Motorcycle Alphanumeric Size Converter
Read old codes such as MT90-16. Use the calculator below. Results update as you type.
How the Motorcycle Alphanumeric Size Converter Works
This converter works by reading the width letter in a code such as MT90-16 and matching it to a metric width. The M marks motorcycle use, the second letter marks width and the number marks aspect ratio.
- Enter the code, for example MT90-16.
- Read the width letter: T.
- Read the metric equivalent: 130/90-16.
- Read the width: 5.12 in and the sidewall: 117 mm.
The Formula
The formula is a table lookup: Metric Width = Letter_Table[Second Letter], and Sidewall = Width × Aspect ÷ 100.
Metric Width = Table[Letter] Sidewall (mm) = Width × Aspect ÷ 100Worked example: MU90 maps to 140/90, so the sidewall is 140 × 0.90 = 126 mm (4.96 in).
Conversion Table
The conversion table lists 10 alphanumeric codes from MH90 to MV85 with metric equivalents, width and sidewall. Width letters run H, J, M, N, P, R, T, U, V.
MP85 maps to a 110/90 rear in the source table. Alphanumeric codes are mostly found on American V-twin cruisers.
| Code | Width Letter | Metric Equivalent | Width (in) | Sidewall (mm) |
|---|---|---|---|---|
| MH90 | H | 80/90 | 3.15 | 72 |
| MJ90 | J | 90/90 | 3.54 | 81 |
| MM90 | M | 100/90 | 3.94 | 90 |
| MN90 | N | 110/90 | 4.33 | 99 |
| MP85 | P | 110/90 (rear) | 4.33 | 99 |
| MR90 | R | 120/90 | 4.72 | 108 |
| MT90 | T | 130/90 | 5.12 | 117 |
| MU85 | U | 140/85 | 5.51 | 119 |
| MU90 | U | 140/90 | 5.51 | 126 |
| MV85 | V | 150/80 | 5.91 | 120 |
What Is the Motorcycle Alphanumeric Size Converter?
The Motorcycle Alphanumeric Size Converter is a tool that interprets legacy alphanumeric motorcycle tire codes. The alphanumeric system was common on US motorcycles in the 1970s and 1980s.
Each code combined a width letter and an aspect ratio. Modern tires for these bikes are sold in either the alphanumeric code or the metric equivalent.
Common Uses
This converter has 4 uses: cruiser replacements, catalog cross-reference, manual decoding and tube selection.
- Replace cruiser tires: Find metric equivalents for V-twins.
- Cross-reference catalogs: Search both size systems.
- Decode manuals: Read sizes in old service manuals.
- Select tubes: Match tube size to the code.