Motorcycle Inch-to-Metric Converter
Find the metric size close to an old inch size. Use the calculator below. Results update as you type.
How the Motorcycle Inch-to-Metric Converter Works
The Motorcycle Inch to Metric Converter works by matching an inch-width motorcycle size to its approximate metric equivalent in a published correspondence table. Older bikes often list sizes such as 3.25-19.
- Enter the inch size, for example 3.25-19.
- Read the metric equivalent: 100/90-19.
- Read the alphanumeric code: MM90-19.
- Check fender and fork clearance before fitting.
The Formula
The Motorcycle Inch to Metric Converter formula is a table lookup, with Width (mm) ≈ Inch Width × 25.4 as a rough check.
Metric Size = Table[Inch Width] Width (mm) ≈ Inch Width × 25.4 Aspect ≈ 90 (most inch sizes)Worked example: 3.25 × 25.4 = 82.6 mm, but the published equivalent is 100/90. The table, not the arithmetic, gives the match. Inch widths describe an older measurement method that does not translate directly.
Conversion Table
The Motorcycle Inch to Metric Converter conversion table lists 8 inch widths with metric and alphanumeric equivalents. Pairs run from 2.50/2.75 (80/90, MH90) to 6.00/6.25 (150/80, MV85).
The note under the table cites the source and states that the sizes are approximate, not direct substitutes.
| Inch Width | Metric (90 series) | Width (mm) | Alpha Code |
|---|---|---|---|
| 2.50 / 2.75 | 80/90 | 80 | MH90 |
| 2.75 / 3.00 | 90/90 | 90 | MJ90 |
| 3.25 / 3.50 | 100/90 | 100 | MM90 |
| 3.75 / 4.00 | 110/90 | 110 | MN90 |
| 4.25 / 4.50 | 120/90 | 120 | MR90 |
| 5.00 / 5.10 | 130/90 | 130 | MT90 |
| 5.50 / 6.00 | 140/90 | 140 | MU90 |
| 6.00 / 6.25 | 150/80 | 150 | MV85 |
Approximate correspondence based on Continental's published motorcycle conversion chart; sizes are not direct substitutes.
What Is the Motorcycle Inch-to-Metric Converter?
The Motorcycle Inch to Metric Converter is a tool that translates legacy inch motorcycle sizes into modern metric sizes. Vintage and classic motorcycles often specify inch sizes that few makers still produce.
Metric equivalents are close, not identical. Check fender, fork brace and chain clearance before fitting a converted size.
Common Uses
The Motorcycle Inch to Metric Converter has 4 uses: vintage restorations, classic replacements, tube matching and catalog searches.
- Restore vintage bikes: Find a modern size for an old spec.
- Replace tires on classics: Find in-stock metric equivalents.
- Match tubes: Pick a tube for the converted size.
- Search catalogs: Search by metric size.