Examples
Examples
Try the starting example
- Fixed chainstay centre distance (mm)
- 400
- Front tooth count
- 40
- Rear tooth count
- 20
- Chain pitch per rivet interval (mm)
- 12.7
- Extra rivet intervals from component-specific method
- 2
- Approximate geometric length plus entered allowance (rivet intervals)
- 95.313821
- Length rounded up to an even interval count
- 96
- Rounded length (mm)
- 1,219.2
- Additional length from even-count rounding (mm)
- 8.714477
Try another scenario
- Fixed chainstay centre distance (mm)
- 400
- Front tooth count
- 20
- Rear tooth count
- 20
- Chain pitch per rivet interval (mm)
- 12.7
- Extra rivet intervals from component-specific method
- 2
- Approximate geometric length plus entered allowance (rivet intervals)
- 84.992126
- Length rounded up to an even interval count
- 86
- Rounded length (mm)
- 1,092.2
- Additional length from even-count rounding (mm)
- 12.8
Calculation method
Calculation method
Approximate geometric length plus entered allowance (rivet intervals)
Let c=centre distance/pitch. Approximate an open two-sprocket loop as 2c+(front+rear)/2+(front−rear)²/(4π²c), then add the explicit extra interval count.
Length rounded up to an even interval count
Round upward to the next multiple of two rivet intervals.
Rounded length (mm)
Rounded interval count×pitch.
Additional length from even-count rounding (mm)
(Rounded count−unrounded count)×pitch.
Symbols and units
- a
- Fixed chainstay centre distance (mm)
- b
- Front tooth count
- c
- Rear tooth count
- d
- Chain pitch per rivet interval (mm)
- e
- Extra rivet intervals from component-specific method
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Assumptions & limits
Assumptions & limits
- A fixed-centre geometric approximation with an allowance you supply. It does not determine the correct allowance, chain type, derailleur capacity or suspension growth. Confirm physical sizing with the component-specific method before cutting; the linked source explains why sizing methods differ.
Are these inputs private?
These calculations run in your browser. A shared link contains the values you choose to share. Only questions submitted to the separate AI finder are sent to OpenAI.
Further reading
Park Tool: measured chain sizing, exceptions and checks ↗
Background reading; this does not imply endorsement or independent review of SumFizz.