Bicycle Bead-Seat Diameter Checker
Check that the tire and rim are the same size. Use the calculator below. Results update as you type.
Overall Diameter = (Rim Diameter × 25.4) + 2 × (Width × Aspect Ratio / 100)How the Bicycle Bead-Seat Diameter Checker Works
The Bicycle Bead Seat Diameter Checker works by comparing the tire's ISO bead seat diameter with the rim's bead seat diameter. The 2 numbers must be equal.
- Read the tire's ISO size, for example 57-584.
- Read the rim's ISO size, for example 584x25.
- Compare the BSD numbers: 584 and 584.
- Read the result: Match.
The Formula
The Bicycle Bead Seat Diameter Checker formula is Fit = (Tire BSD = Rim BSD), with Bead Seat Circumference = π × BSD.
Fit = BSD_tire = BSD_rim Bead Seat Circumference = π × BSD Overall Diameter = (Rim Diameter × 25.4) + 2 × (Width × Aspect Ratio / 100)Worked example: a 622 mm BSD has a 1,954 mm (76.93 in) bead seat circumference. Measure the rim's bead seat circumference with a narrow tape and divide by π to find an unknown BSD.
Conversion Table
The Bicycle Bead Seat Diameter Checker conversion table lists 11 BSDs from 406 mm to 635 mm in mm and inches, with the bead seat circumference. The circumference column helps when measuring an unmarked rim with a tape.
Adjacent sizes are close: 584 mm and 590 mm differ by 6 mm, which is enough to stop a tire from seating.
| BSD (mm) | BSD (in) | Bead Seat Circumference (mm) | Bead Seat Circumference (in) |
|---|---|---|---|
| 406 | 15.984 | 1,275 | 50.22 |
| 451 | 17.756 | 1,417 | 55.78 |
| 507 | 19.961 | 1,593 | 62.71 |
| 559 | 22.008 | 1,756 | 69.14 |
| 571 | 22.480 | 1,794 | 70.62 |
| 584 | 22.992 | 1,835 | 72.23 |
| 590 | 23.228 | 1,854 | 72.97 |
| 597 | 23.504 | 1,876 | 73.84 |
| 622 | 24.488 | 1,954 | 76.93 |
| 630 | 24.803 | 1,979 | 77.92 |
| 635 | 25.000 | 1,995 | 78.54 |
What Is the Bicycle Bead-Seat Diameter Checker?
The Bicycle Bead Seat Diameter Checker is a tool that confirms a bicycle tire and rim share the same bead seat diameter. The BSD is the one bicycle tire dimension with zero tolerance.
A tire on a rim with a smaller BSD falls off; on a rim with a larger BSD it will not mount. The checker makes the comparison explicit.
Common Uses
The Bicycle Bead Seat Diameter Checker has 4 uses: purchase checks, unmarked rims, wheel builds and used bikes.
- Check purchases: Match tire and rim before ordering.
- Measure unmarked rims: Find BSD from a tape measurement.
- Build wheels: Confirm rim BSD for a tire choice.
- Inspect used bikes: Verify fitted tires match the rims.