/70R17	25.27 in	4.13 in	79.4 in	798

Values calculated from the size marking. Published dimensions for a specific tire can differ; verify with the tire maker.

How to Use This Calculator

Enter the tire width in mm, the aspect ratio and the rim diameter in inches, read from the size marking (for example 120/70ZR17 is 120, 70, 17).
Click 'Calculate Dimensions'.
Review overall diameter, sidewall height, circumference and revolutions per mile (all calculated).
Optionally enter a second size to compare diameters.

Calculation Formulas & Sizing Format Guide

Motorcycle Tire Dimension Formulas Input: • width_mm = tire section width in millimetres (first number in metric size) • aspect_% = aspect ratio as a percentage (second number; defaults to 100% for inch sizes) • rim_in = rim diameter in inches (last number) Step 1 — Sidewall Height: sidewall_mm = width_mm × (aspect_% ÷ 100) sidewall_in = sidewall_mm ÷ 25.4 Step 2 — Overall Diameter: overall_dia_in = rim_in + 2 × sidewall_in overall_dia_mm = overall_dia_in × 25.4 Step 3 — Circumference: circ_in = π × overall_dia_in Step 4 — Revolutions per Mile: revs_per_mile = 63,360 ÷ circ_in (63,360 = number of inches in a mile) Example: 120/70ZR17 sidewall_in = 120 × 0.70 ÷ 25.4 ≈ 3.31" overall_dia = 17 + 2 × 3.31 ≈ 23.61" circ = π × 23.61 ≈ 74.15" revs/mile ≈ 63,360 ÷ 74.15 ≈ 854 Note: these are nominal results from the size marking. Published dimensions for a specific tire can differ, so use the tire maker's figures where they exist. Use the tire sizes approved in your motorcycle's owner's manual.

About Motorcycle Tire Dimensions

Why Accurate Dimensions Matter on a Motorcycle

Overall diameter, circumference and revolutions per mile are calculated from the size marking. A change in overall diameter changes the speedometer reading in proportion. Use the tire sizes approved in your motorcycle’s owner’s manual. The speedometer correction for a new diameter and the revolutions per mile calculator work from the same numbers, and tire guides for each category are the cruiser, sport bike and dirt bike guides.

Size Format Used Here

The calculator reads width in mm, aspect ratio and rim diameter in inches. Alphanumeric and inch-format markings are not converted; Michelin publishes size-marking tables for those on its motorcycle tire pages.

Key Measurements

Overall Diameter: rim diameter + 2 × sidewall height (calculated).
Sidewall Height: width × aspect ratio ÷ 100 (calculated).
Circumference & Revs/Mile: π × diameter, and 63,360 ÷ circumference (calculated).

Frequently Asked Questions

Disclaimer

This calculator uses standard tire-geometry formulas and your inputs to compute theoretical dimensions. Actual tire dimensions can vary by several millimetres depending on the manufacturer, compound, rim width, and inflation pressure. Always verify fitment, clearance, and approved tire sizes against your motorcycle manufacturer's specification before fitting any non-OEM tire.

Motorcycle Tire Size Calculator