| Label on the tire | Bead seat | Usually on |
|---|---|---|
| 26 x 1.5 to 26 x 2.6 (decimal width) | 559 mm | Mountain bikes, cruisers, many touring bikes |
| 26 x 1 3/4, 650C | 571 mm | Small triathlon/road bikes, some old cruisers |
| 26 x 1 3/8 (English), 650A | 590 mm | Raleigh-style three-speeds and roadsters |
| 26 x 1 1/4, Schwinn 26 x 1 3/8 | 597 mm | Old club bikes, Schwinn lightweights |
The quick test
- Decimal width (26 x 1.95, 26 x 2.1): it’s 559. Almost all modern 26-inch tires are this.
- Fraction width (26 x 1 3/8): it’s one of the older sizes. Look for the ETRTO number on the sidewall – 37-590 or 32-597 – before buying.
- Old Schwinn? Schwinn used its own 26 x 1 3/8 (S-6, 597 mm) that does not fit English 26 x 1 3/8 rims (590 mm), even though the label is identical.
Why it happens
Inch sizes once described the tire’s outside diameter. A fat tire on a small rim and a thin tire on a larger rim both came out around 26 inches, so both were called 26-inch. Rims changed, the names stayed. The ISO 5775 system (the ETRTO numbers) names the rim in millimetres to end the confusion.
Type your exact label into the size decoder to see which one you have.